Ecosystem Ecology: Terrestrial Ecosystems

Test 3

Ecosystem

is the biotic community and its abiotic environment, functioning as a system

• lake

• forest

• tundra

• tropical rainforest

ecosystem ecology

the study of natural systems with emphasis on energy flow and nutrient cycling

primary productivity

is the rate at which autotrophs convert carbon dioxide (in the atmosphere or water)into organic compounds 

gross primary productivity (GPP) 

total rate of photosynthesis (energy assimilated) by autotrophs 

net primary productivity (NPP)

rate of energy storage as organic molecules after energy is expended for cellualr respiration (R)

what are the primary controls on net primary productivity in terrestrial ecosystems

climate and nutrient availability

• temperature

• water availability

• nutrient availability

Warm + Wet =

high NPP

• plants can photosynthesize quickly and have enough water

warm + dry =

low NPP

• warm temperatures increase water demand but lack of water limits growth

Cold = 

Low NPP (regardless of water) 

• low temperatures slow down photosynthesis and growth 

why do plants with longer seasons have more time to photosynthesize and produce biomass

they have higher plant productivity

what does more available nutrients indicate

higher NPP

Nutrients affect NPP, but where do they come from?

• come from the atmosphere or rocks

• enter soil or water and are absorbed by plants

• stored in the bodies of living organisms

• return to soil as dead organic matter, feeding decomposers

nutrient cycling

includes the mineralization of organic nutrients by microbial decomposers

these minerals are then available for the autotrophs to take up and use to build new tissues

key decomposers

fungi and bacteria

mites/springtails

millipedes and earthworms

what are decomposers influenced by

quality of litter/OM

soil/sediment properties (pH)

climate (temperature and precipitation)

Biomes 

biotic units that are classified by predominant plant types 

• at least 8 major terrestrial 

tropical rainforest

biome

• restricted to the equatorial zone

• warm and wet year-round

• high NPP

• tall broadleaf evergreen trees, dense vegetation

• high diversity of plant and animal life

• Most nutrients are stored in the living plants, not in the soil

• cover less than 2% of earth surface

• home to 50% of all terrestrial species

• most diverse and productive terrestrial ecosystem

Types of plant growth in rain forest

climbing vine

epiphytes

strangler figs

buttresses 

Tropical Savanna

Biome

• warm, semiarid regions with season rainfall (wet+dry season)

• moderately high NPP

• grasses with scattered drought-resistant shrubs and trees

• fire-maintained ecosystem

• large diversity of herbivores that graze or browse on the vegetation

• support large numbers of incests, carnivores, and scavengers

• two layer bertical structure of grasses and trees or shrubs

how do trees in savannas create microenvironments that support biodiversity than the surrounding grasslands

soil is richer due to leaf litter and nutrients

shaded ground is cooler

soil holds more moisture

Temperate deciduous forest

Biome

• moderate temp + rainfall; four seasons

• broad leaf deciduous trees dominate

• rich soils and understory pf shrubs, ferns and wildflowers

• moderate NPP

• seasonal changes affect plant growth and animal behavior

four vertical layers in deciduous forests

canopy

understory

shrubs

floor

Temperate grasslands

Biome

• moderate temperature with low precipitation

• often experience drought as they occur in regions where annual precipitation is reduced as air masses move inland

• low to moderate NPP

• dominated by herbivorous species; insects, large grazers, burrowing animals

• productivity is related to precipitation

what did grasslands evolve under

selective pressure of grazing

Strata in grasslands

herbaceous plants

ground cover

below-ground root layer

• can make up more than half of the plant biomass and extends deep into the soil

Shrub lands

Biome

• hot, dry summers + cool, wet winters

• soils are generally deficient in nutrients 

• plants are adapted to fire and low nutrients 

• moderadte NPP

• home to drought-tolerant animals

Sclerophyllous

type of plant characteristic of shrub lands

• have thick, tough, and leathery leaves with a waxy coating that helps reduce water loss

deserts 

biome 

• very low precipitation. can be hot or cold 

• high evaporation rates (extremely dry conditions) 

• plants and animals have adaptions to very arid climates 

• low NPP

hot deserts

range from those lacking vegetation to ones with some combination of herbs, dwarf shrubs, and succulents. Animals avoid heat and conserve water (kangaroo rat - gets water from seeds, never drinks)

cold deserts

range from vegetation dominated by sagebrush, shade scale, woody shrubs, and grasses adapted to cold, dry conditions. Animals conserve heat and survive long dormant seasons. (bighorn sheep - thick, insulated coat, can go long time periods without drinking)

Boreal Forest (taiga)

Biome 

• cold, long winters, short summers. 6-7 weeks warm enough to photosynthesize

• dominated by evergreen conifers, needles prevent water loss, conical shade sheds snow 

• primarily occupies formerly glaciated land 

• low NPP 

• has a unique community of herbivores (caribou, moose, snowshoe hare, red squirrels, and porcupine) and predators (wolf, lynx, pine martin, and owls)

Tundra

Biome

• very cold, very low precipitation

• dominated by small shrubs, grasses, herbs, mosses, and lichens

• low animal diversity, dominant vertebrates are herbivores

• very low NPP

• simple vegetation structure with few species and slow growth (Only species that can withstand constant soil disturbance, buffeting by the wind, and abrasion by wind-carried particles of soil and ice can survive. Arctic plants propagate almost entirely by vegetative means)