Pliocene

Editor's note: The Pliocene is the period of the geologic timescale that spans the era from approximately 5.331 to 2.588 million years ago. It preceeds the Pleistocene and is subsequent to the Miocene Epoch.

This article on the Pliocene Epoch was written by P. D. P, Brian R. Speer, Samir Patel, Richard Chang, Adia Jackson, Pia Sorensen and Ying-Ying Wu.

Introduction

The picture below shows a modern herd of zebra grazing on an African savanna. Grazing mammals, such as members of the perissodactyl and artiodactyls diversified in the Miocene and Pliocene (5.3 to 1.8 million years ago) as grasslands and savanna spread across most continents.

(Source: UCMP)

The Pliocene was a time of global cooling after the warmer Miocene. The cooling and drying of the global environment may have contributed to the enormous spread of grasslands and savannas during this time. The change in vegetation undoubtedly was a major factor in the rise of long-legged grazers who came to live in these areas.
Additionally, the Panamanian land-bridge between North and South America appeared during the Pliocene, allowing migrations of plants and animals into new habitats. Of even greater impact was the accumulation of ice at the poles, which would lead to the extinction of most species living there, as well as the advance of glaciers and ice ages of the Late Pliocene and the following Pleistocene.

(Source: UCMP)

Subdivisions of the Pliocene

The chart at page left shows the major subdivisions of the Neogene, the last portion of the Tertiary Period, including the Pliocene. The Pliocene Epoch is part of the Cenozoic Era. 

Tectonics and paleoclimate of the Pliocene

The epoch was marked by a number if significant tectonic event that created the landscape of today. One such event was the joining of the tectonic plates of North and South America. This joining was brought about by a shift of the Caribbean plate, which moved slightly eastwards and formed a land bridge across the Isthmus of Panama. The connection between North and South America had a significant impact on flora and fauna in two respects. The first of these occurred on land: the creation of a land bridge enabled species to migrate between the two continents. This led to a migration of armadillo, ground sloth, oppossum, and porcupines from South to North America and an invasion of dogs, cats, bears and horses in the opposite direction. Second, the joining of the two tectonic plates also led to changes in the marine environment. An environment with species that had been interacting for billions of years now became separated into the Atlantic and Pacific oceans. This in turn had a significant impact on the evolution of the species which became isolated from each other.
During the Pliocene the tectonic plates of India and Asia also collided, which formed the Himalayan Mountains. In America, the Cascades, Rockies, Appalachians, and the Colorado plateaus were uplifted, and there was activity in the mountains of Alaska and in the Great Basin ranges of Nevada and Utah. The end of the Pliocene was marked in North America by the Cascadian revolution, during which the Sierra Nevada was elevated and tilted to the west. In Europe as well many mountain ranges built up, including the Alps, which were folded and thrusted.
Over the course of the Pliocene, the global climate became cooler and more arid. The beginning of the epoch saw numerous fluctuations in temperature, which gave way to the general cooling trend towards the end of the Pliocene. This long term cooling, in fact, started in the Eocene and continued up to the ice ages of the Pleistocene. During the Pliocene, large polar ice caps started to develop and Antarctica became the frozen continent that it is today.
It is uncertain what caused this cooling of the climate from the beginning to the end of the Pliocene period. Changes in the amount of heat transported by oceans has been suggested as one possible explanation; higher concentrations of greenhouse gases in the atmosphere may also have contributed. It is also possible that the raising of the Himalayan Mountains, caused by plate collisions between India and Asia, accelerated the cooling process.
Generally though, the climate of the Pliocene is thought to have been much warmer than it is today. The warmest phase was in the middle of the epoch, the interval between three and four million years ago. The climate was especially mild at high latitudes and certain species of both plants and animals existed several hundred kilometers north of where their nearest relatives presently exist. Less ice at the poles also resulted in a sea level regarded to have been about 30 meters higher than it is today.
Accompanying the general cooling trend of the Pliocene was, as already mentioned, an increased aridity. This led to a number of noteworthy changes in the environment. The Mediterranean Sea dried up completely and remained plains and grasslands for the next several million years. Another environmental change was the replacement of many forests by grasslands. This in turn favored grazing animals at expense of browsers. Generally these grazers also got larger and developed larger teeth suitable for a diet of grass. Also, the longer legs they developed enabled them to walk long distances to new feeding grounds and to detect and escape predators. It was also during this time that some apes came down from trees and started to exist on the plains in Africa. In fact, it is generally believed that Australopithecus evolved in the late Pliocene.

Climate Change Escape Routes

One if by Land, Two if by Sea?
Climate Change "Escape Routes"

Similar movement rates needed for animals and plants on land and in the oceans
One if by land, two if by sea? Results of a study published in the Science [Science Magazine, 4 November 2011] show how fast animal and plant populations would need to move to keep up with recent climate change effects in the ocean and on land. The answer: at similar rates.
The study was supported by the National Science Foundation (NSF), and performed in part through the National Center for Ecological Analysis and Synthesis.
"That average rates of environmental change in the oceans and on land are similar is not such a surprise," says Henry Gholz, program director in NSF's Division of Environmental Biology. "But averages deceive," Gholz says, "and this study shows that rates of change are at times greater in the oceans than on land--and as complex as the currents themselves."
Lobsters may need to keep up the pace to "out-run" the effects of
climate change. Credit: Hugh Brown, SAMS Greenhouse gases have warmed the land by approximately one degree Celsius since 1960. That rate is roughly three times faster than the rate of ocean warming. These temperatures have forced wild populations to adapt--or to be on the move, continually relocating. Although the oceans have experienced less warming overall, plants and animals need to move as quickly in the sea as they do on land to keep up with their preferred environments. Surprisingly, similar movement rates are needed to out-run climate change. On land, movement of 2.7 kilometers (1.6 miles) per year is needed and in the oceans, movement of 2.2 kilometers (1.3 miles) per year is needed.
"Not a lot of marine critters have been able to keep up with that," says paper co-author John Bruno, a marine ecologist at the University of North Carolina at Chapel Hill. "Being stuck in a warming environment can cause reductions in the growth, reproduction and survival of ecologically and economically important ocean life such as fish, corals and sea birds."
"With climate change we often assume that populations simply need to move poleward to escape warming, but our study shows that in the ocean, the escape routes are more complex," says ecologist Lauren Buckley of the University of North Carolina at Chapel Hill, also a co-author of the paper. "For example, due to increased upwelling, marine life off the California coast would have to move south [rather than north] to remain in its preferred environment."
"Some of the areas where organisms would need to relocate the fastest are important biodiversity hot spots, such as the coral triangle region in southeastern Asia," says lead author Mike Burrows of the Scottish Association of Marine Science.

Halocarbon

  A halocarbon is an organic chemical molecule composed of at least one carbon atom bound covalently with one or more halogen atoms; the most common halogens in these molecules are fluorine, chlorine, bromine and iodine. Naturally occurring halocarbons are created by certain volcanic eruptions, forest fires, fungal decay, certain marine organism metabolism and are found in tissues of diverse organisms ranging from marine snails to various plants.
Many halocarbons become air pollutants, water pollutants in surface and groundwater resources and as soil contaminants. In the atmosphere, some of these chemicals produce significant impacts of upper atmosphere ozone depletion and also as radiative forcing gases implicated in climate change. In fact, many scientists have suggested that effective regulation of halocarbons may be a more cost effective approach to mitigating global warming than extensive regulation of the much weaker greenhouse gas, carbon dioxide.

Natural occurrence

The most commonly occurring halocarbon is methyl chloride (CH3Cl), which is produced variously through fungal decay, marine organism metabolism and burning of biomass (e.g. forest fires). Due to spatial variations in these processes, the lower atmospheric concentration of methyl chloride varies from 500 to 2000 parts per trillion by volume (pptv); however, mean tropospheric wide levels are around an estimated 600 pptv.

Man-made sources

Slash-and-burn practice, Morondava, Madegascar. Source: Frank Vassen
Principal anthropogenic sources of halocarbons are: (a) release of refrigerants into the atmosphere; (b) accidental release of tetrachloroethylene, carbon tetrachloride and other industrial solvents into the environment; and (c) slash-and-burn agriculture, whereby indigenous people burn forests for quick yields of charcoal and first year crops.

Natural sinks

Halocarbons find their way into the atmosphere from both natural occurrence and through escape from manufactured products. However, there are natural sinks at work, whose potency is difficult to compute, due to the low concentrations of halocarbons, and due to the infinite variety of halocarbon compounds, microbial agents and environmental variables. Sinks include bacterial dehalogenation in air, water and soil media.
In the troposphere dehalogenation by the hydroxyl ion is an important sink, whereas stratospheric dehalogenation involves important contributions from excited oxygen and chlorine ions.
The reductive dehalogenation capability of certain microbes such as Methanosarcina barkerii has been known to act on numerous chlorinated halocarbons for some time. Soil sinks have been studied sufficiently to determine that they are robust removal agents. The upper two meters of aerobic soils have been extrapolated to be responsible for removal of about forty percent of all atmospheric carbon tetrachloride.
Since man-made halocarbons have been emitted in large quantities into the environment for many decades, and natural sources for hundreds of thousands of years, oceanic concentrations of many of these chemicals are in quasi-equilbrium, particularly in the Epipelagic zone, where mixing is robust. For example, concentrations of carbon tetrachloride is found to be approximately 0.25 of saturation at a depth of 95 meters in the sub-oxic zone of Saanich Inlet, British Columbia, while CFC-12 is at virtually saturation at the same depth.
To demonstrate the efficacy of bacterial dehalogenation, in the Gotland Basin of the Baltic Sea, carbon tetrachloride and CFC-11 are severely depleted in the shallow anoxic zone compared to surface concentrations, due to robust anoxic bacterial attack.
Methyl chloride and methyl bromide are also subject to natural process anaerobic bacterial dehalogenation. As a more specialized example, methyl chloride was found to undergo efficient dehalogenation within an anaerobic cyanobacterial mat on the shoreline of Mono Lake, where anoxic conditions were present within three millimeters of the mat surface.

History and uses

The first sythesis of a chlorocarbon was carried out by Michael Faraday in 1821, with creation of  tetrachloroethene. In the late 1890s Belgian chemist Frederic Swarts was the first to synthesize a fluorocarbon in the laboratory. Not until 1928 did halogens realize commercial importance, when DuPont chemist Thomas Midgely Jr. created a fully halogenated compound for use as a refrigerant. By the 1970s chloroflorocarbons were in broad industrial use as the main working fluid for refrigerant systems, air conditioning gases, as aerosol propellants, foam producing agents, solvents, dry cleaning chemicals, and paint strippers.

Environmental contamination and toxicity

Tetrachloroethylene tankage used in dry-cleaning
Source: Montana DEQ
Many halocarbons are fundamentally troublesome, due to the volatility of many of these compound to escape into the atmosphere, and due to relatively high solubility and persistence in groundwater and soil, when they are released into surface waters or rupture of underground storage tanks. As air pollutants, many of the halocarbons are both toxic and carcinogenic.
The most prevalent origin of major groundwater contamination is from rupture or spillage of tetrachloroethylene storage tanks, since these have been used broadly throughout the industrialized world for dry cleaning solvents. Prior to the 1980s the common standards, even in Western countries, did not require double-containment, so that there accumulated thousands of subsurface plumes of tetrachloroethylene, rendering groundwater supplies both carcinogenic as well as toxic; many of these plumes extend more than one kilometer from the point of release.

Greenhouse gases

Since most halocarbons absorb radiant reflected sunlight, they contribute to the heating of the troposphere, and thus function as a greenhouse gas. Residence times of a given halocarbon vary significantly. In particular, some are relatively unstable with tropospheric residence times on the order of hours or a few days; iodomethane, for example, is one of these reactive gas molecules. Initially most of the refrigerants used were freon and related chlorofluorocarbons; however, the long residence times of such compounds in the atmosphere led to replacement of preferred refrigerant gases to the more reactive hydrochlorofluorocarbons, whose atmospheric residence time is a lesser ten to fifteen years half-life.
Although there is a wide variation in the Global Warming Potential (GWP) among the halocarbons, these chemicals generally have a much greater GWP than either methane or carbon dioxide. For example, HFC-23 (CF3H) has an atmospheric halflife of 264 years and GWP of 9200; HFC-125 has an atmospheric halflife of 33 years and GWP of 4800; HFX-124a has an atmospheric halflife of 15 years and a GWP of 3300; HFC-152a (CF2HCH3) has an atmospheric halflife of two years and a GWP of 460 years; HFC-227ea has an atmospheric halflife of 37 years and a GWP of 4300; perfluoromethane has an atmospheric residence time of 50,000 years and a GWP of 4400; perfluoroethane has an atmospheric halflife of 10,000 years and a GWP of 6200.
In terms of time trends, some halocarbons such as carbon tetrachloride are in atmospheric decline, whereas other molecular species such as HFC-23 and HCFC-22 are steadily rising as of the early 21st century.

Ozone depletion

Halocarbons which reach the stratosphere have significant effects of destroying the ozone layer. The efficacy of ozone destruction is often measured by a comparative unit termed Ozone depletion potential (ODP), which is based upon the ODP of trichlorofluroomethane (CFC-11) being assigned a value of unity.
The international agreement known as the Montreal Protocol has been responsible for reduction of most chlorofluorocarbons, especially in Western countries.
Time lapse view of atmospheric ozone over North America, assuming absence of Montreal Protocol. Source: NASA Goddard        

Habitat fragmentation

Habitat fragmentation involves alteration of habitat resulting in spatial separation of habitat units from a previous state of greater continuity.

Figure 1. Aerial photograph of dry forest scrub in southern Zambia, fragmented by agricultural land conversion. 2008. Source: C.Michael Hogan

This phenomenon occurs naturally on a geologic time-scale or in unusual and catastrophic events: however, since the Holocene era, humans have produced dramatic and swift transformation of landscapes throughout the world, resulting in a level of habitat fragmentation that has induced worldwide reduction in biodiversity and interuption of  sustainable yields of natural resources.
Humans produce habitat fragmentation chiefly from agricultural land conversion, urbanization, pollution, deforestation and introduction of alien species; ironically, both human caused wildfires as well as the systematic practice of fire suppression can also create habitat fragmentation. Prior to the dominance of mankind, long term changes engendered by geologic processes or climate oscillations contributed to habitat fragmentation.

Geometric factors

Figure 2. The Great Wall of China has existed for two millennia as one of the largest man-made habitat fragmentation constructs. Source: C.Michael Hogan

Habitat fragmentation can manifest in an endless array of geometries, depending on the shape and extent of the separation zone.
It is important to note that the separation distance required for effecting fragmentation may vary considerably depending upon the dynamics of reproduction of key species involved. These factors include such spatially related parameters as distance typically traveled for faunal mating, seed dispersal radii, seasonal migration patterns and diurnal faunal foraging. In general, the smallest of these characteristic distances must be regarded as the controlling factor in order to respect the integrity of the ecosystem.

There is a sizeable suite of geometric measures that can be useful in describing the patch geometry of a fragmented habitat^[1]; some of these major factors are patch area, number of patches, ratio of patch size distribution and the patch edge length to area ratio. Fundamentally, the risk of extinction from habitat fragmentation generally increases with terrestrial animal size, since home range and migration needs are largest; however, small terrestrial fauna and plants with compact seed dispersal patterns are vulnerable to very small separations of habitat patches.

Natural processes of fragmentation

Figure 3. Colorado River viewed from Dead Horse Point, Utah. The canyon depth here is approximately 600 meters, where the river has gradually cut a wide separation of the original continuous habitat of the Colorado Plateau. Source: C. Michael Hogan

The chief natural phenomena that have driven fragmentation are glacial advances, volcanic activity, geologic faulting, tectonic movement, mass land slumping, serpentinization, major sea level rise and climate oscillation. Each of these actions has the potential to create irreversible effective isolation of previously connected habitat units; note that, for example, climate oscillations or minor glacial advances lasting only a few centuries have a reasonable probability that the landscape will revert, since mass extinctions are not necessarily produced from natural oscillatory functions having an effective time scale this small, especially since regional refugia can mitigate losses of such scale.
Major glacial advances may have taken tens or hundreds of thousands of years, such that the resulting habitat fragmentation is likely to have translated into new speciation as well as extinction of populations that were driven below minimum viable population size. One notable example of long timescale fragmentation on a large scale is the Andean uplift in the Amazon Basin. In this pre-Pleistocene epoch topographic change occurred so slowly that the uplift engendered further speciation and actually enhanced biodiversity.^[2]

Biodiversity implications

Habitat fragmentation is a significant cause of biodiversity destruction.^[3] Research has demonstrated that fragmentation characteristically reduces species richness and taxon diversity, and may reduce the efficacy of ecosystem functioning. Fragmentation not only reduces the amount of functional habitat, but it may isolate a species population into subpopulations, that may be sufficiently near the minimum viable population size to risk local extinction from successive demographic processes or catastrophic events. The mechanics of these impacts often relate to the alteration of relationships among species. In some cases the population of certain species may actually increase within the fragmented habitat complex; however, these few increases are typically already dominant or keystone species, and such increases are usually at the expense of reducing populations of (if not elimination of) other species.  With an original habitat becoming fragmented, some species have insufficient dispersal robustness to travel among the fragmented patches. In these cases such taxa may suffer from genetic drift or inbreeding due to restricted gene flow, and may have difficulty in re-colonizing^[4] or rescuing a subpopulation from local extirpation. Even if a given species has dispersal strength, it may suffer from insufficient dispersal and survival of taxa with which it interacts.
Considerable research has been conducted on species impacts to vertebrates, being macroscopically observable in the landscape, and on flora, since they are somewhat stationary whilst being analyzed. Notably there is a lack of data on arthropods, which comprise most of the extant biomass of our planet. Furthermore, the position of arthropods within an ecosystem place them in a role of considerable influence on the entirety of ecosystem services. Conservation biologists have developed  the concept of habitat corridors as partial mitigation for the adverse impacts of habitat fragmentation.
The adverse biodiversity impacts can be extended in time consequence. For, example Lovejoy and Hannah note that the massive pre-1850 New Zealand and Australian deforestation by aborigines and Europeans continues to express and magnify its adverse manifestation on the landscape.^[5] The same authors make the interesting conjecture that the presently extant species which have successfully survived the dramatic climate fluctuations of the Quaternary (with attendant large swings in species populations) may be somewhat immunized to future climate oscillations.

 Examples

One of the most widely studied examples of habitat fragmentation is in the Central Amazon Conservation Complex of Brazil, where a number of controlled studies were conducted in the 1980s. Due to pressures of an expanding human population and associated economic pressures, the Brazilian government embarked on a permissive policy of systematic and large scale forest destruction. In one study north of Manaus these residual patches were variously created in one, ten and 100 hectare sizes.^[6] Resident bird species, both frugivores and insectivores, were studied over a seven year period post-clearing. Results showed that bird densities declined in residual patches, with the smaller patches suffering the greatest species loss, even though initial response of small patches showed fewer initial losses as measured by bird density. An even larger long time scale loss of species richness was evident from the century long trend of deforestation in the area, since many of the plots cleared from 100 years ago were enjoying no economic use, but did not effectively rebound with complete forest cover; in a certain number of cases reasonable regrowth of secondary forest occurred. The conclusion drawn is that the ecological damage from long term deforestation and resulting habitat fragmentation has been disproportionately related to the actual economic taking of forest.
Two classical examples of habitat fragmentation from the continent of Asia. A-B. The Himalayas and C-D. The Sunderbans have been massively impacted due to habitat fragmentation both due to natural geological causes as well anthropogenic factors severely interfering into the life cycle of local flora and fauna. Source: Saikat Basu, own work
A small scale example of grassland fragmentation has yielded considerable evidence of biodiversity change. While dominant grass species were not severely altered, there were significant changes in arthropod and other faunal characteristics.^[7] The target location were calcareous grasslands in central Europe, that are high in species richness. This class of European grasslands often include considerable hectarage that have been partially cultivated by humans, are which are, in fact, effective refugia for grass and forb taxa that might otherwise have become extinct. Ongoing threats to further fragmentation are over-fertilisation and ironically reforestation and abandonment. That is to say, these human induced constructs contain many species that are now dependent on man's continued tending as these units co-evolved with the advent of agriculture in the early Holocene. Braschler found that butterfly species richness declined in the face of habitat fragmentation. While populations of certain dominant ant species (notably Lasius paralienus) as well as certain aphid taxa increased, these increases came at the expense of population losses of  numerous rarer taxa. The implications of abetting an already dominant arthropod taxon at the diminution of a plethora of other species suggests adverse impacts of habitat fragmentation upon biodiversity..
The Three Gorges Dam on China's Yangtze River represents the largest scale anthropomorphic intrusion into freshwater habitat in history. This aquatic barrier is a threat to the survival of numerous fish species and other aquatic biota. Besides the obvious impact to migratory species that utilize river reaches above and below the dam, there are extensive impacts to turbidity and hydrological characteristics that alter the natural habitat of hundreds of species.^[8] There were 162 endemic fish species recorded prior to dam development, 44 of which are endemic to the Yangtze Basin. Severing the upstream and downstream portions of the river by dam construction is expected to threaten the survival of 20 fish species, with six of them having a high probability of extinction. In addition to severing the aquatic habitat, the dam construction also severs the riparian zone on both sides of the river with dam anchorages and other industrial infrastructure, leading to fragmentation of that terrestrial habitat.

Terrestrial biome

Introduction

Many places on Earth share similar climatic conditions despite being found in geographically different areas. As a result of natural selection, comparable ecosystems have developed in these separated areas. Scientists call these major ecosystem types biomes. The geographical distribution (and productivity) of the various biomes is controlled primarily by the climatic variables precipitation and temperature. The maps in Figures 1 and 2 describe the geographical locations of the thirteen major terrestrial biomes of the world. Because of their scale, these maps ignore the many community variations that are present within each biome category.
Most of the classified biomes are identified by the dominant plants found in their communities. For example, the various types of grasslands are dominated by a variety of annual and perennial species of grass, while deserts are occupied by plant species that require very little water for survival or by plants that have specific adaptations to conserve or acquire water.
The diversity of animal life and subdominant plant forms characteristic of each biome is generally controlled by abiotic environmental conditions and the productivity of the dominant vegetation. In general, species diversity becomes higher with increases in net primary productivity, moisture availability, and temperature.
Adaptation and niche specialization are nicely demonstrated in the biome concept. Organisms that fill similar niches in geographically separated but similar ecosystems usually are different species that have undergone similar adaptation independently, in response to similar environmental pressures. The vegetation of California, Chile, South Africa, South Australia, Southern Italy and Greece display similar morphological and physiological characteristics because of convergent evolution. In these areas, the vegetation consists of drought-resistant, hard-leaved, low growing woody shrubs and trees like eucalyptus, olive, juniper, and mimosa.

Tundra

The geographical distribution of the tundra biome is roughly poleward of 65° North latitude. In the Southern Hemisphere, the tundra biome has a very limited distribution. Within the tundra biome, temperature, precipitation, and evaporation all tend to be at a minimum. In fact, the tundra is the coldest of all biomes and this environmental factor has played an important role in the evolution of adaptations for plant and animal survival. Most tundra locations, have summer months with an average temperature between 3 and 12° C (37 to 54° F). The average winter monthly temperature is around -34° C (-30° F). Precipitation in the wettest month is usually no greater than 2.5 centimeters (roughly 1 inch). Yet, despite the low levels of precipitation the ground surface of the tundra biome is often waterlogged because of low rates of evapotranspiration and poor drainage.
The tundra biome is characterized by the absence of trees and the presence of low-lying shrubs, mosses, and lichens. Lack of height allows the vegetation to be protected by the insolating properties of snow during the winter season. Perhaps the most characteristic arctic tundra plants are lichens like reindeer moss (Cladonia spp.). In the drier parts of the tundra, grasses are common (Figure 3). Sedges dominate sites that have more moisture. About 400 varieties of flowering plants occur in this biome. Total species diversity of plants in the tundra biome is relatively small numbering about 2000 species. Plants are generally small, are adapted to soil disturbance, and reproduce via budding or other forms of asexual reproduction rather than sexual means. Soils of this biome are usually permanently frozen (permafrost) starting at a depth of a few centimeters to meter or more. The permafrost line is a physical barrier to plant root growth. Thus, there are no deep rooting systems. The presence of permafrost also causes poor drainage and soils are often waterlogged and chemically reduced.
Figure 3: Tundra dominated by flowering arctic cotton grass, Northwest Territories, Canada. (Image Source).
The principal herbivores of the tundra biome include caribou, musk ox, arctic hare, voles, squirrels, and lemmings (Figure 4). Most of the bird species of the tundra have the ability to migrate and live in warmer locations during the cold winter months. The herbivore species support a small number of carnivore species like the arctic fox, snow owl, polar bear, and wolves. Reptiles and amphibians are few or completely absent because of the extremely cold temperatures.
Alpine tundra is quite comparable to arctic tundra but differs in the absence of permafrost, the presence of better drainage, and more extreme annual fluctuations of air temperature. Plants species in the alpine tundra are for the most part similar to the ones found on the arctic tundra. In contrast, alpine tundra animal species tend to be quit different from those individuals that live in the arctic tundra. This takes place because alpine tundra tends to adopt migrating species during the summer months from habitats located at lower elevations.

Boreal Forests/Taiga

This moist-cool, transcontinental boreal forests or taiga biome lies largely between 50 and 65° North latitude. The climate of this biome is cool to cold with more precipitation than the tundra. Precipitation here mainly occurs in the summer because this is the season when mid-latitude cyclones move in from the south. The growth season is limited to about 130 days.
The predominant vegetation of boreal forest biome is cone bearing needle-leaf evergreen variety tree species. Four tree genera are dominant in this biome: spruce (Picea), pine (Pinus), fir (Abies), and larch (Larix). In North America, some common species include: black spruce (Picea mariana), white spruce (Picea glauca), jack pine (Pinus banksiana), tamarack (Larix laricina), and balsam fir (Abies balsamea); with red pine (Pinus resinosa), white pine (Pinus strobus), and hemlock (Tsuga canadensis) limited to an area north and east of the Great Lakes Region. Broad-leaf species, like alder (Alnus), birch (Betula), and aspen (Populus), are common in all areas as an early successional species after disturbance.
Understory vegetation is relatively limited as a result of the low light penetration even during the spring and fall months. Common understory species include orchids, shrubs like rose, blueberry, and cranberry. Mammals common to the boreal forest include moose, bear, deer, wolverine, marten, lynx, wolf, snowshoe hare, vole, chipmunks, shrews, and bats. Reptiles are extremely rare, once again, because of cold temperatures. 
Deep litter layers are a common characteristic of boreal forest soils. These deep litter layers accumulate because of slow decomposition rates. Soils of this biome are also acidic and mineral deficient. Mineral deficiency occurs because large amounts of water move down though the profile causing leaching.
Boreal forest soils are characterized by a deep litter layer and slow decomposition. Soils of this biome are also acidic and mineral deficient because of the large movement of water vertically though the profile and subsequent leaching.

Temperate Coniferous Forests

In North America we can find two broad areas of temperate coniferous forests in the more temperate mid-latitudes. In these areas, average annual temperatures range from 20° to 5° C (68° to 41° F). Along the west side of North America and below the boreal forest is one such area. On the wetter sites (up to 400 centimeters or 160 inches annually) that have close proximity to the Pacific Ocean are stands of very tall and productive Douglas fir (Pseudotsuga menziesii), red cedar (Thuja plicata), sitka spruce (Picea sitchensis), and redwood (Sequoia sempervirens). Some of these trees can grow to over 120 meters (390 feet) in height. Beneath the canopy of these trees is a shrub layer that includes various types of berries (Vaccinium spp.), a few herbs, and various ferns. Further inland of this temperate “rain forest” zone precipitation declines significantly, winter temperatures become colder, and summer temperatures become much warmer. This change in climate makes more drought resistant trees like ponderosa pine (Pinus pondersoa), Engelmann spruce (Picea engelmannii), and lodgepole pine (Pinus contorta) dominant.
Another region of temperature coniferous forests occurs in southeastern United States. The species composition of this forest ecosystem does not resemble the coniferous forests found in western North America. Instead, these forests are dominated by pitch pine (Pinus rigida), longleaf pine (Pinus palustris), and slash pine (Pinus elliotti). All of these tree species are adapted to growing on nutrient poor sandy soils and can withstand the effects of fire. Biomass productivity is typically low in this type of temperate coniferous forest.
Outside of North America, the various types of temperate coniferous forest can also be found in northern Japan, and parts of Europe and Asia. In these areas, the plant species are similar in form and ecological function to North American species but not closely related.

Temperate Broadleaf and Mixed Forests

The temperature broadleaf and mixed forests biome (also called temperate deciduous forest) is characterized by a moderate temperate climate and a dominance of broadleaf deciduous trees. This biome once occupied much of the eastern half of the United States, central Europe, Korea, and China. Over the last few centuries, this biome has been very extensively affected by human activity. Much of it has been converted into agricultural fields or urban land-use.
Tree species diversity is this biome is moderate with 5 to 25 dominant trees at a site. Dominant trees include maple (Acer spp.), beech (Fagus spp.), oak (Quercus spp.), hickory (Carya spp.), basswood (Tilia spp.), magnolia (Magnolia spp.), cottonwood (Populus spp.), elm (Ulmus spp.), and willow (Salix spp.). The understory of shrubs, herbs, and ferns in a mature forest are typically well developed and richly diversified. Understory plants in this biome often take advantage of the leafless condition of trees during spring and fall to concentrate their growth.
Many different types of herbivores and carnivores live in the temperate broadleaf and mixed forest. Common fauna include squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and bears. Some reptiles and amphibians also exist here.
Nutrient rich brown forest soils characterize the temperate broadleaf and mixed forests biome. Tree cover promotes the accumulation of organic materials in a well-developed humus layer. Surface litter layer in these soils tends to be thin because of rapid decomposition.

Temperate Grasslands, Savannas and Shrublands

In central North America is the temperate grasslands, savannas and shrublands biome (also called prairie). The grassland biome is also found in the continental interior of Eurasia, Australia, and South America. Prior to the arrival of settlers in North America, much of this biome was dominated by species of tall grass known as bluestem (Andropogon spp.). This particular species covered much of the eastern side of this biome forming dense covers 1.5 to 2.0 meters (4 to 6 feet) tall. In the western end of the biome, where precipitation is lower, buffalo grass (Buchloe dactyloides) and other grasses only a few inches above the soil surface are common. Flowering herbs, including many kinds of composites and legumes, are common but much less important than grass species. Trees are found scattered in moist low-lying areas and along a narrow zone adjacent to streams.
Climatically, the temperate grasslands, savannas and shrublands biome can be described as being temperate. Summers are hot to warm and winters are cool to cold. Annual precipitation is less than what is received by the adjacent temperate broadleaf and mixed forests biome. Seasonally, precipitation varies from being concentrated during a few months to spread evenly through the year. This biome generally does not receive enough precipitation to support tree growth. In the wetter parts of this biome nutrient rich black chernozemic soils are common. In many parts of the world, these extremely fertile soils now support crop growth. In drier parts of prairies, soils can be influenced by salinization.
Grassland mammals are dominated by smaller burrowing herbivores (prairie dogs, jack rabbits, ground squirrels, and gophers) and larger running herbivores such as bison, pronghorn antelope, and elk. Carnivores include badger, coyote, ferret, wolf, and cougar. The populations of many of these organisms have been drastically reduced because of the conversion of their natural habitat into cropland. Some of these species are on the edge of extinction.

Montane Grasslands and Shrublands

The montane grasslands and shrublands biome is found at high elevations in temperate, subtropical, and tropical climates. This biome is dominated by grass and shrub species and tends to have a high number of endemic plants and animals. Examples of this biome can be found at the Tibetan plateau, Central Range in New Guinea, eastern Andes Mountains in South America, southeastern Africa, and tropical East Africa. A unique feature of many tropical examples of this biome is the presence of giant rosette vegetation belonging to the plant families Lobelia (Africa), Puya (South America), Cyathea (New Guinea), and Argyroxiphium (Hawaii) (Figure 7k-16). All of these plants have unique adaptations that allow them to successfully grow at high elevations.

Deserts and Xeric Shrublands

In its most typical form, the xeric shrublands and desert biome consists of shrub-covered land where the plants are spatially quite dispersed. This biome is geographically found from 25 - 35° North and South latitude, primarily in the interiors of continents. The formation of precipitation in desert and xeric shrublands biome is limited by the subtropical high-pressure system. Many desert areas have less than 3 centimeters (about 1 inch) of precipitation during an average year.
Dominant plants include drought resistant shrubs like the creosote bush (Larrea divaricata) and sagebrush (Artemisia tridentata), water storing succulents like cactus, and many species of short lived annuals that complete their life cycles during infrequent and short rainy periods (Figure 7k-18). Lastly, desert habitats can be completely devoid of vegetation if precipitation is in very short supply. Most desert mammals tend to be nocturnal to avoid the high temperatures. Desert habitats have a rich lizard and snake fauna because high temperatures promote the success of cold-blooded life forms. Because biomass productivity is low, the litter layer is almost nonexistent and organic content of surface soil layers is very low. Finally, evaporation tends to concentrate salts at the soil surface.

Mediterranean Forests, Woodlands and Scrub

The Mediterranean forests, woodlands and scrub biome (also called chaparral) has a very specific spatial distribution. It is found in a narrow zone between 32 and 40° latitude North and South on the west coasts of the continents. This area has a dry climate because of the dominance of the subtropical high pressure zone during the fall, summer, and spring months. Precipitation falls mainly in the winter months because of the seasonal movement of the polar front and associated mid-latitude cyclones. Precipitation varies from about 30 to 75 centimeters (12 to 30 inches) annually and most of this rain falls in a period only 2 to 4 months long.
Despite the fact that this biome is very limited geographically, it contains a high diversity of animal and plant species that are adapted to the stressful conditions of long, hot summers with little rain. The vegetation of this biome consists of many different types of annuals and drought-resistant, evergreen, short woody shrubs and trees. Dominant tree species include olive (Olea europaea), eucalyptus (Eucalyptus spp.), arbutus (Arbutus unedo), acacia (Acacia spp.), maritime pine (Pinus pinaster), and various species of oak (Quercus spp.). As a result of the climate, the vegetation of this biome exhibits a number of adaptations to withstand drought and fire. Plants tend not to drop their leaves during the dry season because of the expense of replacement. The dry climate slows the rate of leaf decomposition and soils tend to be poorly developed.

Tropical and Subtropical Grasslands, Savannas and Shrublands

Vegetation in the tropical and subtropical grasslands, savannas and shrublands biome (also called savanna) consists of a cover of perennial grass species 1 to 2 meters (3 to 6 feet) tall with scattered drought-resistant trees that generally do not exceed 10 meters (32 feet) in height. The savanna biome constitutes extensive areas in eastern Africa, South America, and Australia. Distinct wet and dry seasons and temperatures that are hot all year long characterize the climate of this biome. Annual rainfall varies between 90-150 centimeters (35 to 60 inches).
Tree and shrub species in the savanna usually drop their leaves during the dry season. This adaptation reduces water loss from the plants during the dry winter season. Diversity of plant and animal species tends to be high. Grazing on the grasses and trees are vast herds of hoofed mammals including buffalo, giraffes, eland, impalas, oryx, gazelles, gerenuk, wildebeest, zebra, rhinoceroses, elephants, and warthogs. These herbivores supply food for carnivores like lions, cheetahs, leopards, jackals, and hyenas.

Flooded Grasslands and Savannas

In the tropical and subtropical regions of our planet are large expanses of flooded grasslands and savannas. This biome is slightly different from the savanna biome just described. Because of common flooding, these areas support additional plant and animal species adapted to thrive under this condition. For instance, this biome is home to large numbers of migratory and resident water birds.
Some examples of flooded grasslands and savannas include in the Everglades in Florida, the Sahelian flooded savannas, and the Zambezian flooded savannas. Similar to other tropical biomes, this biome has high species diversity. For example, the Everglades are home to some 11,000 species of seed-bearing plants, 25 species of orchids, 300 bird species, and 150 species of fish.

Tropical and Subtropical Moist Broadleaf Forests

The tropical and subtropical moist broadleaf forests biome (also called moist tropical rain forest) occurs in a zone about 10° of latitude either side of the equator. Annual rainfall generally exceeds 250 centimeters (100 inches) and is evenly distributed throughout the year. Temperature and humidity are relatively high through the year. Flora is highly diverse: a typical hectare (2.5 acres) may contain as many as 300 different tree species as compared to 20 to 30 in the temperate zone. The various trees of the moist tropical rain forests are closely spaced together and form a thick continuous canopy some 25 to 35 meters (80 to 115 feet) tall. Every so often this canopy is interrupted by the presence of very tall emergent trees (up to 40 meters or 130 feet) that have wide buttressed bases for support. Epiphytic orchids and bromeliads, as well as vines (lianas), are very characteristic of the moist tropical rain forest biome. Some other common plant species include ferns and palms. Most plants are evergreen with large, dark green, leathery leaves.
The ground surface of the moist tropical rain forest tends to be dark with only about 1% of the light intensity found above the forest canopy. These light poor conditions cause the understory to be sparsely vegetated. The few plants that grow at ground level do so by being able to tolerate low light levels. The moist tropical rain forest is also home to a great variety of animals. Some scientists believe that 30 to 50% of all of the Earth's animal species may be found in this biome. Most of these organisms are insects.
Decomposition is rapid in the tropical rain forest because of high temperatures and abundant moisture. Because of the frequent and intense rains, tropical soils are subject to extreme chemical weathering and leaching. These environmental conditions make tropical soils acidic and nutrient poor.

Tropical and Subtropical Dry Broadleaf Forests

Tropical and subtropical dry forests (also called seasonal tropical forest or tropical dry forest) are found in southern Mexico, southeastern Africa, central India, Indochina, Madagascar, New Caledonia, eastern Bolivia, central Brazil, the Caribbean, and along the coasts of Peru and Ecuador.This biome exists as a zone that borders the tropical and subtropical moist broadleaf forests biome. Because of its geographical location, the tropical and subtropical dry forest experiences a dry season that lasts several months. This abiotic condition has a great effect on living things in this biome. Many of these species that live here have specific adaptations to help them survive the dry period. Consequently, deciduous trees like teak, mahogany, and mountain ebony dominate these forests. During the seasonal drought these trees loose their leaves to conserve water.The leafless condition also causes more sunlight to reach ground surface and this condition facilitates the growth of thick shrub layer. While less diverse than tropical rain forests, seasonal tropical forests still have a vast assortment of organisms.

Tropical and Subtropical Coniferous Forests

The tropical and subtropical coniferous forests biome is characterized by diverse species of conifer (needle-leaf) trees.This biome has a very limited distribution and is found mainly in Mexico, Central America, and on the islands of Cuba, Dominican Republic, and Haiti where low levels of precipitation and moderate temperature variability occurs. The needle-leaf form of these trees is an adaptation to drought. This biome shares some of the plant and animal species common to tropical and subtropical savanna, dry broadleaf forest, and moist broadleaf forest. Understory vegetation composed of shrubs and small trees is well developed and diverse. Finally, many species of migratory birds and butterflies spend their winter in this biome.

Virus

A virus is a microscopic organism that can replicate only inside the cells of a host organism. Most viruses are so tiny they are only observable with at least a conventional optical microscope. Viruses infect all types of organisms, including animals and plants, as well as bacteria and archaea. Approximately 5000 different viruses have been described in detail at the current time, although it is known that there are millions of distinct types.^[1]  Viruses are found in virtually every ecosystem on Earth, and these minute life forms are thought to be the most abundant type of biological entity.^[2]  The study of viruses is known as virology, a specialty within the field of  microbiology. 
The common concept of viruses focuses on their role as pathogen. Actually, there are vast numbers of viral entities that are beneficial to individual species as well as providing ecosystem services. For example, a class of viruses known as bacteriophages can kill a spectrum of harmful bacteria, providing protection to  humans as well as other biota.
Viruses are key in the carbon cycle; their role in ocean biochemistry includes microbological metabolic—including decomposition—processes. It is this decomposition that stimulates massive carbon dioxide respiration of marine flora. That respiration annililates effectively about three gigatons of carbon each year from the atmosphere. Significantly, viruses are being developed as tools for constructive modern medicine as well as the critical field of nanotechnology.
Unlike prions and viroids, viruses consist of two or three parts: a helical molecule, protein coat and sometimes a viral wrapper. All viruses have genes constructed from either Deoxyribonucleic acid (DNA) or Ribonucleic acid (RNA)—long helical molecules that carry genetic information. All viruses have a protein coat that protects these genes, and some are wrapped in a viral envelope of fat that surrounds them when they are outside a cell. (Viroids do not have a protein coat and prions contain neither RNA nor DNA).
Viruses vary from simple helical and icosahedral shapes to more complex structures. Most viruses are approximately one hundred times smaller than an average bacterium. The origins of viruses in the evolutionary history of life are unclear. Some may have evolved from plasmids—fragments of DNA that can migrate between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.

Lifeform or not?

Viruses have no ability to metabolize on their own, but depend upon a host organism for replication and manufacture of chemicals needed for such replication. Rybicki has characterized viruses as a form "at the edge of life".^[3]  Viruses are found in  Modern taxonomy and that taxonomy considers viruses as a totally separate form of life from cellular organisms—and some would say that they are merely complex molecules with a protein coating and not a lifeform at all. Since viruses are capable of self replication, they are clearly some type of lifeform, and likely involved with the early evolutionary development of such other simple lifeforms as bacteria and protists.
Viruses differ, however, from the simpler autonomous replication of chemical crystals. This is since a virus can inherit a genetic mutation and is also subject to similar natural selection processes of cellular organisms. A virus cannot be labelled simply, therefore, as inanimate or lifeless. Here, we consider it a lifeform, but we adhere to current taxonomy and do not credit it with a parallel domain to other recognized cellular lifeforms.  

Evolution

Although there is no detailed catalogue of the evolutionary relationships of viruses and hosts, certain gerneral characterisations can be made. In some such viral groups as poxviruses, papillomaviruses and tobamoviruses, molecular taxonomy aligns generally with the genetic relationships of their hosts.^[4] This suggests that the affilations of those viral groups predate their present derivatives, and, in fact, that these three viral groups and their hosts likely co-evolved. There are clear examples where an otherwise genetically close group like the tobamoviruses include a genetiically outlying host; in particular, the tobamoviruses generally utilize plants of the Solanaceae family, but an orchid and a cactus virus can also be found in the group.
Recombination of genome parts of viruses poses a more vexing puzzle, since the events are virtually random pieces of an evolutionary chain. Retroviruses and luteoviruses are examples of viral groups where large numbers of recombinations have occurred to produce new organisms. Sometimes these produced genome splices occur naturally using fragments that are either viral or cellular in nature. In some cases the product is more of a re-arrangement of genomic parts—referred to as psuedo-recombination. The Western Equine Encephalovirus is a known example of this last category.
It is likely that viruses began host relationships with archaea and bacteria about two billion years ago; it has been suggested, however, that the proliferation of terrestrial vascular plants was the watershed event in evolution that enabled the explosion of numbers of viral organisms and pathways.^[5]

Taxonomy

Tobacco Mosaic Virus schematic diagram. Source: Univ. Wisconsin There are two complementary systems for viral taxonomy: the ICTV and Baltimore approaches. In the case of the ICTV taxonomy, there are five distinct orders: Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, and Picornavirales. Within that hierarchy reside 82 families, 307 genera, 2083 species.^[6]
David Baltimore devised an earlier system based on the method of viral messenger RNA synthesis.^[7] The Baltimore scheme is founded on the mechanism of  messenger RNA production.  Although viruses must replicate mRNAs from their genomes to produce proteins and reproduce, distinctly different mechanisms are employed within each viral family. Viral genomes may be single ((ss) or double-stranded (ds), may be RNA or DNA based, and may optionally employ reverse transcriptase (RT); furthermore single strand RNA virus helices may be either sense (+) or antisense (−). These nuances divide viruses into seven Baltimore groups.
This Baltimore classification of scheme is centered around the concept of messenger RNA replication, since viruses  generate messenger RNA from their genomic coding to produce proteins and thence replicate themselves. The resulting Baltimore groups are:

• I: dsDNA type (examples: Adenovirus, Herpesvirus, Poxvirus)
• II: ssDNA type (+)sense DNA (example: Parvovirus)
• III: dsRNA type (example: Reovirus)
• IV: (+)ssRNA type (+)sense RNA (examples: Picornavirus, Togavirus)
• V: (−)ssRNA type (−)sense RNA (examples: Orthomyxovirus, Rhabdovirus)
• VI: ssRNA-RT type (+)sense RNA with DNA intermediate to life-cycle (example: Retrovirus)
• VII: dsDNA-RT type (example: Hepadnavirus) 

Arctic marine environments

This is Section 10.2.1 of the Arctic Climate Impact Assessment
Lead Author: Michael B. Usher; Contributing Authors:Terry V. Callaghan, Grant Gilchrist, Bill Heal, Glenn P. Juday, Harald Loeng, Magdalena A. K. Muir, Pål Prestrud
The arctic marine environment covers about 13 million km², of which about 45% is a permanent ice cap that covers part of the Arctic Ocean. Seasonal sea ice forms during winter, and recedes during the short arctic summer, exposing large areas of open water. The marine environment is thus dominated by sea ice and by the dynamics of that ice and especially the location of the ice edge. The transition zone between the sea ice and the open water has intense algal growth in spring and summer, and it is the primary production by these phytoplankton that supports the arctic marine food webs. Only in exceptional cases can the energy that drives the marine food webs be obtained from other sources. Discoveries of “hot vents” and “cold seeps” in the Arctic have been recently recorded. At these sites, bacteria are capable of deriving energy from methane (CH₄) or hydrogen sulfide (H₂S) gases that emerge as bubbles or in solution from the vents and seeps. These bacteria are then fed on by other organisms and so form the basis of some very specialized and localized food webs. Research on marine biodiversity is usually expensive, which is probably why comparatively less is known about marine biodiversity than terrestrial biodiversity.
Projected changes in sea ice, temperature, freshwater, and wind will affect nutrient supply rates through their effects on vertical mixing and upwelling. These will in turn result in changes in the timing, location, and species composition of phytoplankton blooms and, subsequently, in the zooplankton community and the productivity of fishes. Changes in the timing of primary production can affect its input to the pelagic community as well as the amount exported to and taken up by the benthic community. The retention: export ratio also depends on the advection of plankton and nutrients within the water body and on the temperature preferences of the grazing zooplankton; these both determine the degree of match or mismatch between primary and secondary production.
The projected disappearance of seasonal sea ice from the Barents and Bering Seas, and so the elimination of ice-edge blooms, would result in these areas having blooms resembling those presently occurring in more southerly seas. The timing of such blooms will be determined by the onset of seasonal stratification, again with consequences for a match or mismatch between phytoplankton and zooplankton production. If a mismatch occurs, due to early phytoplankton blooms, the food webs will be highly inefficient in terms of food supply to fish. Both export production and protozoan biomass is likely to increase. However, both the areal extent of export production and grazing by copepods are projected to increase slightly because of the larger ice-free area.
Future fluctuations in zoobenthic communities will be related to the temperature tolerance of the animals and to the future temperature of the seawater. Whereas most boreal species have planktonic larvae that need a fairly long period to develop to maturity, arctic species do not. Consequently, boreal species should be quick to spread with warm currents during periods of warming, while the more stenothermal arctic species (i.e., those only able to tolerate a small temperature range) will quickly perish. Shifts in the distribution of the fauna are likely to be quicker and more noticeable during periods of warming than periods of cooling. Change in the abundance or biomass of benthic communities is most likely to result primarily from the impact of temperature on the life cycles and growth rates of the species concerned. If warming occurs, thermophilic species (i.e., those tolerating a wide temperature range) will become more frequent. This will force changes to the zoobenthic community structure and, to a lesser extent, to its functional characteristics, especially in coastal areas.
Climate change affects fish production through direct and indirect pathways. Direct effects include the effects of temperature on metabolism, growth, and distribution. Food web effects could also occur, through changes in lower trophic level production or in the abundance of top-level predators, but the effects of these changes on fish are difficult to predict. However, generalist predators are likely to be more adaptable to changed conditions than specialist predators. Fish recruitment patterns are strongly influenced by oceanographic processes such as local wind patterns, mixing, and prey availability during early life stages; these are also difficult to predict. Recruitment success could be affected by changes in the timing of spawning, fecundity rates, larval survival rates, and food availability.
Poleward extensions of the range of many fish species are very likely under the projected climate change scenarios. Some of the more abundant species that are likely to move northward under the projected warming include Atlantic and Pacific herring (Clupea harengus and C. pallasi respectively), Atlantic and Pacific cod (Gadus morhua and G. macrocephalus respectively), walleye pollock (Theragra chalcogramma) in the Bering Sea, and some of the flatfishes that might presently be limited by bottom temperatures in the northern areas of the marginal arctic seas. The southern limit of colder-water fish species, such as polar cod (Boreogadus saida) and capelin (Mallotus villosus), are likely to move northward. Greenland halibut (Reinhardtius hippoglossoides) might possibly shift its southern boundary northward or restrict its distribution more to continental slope regions. Migration patterns are very likely to shift, causing changes in arrival times along the migration route. Qualitative predictions of the consequences of climate change on fish resources require good regional atmospheric and ocean models of the response of the ocean to climate change. There is considerable uncertainty about the effects of non-native species moving into a region in terms of their effects on the “balance” within an ecosystem.
The impacts of the projected climate change scenarios on marine mammals and seabirds in the Arctic are likely to be profound, but are difficult to predict in precise terms. Patterns of change are non-uniform and highly complex. The worst-case scenarios for reductions in sea-ice extent, duration, thickness, and concentration by 2080 threaten the existence of entire populations of marine mammals and, depending on their ability to adapt, could result in the extinction of some species.

Polar bears, ''Ursus maritimus''. (Photo credit: WWF-Norway 2002)

Climate change also poses risks to marine mammals and seabirds in the Arctic beyond the loss of habitat and forage bases. These include increased risk of disease for arctic-adapted vertebrates owing to improved growing conditions for the disease vectors and to contact with non-native species moving into the Arctic; increased pollution loads resulting from an increase in precipitation bringing more river borne pollution northward; increased competition from the northward expansion of temperate species; and impacts via increased human traffic and development in previously inaccessible, icecovered areas. Complexity arising from alterations to the density, distribution, or abundance of keystone species at various trophic levels, such as polar bears (Ursus maritimus) and polar cod, could have significant and rapid consequences for the structure of the ecosystems in which they currently occur.
Although many climate change scenarios focus on the potentially negative consequences for ecosystems, environmental change can also bring opportunities. The ability of some species to adapt to new climate regimes is often considerable, and should not be underestimated. Many marine vertebrates in the Arctic, especially mammals and birds, are adapted to dealing with patchy food resources and to a high degree of variability in its abundance.
Ice-living seals are particularly vulnerable to changes in the extent and character of the sea ice because they use it as a pupping, molting, and resting platform, and some species also forage on ice-associated prey. Of the arctic pinnipeds, ringed seals (Phoca hispida) are likely to be the most affected because so many aspects of their life history and distribution are tied to sea ice. They require sufficient snow cover to construct lairs and the ice must be sufficiently stable in spring for them to rear young successfully. Early breakup of the sea ice could result in premature separation of mother–pup pairs and hence increased neonatal mortality. Ringed seals do not normally haul out on land and to do this would be a very dramatic change in their behavior. Land breeding would expose ringed seal pups to much higher predation rates.
Changes in the extent and type of sea ice affect the distribution and foraging success of polar bears. The earliest impacts of warming will occur at their southern limits of distribution, such as at James and Hudson Bays. Late sea-ice formation and early break-up also mean a longer period of annual fasting. Reproductive success in polar bears is closely linked to their fat stores. Females in poor condition have smaller litters, as well as smaller cubs that are less likely to survive. There are also concerns that direct mortality rates might increase. For example, increased frequency or intensity of spring rains could cause dens to collapse, resulting in the death of the female as well as the cubs. Earlier spring break-up of sea ice could separate traditional den sites from spring feeding areas, and if young cubs were forced to swim long distances between breeding areas and feeding areas this could decrease their survival rate. The survival of polar bears as a species is difficult to envisage under conditions of zero summer sea-ice cover. Their only option would be to adopt a terrestrial summer lifestyle similar to brown bears (Ursus major), from which they evolved. But competition, risk of hybridization with brown and grizzly bears (both U. major), and an increase in human interactions, would also pose a threat to their long-term survival.
The effects of climate change on seabird populations, both direct and indirect, are very likely to be detected first near the limits of the species range and the margins of their oceanographic range. The southern limits of many arctic seabirds are likely to retract northward, also causing breeding ranges to shift northward. Changes in patterns of distribution, breeding phenology, and periods of residency in the Arctic are likely to be some of the first observed responses to climate change. Seabirds will also be affected by changes in prey availability and so can serve as indicators of ecosystem productivity. Since warmer (or colder) water would affect the distribution of prey species, the distribution of individual seabird species is likely to reflect changes in the distribution of macrozooplankton and fish populations. Changes in sea level may restrict the use of current breeding sites, but may increase the suitability of other sites that are not currently used owing to predator access or for other reasons.
With climate change already underway, planning for the conservation of marine biodiversity is an imperative. Series of actions are being proposed. These can be grouped into five key issues, namely:

• the implementation of an inventory of the Arctic’s biodiversity and of schemes for monitoring trends in the biodiversity resource, including appropriate indicators;
• the completion of a circumpolar network of marine and maritime protected areas;
• the development of circumpolar guidelines for managing arctic biodiversity in a sensitive manner, bearing in mind the needs of local communities and the fact that “controlled neglect” may be an appropriate means of management;
• the establishment of fora for developing integrated management schemes for coasts and seas; and
• the review of marine regulatory instruments, with recommendations for further actions where necessary.

Conservation is unlikely to be easy, but as many as possible of these five key issues should be developed on a circumpolar basis. This is particularly the case for the marine environment because many of the species tend not to be localized, but to be widely distributed throughout the Arctic Ocean as a whole. Indeed, some species have regular, seasonal patterns of migration. Satellite tracking has shown that walrus (Odobenus rosmarus) and narwhal (Monodon monoceros) can move great distances within the Arctic Ocean in relatively short periods of time. Similarly, polar bears, ringed seals, and beluga whales (Delphinapterus leucas) have been shown to exhibit extensive and rapid circumpolar movements.
The main requirement for the conservation of marine biodiversity is the need to take a holistic approach. The majority of national parks and reserves are predicated primarily upon the protection of coastal birds and mammals. This needs to be expanded to include the ecosystems upon which these birds and mammals depend, and upon which the commercially exploited fish populations also depend. It is not just the vertebrate animals that are important, but the whole range of biodiversity, and especially those small and often unknown organisms that are either trapping solar energy by photosynthesis or decomposing organic matter to enable the recycling of nutrients. It is the totality of the biodiversity of the marine habitats and ecosystems of the Arctic that support the sustainable production of the biological resources upon which the indigenous peoples, and others, depend.
Although there are many unknowns, it is likely that many of the vertebrate animals will move northward, with many of these species likely to become less abundant. However, for the phytoplankton, it is the extent of the mixing of the ocean layers that will determine the increases and decreases for the various taxonomic groups.