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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