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THE DISTRIBUTION OF THE DISTRIBUTION OF COMMUNITIESCOMMUNITIES
Biogeographic PerspectivesBiogeographic Perspectives
• Ecological Communities - complex associations of species
• To what extent are species distributed together as interdependent communities as opposed to being distributed essentially independently of one another?
Biogeographic PerspectivesBiogeographic Perspectives
• Life zones, Ecoregions or Biomes - specific kinds of animals and microorganisms are associated with specific vegetation formations associated with particular climates
Communities and EcosystemsCommunities and Ecosystems
• Definitions –– Community– Community structure– Community function– Ecosystem – Microcosm – Biosphere
Communities and EcosystemsCommunities and Ecosystems
• Definitions -
• Community -consists of those species that live together in the same place
Communities and EcosystemsCommunities and Ecosystems
• Community structure - static properties including diversity, composition, and biomass of species in a community
Communities and EcosystemsCommunities and Ecosystems
• Community function - all the dynamic properties and activities that affect energy flow and nutrient cycling
Communities and EcosystemsCommunities and Ecosystems
• Ecosystem - includes all the species inhabiting a place as well as all the physical features of the physical environment
Communities and EcosystemsCommunities and Ecosystems
• Microcosms - small, relatively self-contained ecosystems
Communities and EcosystemsCommunities and Ecosystems
• Biosphere - largest and only complete ecosystem -> encompasses the entire earth
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Basal metabolic rate - varies with body mass
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Body mass - most important variable to measure –> larger the organism the more energy it requires for maintenance, growth and reproduction
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Larger animals have greater reserves and therefore greater potential to withstand prolonged stresses such as starvation, dehydration, and subfreezing temperatures
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Smaller organisms require fewer resources per individual than large ones, use smaller areas, can be more specialized, and still maintain population densities high enough to avoid extinction
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Any geographic area contains a greater number of small-bodied species than large ones
AND
• Large organisms are constrained to have broad geographic ranges
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Trophic Status - influences role in the community structure
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Ecological Pyramids - successively higher trophic levels tend to have less than 10% the rate of energy uptake of the level below them, and usually contain proportionately lower biomass and fewer individuals and species
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels
• –> predictable characteristics that affect ecological roles and geographic distributions
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels
• –> predictable characteristics that affect ecological roles and geographic distributions
• –> fewer species of carnivores than herbivores
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels• –> predictable characteristics that affect
ecological roles• and geographic distributions• –> fewer species of carnivores than herbivores• –> tend to feed on several species
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels• –> predictable characteristics that affect
ecological roles• and geographic distributions• –> fewer species of carnivores than herbivores• –> tend to feed on several species• –> broad habitat requirements
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Carrying Capacity - (measured in units of usable energy)
• –> lower for successively higher levels• –> predictable characteristics that affect ecological roles• and geographic distributions• –> fewer species of carnivores than herbivores• –> tend to feed on several species• –> broad habitat requirements• –> wide geographic distributions• (Ex: Mountain lion, Puma concolor)
Community Organization : Community Organization : Energetic ConsiderationsEnergetic Considerations
• Productivity varies greatly among different habitats–> widespread highly productive habitats such as rainforests and coral reefs have higher diversity ofspecialized species–> small, isolated areas (such as small islands) andwidespread unproductive habitats (such as borealforests and tundra) contain fewer specialized speciesand more generalized species
Terrestrial BiomesTerrestrial Biomes
• Terrestrial communities are classified on the basis of the structure of the vegetation
Terrestrial BiomesTerrestrial Biomes
• Observed that similar climate regimes do tend to support• structurally and functionally similar vegetation in disjunct• areas throughout the world • –> these similarities may result from convergence • –> unrelated plant species in geographically isolated• regions have evolved similar forms and similar• ecological roles under similar selective pressures
Terrestrial BiomesTerrestrial Biomes
• Six major forms of terrestrial vegetation recognized:
• 1.) Forest • 2.) Woodland • 3.) Shrubland • 4.) Grassland • 5.) Scrub • 6.) Desert
Terrestrial BiomesTerrestrial Biomes
• 1.) Forest - a tree-dominated assemblage with a fairly continuous canopy
Terrestrial BiomesTerrestrial Biomes
• 2.) Woodland - a tree-dominated assemblage in which individuals are widely spaced, often with grassy areas or low undergrowth between them bare
Terrestrial BiomesTerrestrial Biomes
• 3.) Shrubland - a fairly continuous layer of shrubs, up to several meters high
Terrestrial BiomesTerrestrial Biomes
• 4.) Grassland - an assemblage dominated by grasses and forbes
Terrestrial BiomesTerrestrial Biomes
• 5.) Scrub - a mostly shrubby assemblage in which individuals are discrete or widely spaced
Terrestrial BiomesTerrestrial Biomes
• 6.) Desert - an assemblage with very sparse plant cover in which most of the ground is bare
Terrestrial BiomesTerrestrial Biomes
• Twelve common terrestrial biomes are recognized– correspond to the distribution of climatic
zones– latitude and elevation reflect influence of local
climate and soil type
Terrestrial BiomesTerrestrial Biomes
• Tropical rain forest - richest and most productive
• covers approximately 6% of surface• approximately 50% of species• low elevations at tropical latitudes (10o N to 10o
S)• abundant rainfall (>180 cm annually)• rainfall tends to be seasonal• temperatures nearly uniform year-round (over
18o C)
Terrestrial BiomesTerrestrial Biomes
• Tropical rain forest (continued)–• dominant plants are large evergreen trees that
form a closed canopy (30 to 50m)• convergent morphology of trees (buttressed
bases, straight trunks, broad leaves with smooth edges)
• also characterized by lianas (woody vines) and epiphytes (orchids, ferns and New World bromeliads)
• very little light reaches the forest floor which is open and devoid of vegetation
Tropical rain forestTropical rain forest
Terrestrial BiomesTerrestrial Biomes
• Tropical deciduous forest - occur in hot lowlands outside the equatorial zone (between 10o and 30o latitude)
• rainfall is more seasonal• dry season is more pronounced• canopy is low and more open• trees and shrub shed their leaves during the dry
season• flowering and fruit maturation occurs during the
dry season
Tropical deciduous forestTropical deciduous forest
Synchronous blooming at the start of the dry season
Madagascar
Puerto RicoCeiba trees in Ecuador
Terrestrial BiomesTerrestrial Biomes
• Thorn woodland - tropical and subtropical • hot semiarid lowlands • small spiny or thorny shrubs and trees are the
dominant form• Members of the genus Acacia are common on
all continents• succulents such as cacti (Cataceae) in the New
World and convergent forms of Euphorbia (Euphorbiaceae) in Africa are common
• often found on drier sites adjacent to tropical deciduous forests
Terrestrial BiomesTerrestrial Biomes
• Tropical savanna - dominated by a nearly continuous layer of xerophytic grasses and sedges and scattered with fire-resistant trees and shrubs
• low to intermediate elevations at intertropical latitudes (between 25o N and 25o S)
• one or two rainy seasons followed by intense droughts
• weather patterns driven by seasonal shifts in the Intertropical Convergence Zone
Terrestrial BiomesTerrestrial Biomes
• Tropical savanna (continued) - • annual rainfall varies from 30 to 160 cm• 3 common factors:• 1) seasonally intense precipitation • 2) fire during the dry season• 3) migratory or seasonal grazing• intertropical Africa (most extensive savannas) • support the most diverse community of large
grazing mammals in the world
Tropical SavannaTropical Savanna
Africa
Australia
Terrestrial BiomesTerrestrial Biomes
• Desert - hot deserts and semideserts occur around the world at low to intermediate elevations
• --> especially in belts of dry climates (30o to 40o N and S)
• --> rain is seasonal and unpredictable (often less than 25 cm per year)
• --> amount of rainfall is less than the evaporative potential
DesertDesert
Terrestrial BiomesTerrestrial Biomes
• Sclerophyllous woodland (and Chaparral) - mild temperate climates
• --> moderate winter precipitation
• --> long, usually hot, dry summers
• --> broad variety of xeric woodlands (Ex. - Pinon-juniper, sandhill pine woodlands, pine flatwoods)
ChaparralChaparral
King Sugar Bush
Californis Blue Oak, Iron Oak Aardwolf
Terrestrial BiomesTerrestrial Biomes
• Sclerophyllous woodland (continued) -
• --> dominant plants have sclerophyllous (hard, tough, evergreen) leaves
• --> can receive up to 100 cm rain per year
• --> areas that receive less than 60 cm of rainfall per year have low, shrubby vegetation -> Sclerophyllous scrubland (Chaparral)
Terrestrial BiomesTerrestrial Biomes
• Subtropical evergreen forest - also called Oak-laurel forests or Montane forests
• --> common in subtropical mountains at intermediate elevations
• --> China, Japan, disjunct areas of the Southern Hemisphere and southeastern U.S.
• --> most dominant species are dicotyledons with broad, sclerophyllous evergreen leaves (Ex. - laurels, oaks, and magnolias)
Terrestrial BiomesTerrestrial Biomes
• Temperate deciduous forest - temperate latitudes
• --> also called Summer-green Deciduous Forests
• --> variable in their structure and composition across eastern North America, western Europe, and parts of eastern Asia
Temperate deciduous forestTemperate deciduous forest
Terrestrial BiomesTerrestrial Biomes
• Temperate rain forest - uncommon, found along the western coast of continents where precipitation exceeds 150 cm per year and falls during 10 months of the year
• --> cool temperatures predominate year round• --> always above freezing• --> epiphyte diversity is high consisting of
mosses, lichens, epiphyllous fungus and some ferns
• --> renowned for world’s oldest and largest trees
Temperate rain forestTemperate rain forest
Terrestrial BiomesTerrestrial Biomes
• Temperate grassland - situated geographically and climatically between the deserts and the temperate forests
• --> most extensive in the interior plains of the Northern Hemisphere
• --> markedly seasonal, substantial annual variation in temperature and rainfall
• --> vegetation dominated by grasses, sedges, and other herbaceous plants (single stratum)
• --> tall grasslands to shortgrass plains• --> vegetation growth is stimulated by fire and grazing
Temperate GrasslandTemperate Grassland
Terrestrial BiomesTerrestrial Biomes
• Boreal forests – “swamp forest”, broad band across northern North America, Europe, and Asia in regions of cold temperatures
• --> extends southward into temperate latitudes at high elevations (i.e., into southern Mexico)
• --> dominated by a few species of coniferous trees (Ex. - spruce and firs)
Terrestrial BiomesTerrestrial Biomes
• Boreal forests (continued) -• --> decomposition rates are slow because of
cool temperatures and waterlogged soils• --> results in the accumulation of peat and humic
acids• --> soil nutrients unavailable for plant growth• --> acidic soils and cool temperatures limit
diversity and productivity
Boreal forestsBoreal forests
Terrestrial BiomesTerrestrial Biomes
• Tundra - treeless biome found between the boreal forests and the polar ice caps
• --> also at high elevations on tall mountains (Alpine tundra)
• --> temperatures below freezing for at least 7 months of the year
• --> precipitation less than many deserts• --> soils more nutrient poor than boreal
forests environment
Terrestrial BiomesTerrestrial Biomes
• Tundra (continued) -• --> single, dense stratum of vegetation• --> high productivity during short growing
season• --> heavily grazed by migratory mammals
such caribou (Rangifer tarandius), muskox (Ovibus moshatus) and Dall sheep (Ovis dalli)
• --> fragile environment
TundraTundra