Chapter 4

Terrestrial Biomes & Aquatic Ecosystems

Terrestrial biomes Named for predominant vegetation Also have characteristic animals

Boundaries? No sharp boundaries between biomes Intergrades

Importance of climate Prevailing climate is most important factor

in determining what kind of biome will develop Precipitation, temperature are most important

Desert biomes <10 inches (<25.4 cm) of rain per year Cool Temperate Tropical

Grassland biomes 10-30 inches (25.4-76.2 cm) of rain per

year Tundra Temperate grassland Tropical savanna

Forest biomes >30 inches (>76.2 cm) of rain per year Taiga or coniferous forest Temperature deciduous forest Tropical rain forest

Aquatic ecosystems Initial categories based on salinity

Freshwater Marine Estuary

Freshwater - nonmoving Standing waters

Lakes Ponds

Significant stratification in community structure Light Temperature

Freshwater - moving Moving waters Rivers Streams Communities change from headwaters

(source) to mouth as environment changes

Headwaters vs. mouth Headwaters

Cool High current velocities Few nutrients

Mouth Warmer Slower More turbid More nutrients

Marine Vertical and horizontal changes

Light Temperature Nearshore Open ocean

Estuary Freshwater rivers merge with oceans

Mixing zone Very high productivity Threatened by pollution

Climatograph

Climograph Temperature, precipitation not sole

determiners Overlap among different biomes on plot

suggests that other factors also are important Seasonality of precipitation Temperature fluctuations around mean Soil composition (based on geology)

Deserts Lands where evaporation exceeds rainfall High evaporation rate

7-50X precipitation

Deserts Occur in 2 distinct belts between 15-35° N

& S latitude Result primarily from worldwide

circulation of air masses (dry over deserts) ~25% of world’s land mass

True deserts <10 inches of rain per year

Semi-deserts may have 2-3X that, but have high evaporation rates

Low humidity results in very hot days, but cool or cold nights

Life is keyed to rainfall events Infrequent, but usually heavy when they

occur

Desert life Plants, animals are either drought evaders

or drought resistors

Evaders Plants survive dry periods as seeds, but

germinate, grow, and reproduce after rainfall Animals may hibernate (cold) or estivate (hot)

Dormancy during dry period E.g., spadefoot toad emerges to reproduce in pools

formed after rain

E.g., birds migrate in and out

Resistors - plants Plants develop deep roots to become

independent of rainfall events (woody shrubs) or are succulents to store water in stems (cactus)

Resistors - animals Behavioral adaptations Come out only at night - spiders, scorpions,

rodents, predators

Resistors - animals Physiological adaptations No need to drink

Kangaroo rate with super kidneys gets all water from seeds

Grasslands Tropical savannas - grasslands with

scattered individuals trees Central S. Amer., Central & S. Africa

Savannas 3 distinct seasons Cool-dry, hot-dry, warm-wet Frequent fires suppress trees, maintain

grasses and forbs Herbaceous, low-growing annuals &

perennials (dicots) Regrow from roots or seeds every year

Savannas Large herbivores (zebras, giraffes) and

burrowing animals most common Most active during the rainy season

Temperate grasslands Similar to tropical savanna, but occur in

cooler regions N. Amer. prairie (French for plains) Russian steppe Hungarian pusztas S. Amer. pampas African veldt

Temperate grasslands At one time covered 42% of world land

surface Much under cultivation today Excellent soils

Rich topsoil layer

Temperate grassland climate High rates of evaporation Periodic severe drought Rainfall ~25-75 cm/year Too light to support forest, but too heavy to

encourage desert

Temperate grassland grasses Sod-forming

Kentucky bluegrass Bunch grasses

Big, little bluestem

Temperate grasslands Most require periodic fires for

maintenance, renewal, elimination of incoming/invading woody growth

Animal life dominated by grazing and burrowing species

Tundra Northernmost limits for plant growth, and

at high altitudes Plants generally low-growing

Mat or shrubby

Arctic tundra Encircles north pole

Brief warm summers with nearly 24 hrs of sun/day

Presence of permafrost Water-logged soils - low evaporation Shrubs, sedges grasses, mosses, lichens

Alpine tundra At high elevations at all latitudes Variable daylength, many of the same

restrictions, plant species

Tundra animals Migratory, well-suited for cold climate

Musk oxen, caribou, reindeer Lemmings, white fox, snowy owl

Tropical forests Equatorial, mean temp. ~25°C, 12 hrs

sunlight per day Rainfall highly variable-determines type of

tropical forest present

Types of tropical forests Thorn forests - furthest from equator,

prolonged dry season

Tropical deciduous forest More rainfall nearer equator, distinct wet,

dry seasons Lose leaves during dry seasons

Types of tropical forests

Tropical rain forest >250 cm of rain per year Perpetual midsummer conditions Uninterrupted plant growth

Types of tropical forests

Tropical rain forests Contain as many species of plants and

animals as all other types of ecosystems combined

4 mi2 area - 750 species of trees, 1500 species of flowering plants

Tropical rain forests Typically stratified into 5 layers

Each layer has characteristic plants, animals

May reach height of 80 m

Tropical rain forest soil Very poor - little or no topsoil Easily weathered Subsoil with iron-based clay - laterite Major problems with slash-and-burn

agriculture

Tropical rain forests today Deforestation

Deforestation Loss of forests at present rate will mean

disappearance within next 15-25 years Major problems will result from climate

change, loss of species of medicinal, economic importance

Temperate deciduous forest Eastern N. Amer, N. Europe and east Moderate temps., moderate moisture levels

5-6-month growing season

Temperate deciduous forest Dominated by broad-leaved deciduous

trees Relatively nutrient-rich soil provides for

good growth Typically have 4 layers present

Ground, shrub, sapling, canopy Rich diversity of plant, animal life

Taiga Boreal forest, coniferous forest

Harsh winters with lots of snow

Taiga Dominated by conifers - spruce, pine, fir,

hemlock

Best suited for short growing season because they are not deciduous Can carry out photosynthesis whenever temps. rise

above freezing Needle shape, waxy cuticle conserve moisture

Thin, acidic, develop slowly Pine needles break down slowly in cool

climate

Taiga soils

Taiga animals Primarily seed, insect eaters, or those that

feed on plants in or near water Squirrels, birds, elk, moose, deer, beaver,

porcupine, grizzlies, wolves

Standing freshwaters Lakes and ponds

Standing freshwaters Significant stratification in community

structure Light

Photic zone Phytoplankton, zooplankton

Aphotic zone Detritus, decomposers

Moving freshwaters Longitudinal zonation in physical,

chemical characteristics

Change in producers, benthic (bottom dwelling), fish assemblages

Marine 3/4 of world’s surface, major impact on

climate, wind patterns, algae supply most of world’s oxygen

Marine

Marine Photic, aphotic zones (vertical) Intertidal, neritic, oceanic zones (horiz.)

Intertidal-wetted, dried from tides Neritic-shallow regions over continental shelves Oceanic-beyond shelves - deep zones

Pelagic-open water Benthic-sea floor

Abyssal zone-deep benthic - cold, high water pressure, no light

Deep sea fishes

Estuary Freshwater rivers merge with oceans

Estuary Not very diverse - few species tolerant of

salinity Very productive - oysters, crabs, fish,

waterfowl Most in danger from water pollution