Week 11: Ecosystem Ecology

Ecosystem

All living and nonliving components in an area interacting together, including communities of organisms and their physical environment.

Relationship of ecosystem to populations and communities

Populations are groups of one species, communities are groups of interacting populations, and ecosystems include both communities + abiotic factors.

American Tallgrass Prairie

Ecosystem once covering central U.S.; 80% grasses, 20% flowers; depends on periodic fire and grazing; now only 4% remains due to agriculture.

Prairie biomass

About ¾ of plant biomass is below ground as roots, helping soil stability and nutrient storage.

Keystone species

A species with a disproportionately large impact on its ecosystem; removal causes major changes to other species.

Bison as keystone species

Their grazing prevents grass overgrowth and creates habitats for many species; their wallowing creates micro-habitats for plants and insects.

Bison as landscape engineers

They disturb soil and encourage plant diversity, similar to how beavers alter streams.

Prairie dogs as landscape engineers

Their burrowing aerates soil and provides shelter for other animals.

Bison population bottleneck

In the late 1800s they were hunted from 30 million to ~500 individuals, drastically reducing genetic diversity.

American Prairie Reserve (APR)

A rewilding project to restore 3.2 million acres of prairie and create the largest wild bison herd in the world.

Goal of APR

To reconnect habitats and restore native species like bison and prairie dogs to their historical range.

APR controversy

Some ranchers oppose it because it challenges traditional ranching practices and land use.

Nutrient cycles

Processes that recycle essential elements like nitrogen, phosphorus, and carbon through living and nonliving parts of ecosystems.

Nitrogen cycle

Nitrogen moves through soil, water, and air via decomposition, fixation, and absorption into proteins and DNA.

Phosphorus cycle

rock weathering and supports DNA, ATP, and bones in organisms.

Why nutrient cycles need functional ecosystems

Decomposers and diverse species are needed to keep nutrients flowing between living and nonliving systems.

Uneven earth temperature distribution

Because sunlight hits the equator more directly than the poles, creating climate zones.

Climate and biomes

Average temperature and precipitation determine plant life and thus define biomes.

Biome definition

A large region defined by its climate and dominant plant and animal life.

Eight major terrestrial biomes

Tundra, Taiga (boreal forest), Temperate deciduous forest, Temperate grassland, Mediterranean (shrubland), Tropical forest, Savanna, Desert.

Tundra

Cold temperatures, low precipitation, permafrost, low-growing plants.

Taiga

Cold forests of evergreens with long winters and short summers.

Temperate deciduous forest

Moderate rainfall and seasons; trees drop leaves in winter.

Temperate grassland

Moderate temperature, low rainfall, grasses dominate (North American prairies).

Mediterranean biome

Hot, dry summers and cool, wet winters; short shrubs and evergreens.

Tropical forest

Warm and wet all year; dense vegetation and high biodiversity.

Savanna

Warm climate with wet and dry seasons; grasses with scattered trees.

Desert

Very low precipitation; can be hot or cold; plants adapted for water conservation.

Why same biome in different places

Similar climate patterns create similar plant and animal adaptations even in geographically distant areas.

Water cycle

Water moves through evaporation, condensation, precipitation, and groundwater flow.

Ogallala Aquifer

Large underground water supply for Midwest agriculture; being depleted faster than it can recharge.

Rewilding

Restoring native species and natural ecosystem processes to let nature shape itself.