Crises caused by abiotic factors

Climate change is starting to have major impacts on ecosystems. With global temperature rising, there is a decrease in snow-fall, and sea levels are rising. Ecosystems will change or evolve to cope with the increase in temperature. Consequently, many species are being driven out of their habitats.

Polar bears are being threatened. They need ice for hunting seals, their primary prey. However, the ice caps are melting, making their hunting periods shorter each year. As a result, the polar bears are not developing enough fat for the winter; therefore, they are not able to reproduce at a healthy rate.

Fresh water and wetland ecosystems are dealing with extreme effects of the increase of temperature. The climate change could be devastating to salmon and trout and to other aquatic life. The increase in temperature will disrupt the current life patterns of the salmon and trout. The cold-water fish will eventually leave their natural geographical range to live in cooler waters by migrating to higher elevations.

While many species have been able to adapt to the new conditions by moving their range further towards the poles, other species are not as fortunate. The option to move is not available for polar bears and for some aquatic life.

Climate change

This section is an excerpt from Effects of climate change on ecosystems.[edit]

Rainforest ecosystems are rich in biodiversity. This is the Gambia River in Senegal's Niokolo-Koba National Park.

Climate change has adversely affected terrestrial^[1] and marine^[2] ecosystems, including tundras,^[3] mangroves, coral reefs, and caves.^[4] Increasing global temperature, more frequent occurrence of extreme weather,^[5] and rising sea level^[6] are examples of the most impactful effects of climate change. Possible consequences of these effects include species decline and extinction and overall significant loss of biodiversity, change within ecosystems, increased prevalence of invasive species,^[7] loss of habitats, forests converting from carbon sinks to carbon sources, ocean acidification, disruption of the water cycle, increased occurrence and severity of natural disasters like wildfires and flooding, and lasting effects on species adaptation.

Biodiversity extinction

This section is an excerpt from Biodiversity loss.[edit]

Summary of major biodiversity-related environmental-change categories expressed as a percentage of human-driven change (in red) relative to baseline (blue). Red indicates the percentage of the category that is damaged, lost, or otherwise affected, whereas blue indicates the percentage that is intact, remaining, or otherwise unaffected.^[8]

Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, depending on whether the environmental degradation that leads to the loss is reversible through ecological restoration/ecological resilience or effectively permanent (e.g. through land loss). The current global extinction (frequently called the sixth mass extinction or Anthropocene extinction), has resulted in a biodiversity crisis being driven by human activities which push beyond the planetary boundaries and so far has proven irreversible.^[8][9][10]

The main direct threats to conservation (and thus causes for biodiversity loss) fall in eleven categories: Residential and commercial development; farming activities; energy production and mining; transportation and service corridors; biological resource usages; human intrusions and activities that alter, destroy, disturb habitats and species from exhibiting natural behaviors; natural system modification; invasive and problematic species, pathogens and genes; pollution; catastrophic geological events, climate change, and so on.^[11]

Numerous scientists and the IPBES Global Assessment Report on Biodiversity and Ecosystem Services assert that human population growth and overconsumption are the primary factors in this decline.^{[12][13][14][15][16]} However other scientists have criticized this, saying that loss of habitat is caused mainly by "the growth of commodities for export" and that population has very little to do with overall consumption, due to country wealth disparities.^[17]

Climate change is another threat to global biodiversity.^[18][19] For example, coral reefs – which are biodiversity hotspots – will be lost within the century if global warming continues at the current rate.^[20][21] However, habitat destruction e.g. for the expansion of agriculture, is currently the more significant driver of contemporary biodiversity loss, not climate change.^[22][23]

International environmental organizations have been campaigning to prevent biodiversity loss for decades, public health officials have integrated it into the One Health approach to public health practice, and increasingly preservation of biodiversity is part of international policy, as part of the response to the Triple planetary crisis. For example, the UN Convention on Biological Diversity is focused on preventing biodiversity loss and proactive conservation of wild areas. The international commitment and goals for this work is currently embodied by Sustainable Development Goal 15 "Life on Land" and Sustainable Development Goal 14 "Life Below Water". However, the United Nations Environment Programme report on "Making Peace with Nature" released in 2020 found that most of these efforts had failed to meet their international goals.^[24] Of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only 6 were "partially achieved" by the deadline of 2020.^[25][26]

Animal overpopulation

In the wilderness, the problem of animal overpopulation is solved by predators. Predators tend to look for signs of weakness in their prey, and therefore usually first eat the old or sick animals. This has the side effects of ensuring a strong stock among the survivors and controlling the population.

In the absence of predators, animal species are bound by the resources they can find in their environment, but this does not necessarily control overpopulation. In fact, an abundant supply of resources can produce a population boom that ends up with more individuals than the environment can support. In this case, starvation, thirst, and sometimes violent competition for scarce resources may effect a sharp reduction in population, and in a very short lapse, a population crash. Lemmings, as well as other less popular species of rodents, are known to have such cycles of rapid population growth and subsequent decrease.

In an ideal setting, when animal populations grow, so do the number of predators that feed on that particular animal. Animals that have birth defects or weak genes (such as the runt of the litter) also die off, unable to compete over food with stronger, healthier animals.

In reality, an animal that is not native to an environment may have advantages over the native ones, such being unsuitable for the local predators. If left uncontrolled, such an animal can quickly overpopulate and ultimately destroy its environment.

Examples of animal overpopulation caused by introduction of a foreign species abound.

• In the Argentine Patagonia, for example, European species such as the trout and the deer were introduced into the local streams and forests, respectively, and quickly became a plague, competing with and sometimes driving away the local species of fish and ruminants.
• In Australia, when rabbits were introduced (unwillingly) by European immigrants, they bred out of control and ate the plants that other native animals needed to survive. Farmers hunted the rabbits to reduce their population and prevent the damage the rabbits did to the crops. They also brought cats to guard against rabbits and rats. These cats created another problem, since they became predators of local species.