Biodiversity, Conservation and Applied Ecology

Anthropogenic global warming

Anthropogenic global warming refers to the rise in mean global surface temperature caused mainly by human activities that add greenhouse gases to the atmosphere. Since the pre-industrial period, global mean temperature has risen by roughly 1 to 1.5 °C, and the IPCC attributes most of this rise to human emissions. The warming is the basis of the 1.5 °C and 2 °C limits in the Paris Agreement.

A greenhouse gas is a gas that absorbs outgoing infrared radiation from the Earth's surface and re-emits it, which warms the lower atmosphere. The principal anthropogenic greenhouse gases are carbon dioxide, methane and nitrous oxide, while water vapour is the most abundant natural greenhouse gas. Sulphur dioxide is not a greenhouse gas; its sulphate aerosols reflect sunlight and produce a net cooling effect.

The main processes that raise atmospheric greenhouse gases are the burning of fossil fuels, which releases carbon dioxide stored underground for millions of years, and land-use change such as tropical deforestation, which releases stored carbon and removes a carbon sink. Methane increases through enteric fermentation in ruminant livestock and through anaerobic decomposition in wetland soils. Molecular nitrogen does not absorb infrared radiation and is therefore not a greenhouse gas, even if its concentration changes.

The sharp rise in atmospheric CO_2 after 1950 is best explained by fossil fuel combustion, because industrial energy use grew rapidly after that date. Volcanic eruptions emit CO_2, but their long-term output is far smaller than anthropogenic emissions. Reducing greenhouse gas or methane emissions lowers warming, so such processes cannot be causes of the observed temperature increase.

Climate change impacts on species ranges

Species ranges respond to warming by moving toward cooler conditions. In mountains, this means an upslope shift in which both the lower and upper elevational limits rise. Points lying above the 1:1 identity line in a plot of elevational range midpoints or limits indicate an upward shift between two sampling dates.

If the lower elevational limit of a species keeps rising, its range is compressed against the mountain summit. A species whose lower limit approaches the summit has very little habitat left and is at high risk of local extinction, whereas species with low lower limits keep habitat for longer. This is why high-elevation specialists are often the first to decline on mountains.

The general pattern of warming-driven shifts is poleward in latitude, upslope in elevation, and deeper into cooler water in the ocean. Birds, mammals and fish all show these shifts. A movement toward the equator would take a species into warmer climates, so it is opposite to the expected response to warming.

C3 and C4 photosynthetic pathways respond differently to the environment. Rising CO_2 with no change in temperature favours C3 plants, because Rubisco in C3 plants is CO_2-limited and suffers more photorespiration. Rising mean annual temperature with CO_2 unchanged favours C4 plants, which concentrate CO_2 around Rubisco and are less affected by photorespiration at high temperature.

Conservation management actions

A conservation action benefits native species when it improves habitat quality, connectivity, resource supply or survival of native organisms. Planting native species in gardens and urban green spaces supplies nectar and shelter for native pollinators. Canopy bridges and similar crossings restore connectivity between forest patches, which allows arboreal animals to move and reproduce.

Some actions that appear helpful do the opposite. Planting an invasive alien species such as Prosopis juliflora displaces native vegetation and alters soil and water conditions, so it harms native species. Artificial lighting on nesting beaches attracts emerging hatchlings inland, which increases mortality of sea turtles.

Captive breeding is used for critically endangered species whose wild populations are too small to recover on their own. In India, the Great Indian Bustard is the focus of such breeding and head-starting programmes. Other threatened birds may be important conservation concerns without being the subject of this kind of intervention.

Reintroduction restores a species to part of its former range from which it has been lost. In India, Project Cheetah reintroduced African cheetahs after the Asiatic cheetah became extinct in the country. Animals such as the jaguar, which are native only to another continent, cannot be reintroduced into India.

Protection of foraging areas can allow a recovering population to grow in a logistic pattern. The growth equation is dN/dt = rN(1 - N/K), where the per capita growth rate (1/N)(dN/dt) = r(1 - N/K) falls as N approaches the carrying capacity K. The population growth rate is maximal at N = K/2, where the curve is steepest.

Endemism and biodiversity hotspots

An endemic species is one whose natural range is confined to a single geographic area, such as a country, a mountain range or an island. Endemism is highest in regions where topographic or climatic barriers isolate populations for long periods, so that many species occur nowhere else. Groups with restricted ranges, such as frogs of the Western Ghats, usually show more endemism than groups with wide distributions.

Several Indian mammals are native to the subcontinent but not endemic to India, because their natural ranges extend into neighbouring countries. The Bengal tiger and one-horned rhinoceros occur also in Nepal and other countries, and the cheetah is native to Africa and Iran. The lion-tailed macaque, which is restricted to the Western Ghats, is a true endemic of India.

Mammal distributions in India are linked to regional habitats. The Malabar giant squirrel is endemic to the Western Ghats, the pika lives in the cold high-altitude Western Himalaya, and the golden langur is native to the forests of Northeast India. The nilgai is an antelope of the plains of north and central India and is not native to these regions.

Zoonotic disease examples

A zoonotic disease is one transmitted from non-human animals to humans, either directly or through a vector or an intermediate host. Ebola virus disease arises from spillover from wildlife reservoirs such as bats and primates. Lyme disease is spread by ticks that acquire the bacterium from rodent and deer hosts.

HIV-AIDS originated from simian immunodeficiency virus in chimpanzees, and it is a classic example of zoonotic spillover. Nipah virus passes from fruit bats to humans, directly or through intermediate animals such as pigs. Kyasanur Forest Disease circulates among monkeys and ticks and infects humans through tick bites.

Diseases that are maintained only in human populations are not zoonotic. Poliomyelitis is caused by poliovirus, which has no animal reservoir. Cholera spreads mainly between humans through contaminated water and food, so it is not classed as zoonotic.