biogeo lec 5 the distribution of communities

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

• Definitions -

• Community -consists of those species that live together in the same place

• Community structure - static properties including diversity, composition, and biomass of species in a community

• Community function - all the dynamic properties and activities that affect energy flow and nutrient cycling

• Ecosystem - includes all the species inhabiting a place as well as all the physical features of the physical environment

• Microcosms - small, relatively self-contained 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

• Body mass - most important variable to measure –> larger the organism the more energy it requires for maintenance, growth and reproduction

• Larger animals have greater reserves and therefore greater potential to withstand prolonged stresses such as starvation, dehydration, and subfreezing temperatures

• 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

• Any geographic area contains a greater number of small-bodied species than large ones

• Large organisms are constrained to have broad geographic ranges

• Trophic Status - influences role in the community structure

• 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

• 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

• –> 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

• –> 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

• –> 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)

• 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

• 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

• Six major forms of terrestrial vegetation recognized:

• 1.) Forest • 2.) Woodland • 3.) Shrubland • 4.) Grassland • 5.) Scrub • 6.) Desert

• 1.) Forest - a tree-dominated assemblage with a fairly continuous canopy

• 2.) Woodland - a tree-dominated assemblage in which individuals are widely spaced, often with grassy areas or low undergrowth between them bare

• 3.) Shrubland - a fairly continuous layer of shrubs, up to several meters high

• 4.) Grassland - an assemblage dominated by grasses and forbes

• 5.) Scrub - a mostly shrubby assemblage in which individuals are discrete or widely spaced

• 6.) Desert - an assemblage with very sparse plant cover in which most of the ground is bare

• Twelve common terrestrial biomes are recognized– correspond to the distribution of climatic

zones– latitude and elevation reflect influence of local

climate and soil type

• 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)

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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)

• 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)

• 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

• 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

• 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

• 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)

• 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

• 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

• 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

biogeo lec 5 the distribution of communities

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ecosystems community

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