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Some impacts from increasing temperatures are already happening.

Ice is melting worldwide, especially at the Earth’s poles (mountain glaciers, ice sheets covering West Antarctica and Greenland, and Arctic sea ice).

Sea level rise became faster over the last century.

Precipitation (rain and snowfall) has increased across the globe.

Scientists tracked the decline of the Adélie penguins on Antarctica: from 32,000 pairs to 11,000 in 30 years.

Spruce bark beetles have boomed in Alaska due to 20 years of warm summers. The insects have chewed up 4 mln acres of spruce trees.

27. Biodiversity is genetic and phenotypic variation both within and among species, plus the variety of ecosystems created by these species.

Biodiversity is a term that can be used to describe biological diversity at a variety of different scales. In this context we will focus on the description of species diversity. Species play essential roles in ecosystems, so local and global species losses could threaten the stability of the ecosystem services on which humans depend. For example, plant species harness the energy of the sun to fix carbon through photosynthesis, and this essential biological process provides the base of the food chain for animal consumers. At the ecosystem level, the total growth of all plant species is termed primary production, and communities composed of different numbers and combinations of plant species can have very different rates of primary production. This fundamental metric of ecosystem function has relevance for global food supply and for rates of climate change because primary production reflects the rate at which carbon dioxide (a greenhouse gas) is removed from the atmosphere. There is currently great concern about the stability of both natural and human-managed ecosystems, particularly given the myriad global changes already occurring.

Biodiversityis the range and variety of organisms present in a given ecological community or

environment. Ecosystem diversity enhances ecosystem stability. Stability of ecosystems is very important as it is a part of stability of the biosphere.

 

Biodiversity is now known to affect ecosystem productivity, however, its effects on stability has been debated. To test the diversity–stability hypothesis a decade of data collection on the number of perennial prairie species, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity showed that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity. Thus, the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity.

28.


Date: 2015-12-24; view: 112


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