Characterize major terrestrial biomes by climate, explain why biodiversity contributes to ecosystem stability, and describe documented human impacts on ecosystems.
Major terrestrial biomes are distinguished mainly by temperature and precipitation patterns: tropical rainforest (consistently hot and wet year-round, the most biodiverse biome on Earth, with a distinctly layered canopy structure); desert (extreme water scarcity, organisms adapted to conserve water and tolerate large daily temperature swings); grassland (moderate, seasonal rainfall, too little to reliably support forest, dominated by grasses and grazing animals); temperate forest (four distinct seasons, moderate rainfall, often deciduous trees that drop leaves in autumn); taiga, or boreal forest (long, cold winters, dominated by cone-bearing evergreen trees); and tundra (extremely cold, with a permanently frozen subsurface layer called permafrost and a very short growing season). Aquatic biomes, freshwater and marine, actually cover most of Earth's surface and are organized more by light penetration, depth, and salinity than by the temperature-and-precipitation logic that defines terrestrial biomes.
Biodiversity, the variety of species within an ecosystem, generally increases that ecosystem's stability and resilience, since a more diverse food web has more alternative paths for energy to flow through if any single species is lost or declines -- species richness, simply the number of different species present, is one straightforward way to measure it. Human activities have a number of well-documented ecological effects, stated here factually rather than as argument: habitat destruction and fragmentation reduce the space and connectivity available to wild populations; invasive species introduced outside their native range can disrupt existing food webs that never evolved alongside them; pollution and overharvesting directly reduce specific populations; and climate change is measurably shifting biome boundaries and the geographic ranges of many species. In response, conservation approaches in active use include protected areas, habitat restoration projects, and regulated, sustainable harvesting limits.
Mastery looks like: They can characterize at least four biomes by climate and adaptation, explain why biodiversity increases ecosystem stability, and describe a documented human impact alongside a real conservation response.
Common stumbles: Confusing biomes that share a similar temperature or precipitation feature, like grassland and temperate forest; treating "biodiversity" as a vague feel-good word rather than the measurable concept, species richness, defined this week.