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Biomes • Definition: a major geographic region defined on the basis of dominant plant growth forms. • Determinants: 1) Climate- particularly temperature and rainfall patterns; 2) Topography (landforms) and soils (edaphic factors): factors that secondarily influence the local distribution of organisms within biomes. • Climatic zones: 1) boreal (mean <5ºC), 2) temperate (mean >5, <20 ºC), 3) tropical (mean >20ºC). • The biome concept applies best to terrestrial systems. Grouping Characteristics • Plants and animals from different parts of the world often show similar characteristics if they are part of the same biome (character convergence). • The catbird (upper right) of North America and the reedwarbler (lower right) of southeast Asia are ecologically equivalent species. • They also show similar physiological adaptations. • Plants further show similar growth forms. Principal Biomes Tundra: 1) 2) 3) 4) 5) Climate- polar Vegetation- treeless, low evergreen shrubs, herbs and lichens Limiting factor- permafrost Distribution- far northern hemisphere and alpine zones Animals- polar bear (right) Principal Biomes Boreal Forest (Taiga): 1) 2) 3) 4) 5) Climate- cool summer, long, cold winter Vegetation- evergreen and deciduous conifers Limiting factor- short growing season (10 weeks) Distribution- northern hemisphere and alpine zones Animals- blue-headed vireo (right). Principal Biomes Temperate Grassland (Prairie): 1) 2) 3) 4) 5) Climate- hot summer, cold winter (continental climate) Vegetation- grasses and forbs; trees along rivers (riparian forest) Limiting factor- annual rainfall about 10” Distribution- centers of continents Animals- bison (above), prairie dog (left) Principal Biomes Temperate Seasonal Forest: 1) 2) 3) 4) 5) Climate- moderate; winter mean >-20ºF Vegetation- deciduous trees Limiting factor- 17 week growing season Distribution- eastern North America, western Europe, Korea Animals- red-spotted newt (right) Principal Biomes Temperate Rainforest: 1) 2) 3) 4) 5) Climate- mild and wet Vegetation- large conifers Limiting factor- summer rain and fog Distribution- Pacific northwest, New Zealand, S. South America Animals- ruby-crowned kinglet Principal Biomes Shrubland (Chaparral): 1) 2) 3) 4) 5) Climate- summer drought, rainy winter Vegetation- waxy-leaved, evergreen shrubs Limiting factor- frequent fires Distribution- S. California, Mediterranean, S. Australia Animals- western tanager (left) Principal Biomes Subtropical Desert: 1) 2) 3) 4) 5) Climate- very dry, high daytime temperature Vegetation- sparse, with drought-resistant leaves Limiting factor- heat, dryness Distribution- southwestern North America, central Africa, central Asia Animals- spadefoot toad (left) Principal Biomes Tropical Savannah: 1) 2) 3) 4) 5) Climate- rainy summer, dry winter Vegetation- grasslands with park-like stands of trees Limiting factor- limited rainfall Distribution- Mexico, S. Africa, SE Asia, N. Australia, E. S. America Animals- burrowing owl (right) Principal Biomes Tropical Rainforest: 1) 2) 3) 4) 5) Climate- uniform hot, wet and dry seasons Vegetation- diverse tropical hardwoods and vines Limiting factor- heavy rainfall and uniform high temperatures Distribution- N. S. America, W. Africa, SE Asia Animals- fruit dove (right) Alpine Zonation • Increasing altitude mimics the effects of increasing latitude. • At higher altitudes in mountains, more northerly associated biomes are found. • In the northeast, the lowest elevations of mountains have temperate seasonal forest, which is replaced by boreal forest at higher elevations, which is in turn replaced by alpine tundra. • Near tree line (the highest elevation of tree growth), a stunted boreal forest called krummholz develops. • Alpine biomes differ from latitudinal biomes in factors like day length and temperature variation. Global Biome Distribution Climatic Relationship of Biomes