BIOGEOGRAPHIC DISTRIBUTION CONTROLS

A. INTRODUCTION

Biogeography: study of the geographic distribution of biological organisms

Map of global biome patterns:
Image credit: U.S. Department of Agriculture Natural Resources Conservation Service (2005) World soil resources map index. http://soils.usda.gov/use/worldsoils/mapindex/index.html

Geographic range: the spatial extent of where an organism lives

• range may change over time due to:

  • successful colonization of new areas

  • extirpation and extinction

Ecological niche: the combination of conditions required for an organism to survive and reproduce

• food (energy & nutrients)

• habitat

• temperature, sunlight, moisture

• competition & predation

Influencing factors:

• dispersal & colonization

• abiotic influences: climatic tolerances (water, temperature, sunlight)

• biotic influences: competition, mutualism & commensalism

• disturbances & ecological succession

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B. DISPERSAL & COLONIZATION

• Find better habitat; avoid competition

• Accessibility

  • active & passive movement

• Colonization requires an available ecological niche & successful reproduction

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C. ABIOTIC INFLUENCES

• Moisture

• Temperature

  • photosynthesis rate

  • respiration rate



• Sunlight

• Soil nutrients

• Adaptations:

  • leaf characteristics

  • root characteristics

  • deciduous/evergreen habit

  • reproductive habits

  Image credit: Gary M. Stolz. U.S. Fish & Wildlife Service Digital Library System. http://images.fws.gov/default.cfm?library_id=none&CFID=3302570&CFTOKEN=37370443

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D. BIOTIC INFLUENCES

Competition: food, water, nesting space, ground space

• direct competition for resources

• indirect competition that doesn't allow other organisms to move in or survive

Mutualism: interactions between species that benefit both species

• e.g. plant roots provide carbohydrates for fungal mycorrhizae while the fungal mycorrhizae increase roots' ability to take up nutrients

• flowering plants & pollinators

Commensalism: one species benefits from a second species, but the second species is unaffected by the first

• e.g. epiphytes in tropical rainforests gain support and access to sunlight

Predation & parasitism: one organism benefits at the expense of another

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E. DISTURBANCES & ECOLOGICAL SUCCESSION

Disturbances: events that disrupt an ecosystem

wildfire common occurrence in boreal coniferous forests common occurrence in Mediterranean (Cs) climates (after summer drought) fuel load: litter & living organisms ignition most often due to lightning adaptations to survive fire; necessity of fire for reproduction wind, flooding   Image credit: U.S. Fish & Wildlife Service Digital Library System. http://images.fws.gov/default.cfm?library_id=none&CFID=3302570&CFTOKEN=37370443

Succession: directional change in the mix of plant & animal species occupying a particular area over time

time span: years, decades, centuries repeated colonization, establishment & extirpation of species pioneer community: first colonizers after a disturbance hardy species; fast-growing; short-lived often create conditions that favor other organisms simple community with low diversity easily disrupted Image credit: U.S. Forest Service Superior National Forest http://www.fs.fed.us/r9/forests/superior/storm_recovery/blowdown_images.php

• intermediate communities

• slower-growing species with longer life spans

• increasing diversity

• increasing stability

• late successional communities

  • relatively stable communities

  • diversity allows recovery from minor disturbances

• climax community: "end" of succession

• in reality, true climax communities rarely form due to the frequency of natural disturbances

• in reality, disturbances rarely affect entire ecosystems, rather they affect patches

• in reality, disturbances rarely set ecosystems back to square one

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F. SUMMARY

Factors influencing the geographic range of organisms include:

• availability of ecological niches

• ability to disperse to suitable habitats

• abiotic & biotic influences

• tolerance limits

• ecological succession