Geography 316 Biogeography Dr. B.A. Holzman SFSU...

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Patterns of DistributionI. Species Niche II. Distribution Patterns

Continuous/Cosmopolitan Disjunct DistributionsEvolutionary Relicts

Climatic Relicts Ecological Tolerance

Eurytopic vs StenotopicIII. Endemism

Neoendemics Paleoendemics

IV. DispersalOvercoming Dispersal Barriers Corridors/Filters/Sweepstakes Disharmonic distribution

Niche: lifestyle of a species includes: habitat, food, foraging route, season of activity, interaction with other species

Distribution: where organisms are and why includes range and extent of influence

Scale: world, habitat, microhabitat

Barriers: restrictions, limitations because of conditions: lack of food, water, shelter.. physical resources that will limit survival (can be "limiting factors")

Barriers can be climatic, topographic or a combination ex. water: barrier to terrestrial animals

land : barrier to marine organisms mtn. ranges:

other barriers: rainfall, light intensity, frost Tropical Distribution of the palm family, Arecaceae.Primary limiting factor is low temperature, few can tolerate freezing, none can withstand extreme cold.

Geography 316 Biogeography Dr. B.A. Holzman SFSU @2005

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Distribution Patterns

Continuous Distribution : area occupied by groups consists of a single region or a number of regions adjacent to one another (usually explained by climatic or biotic factors) ex. shrew

Discontinuous Distribution: area occupied by group is not continuous

• Eurytopic: ecologically tolerant/ highly efficient dispersal mechanisms ex. plantain Vespertionidae (bat family)

• Stenotopic: very specific preferences and limited ecological tolerance ex. damsel fly

Cosmopolitan Distribution: distribution of organisms found on all continents; broad habitat preferences

Circumboreal Distribution: around the northern regions. distribution of organisms possibly representing the past movements of continents

Distribution: Cosmopolitan

Distribution: Cosmopolitan Continuous Distribution


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Northern hawk owl

Circumboreal distribution

Other continuous distributions

Disjunct Distribution: discontinuous pattern -- areas occupied are widely separated or scattered over a particular continent or the world.

Such a pattern may represent....Evolutionary or Climatic Relicts

Disjunct Distribution

Evolutionary relicts: once dominant and widespread, but not able to compete with newer life forms.

ex. Magnolias

Distributions: Disjunct Process: Evolutionary Relict


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Climatic relicts or Habitat relicts: affected by past changes in climate, glaciations or sea level or geologic separation due to plate tectonics ex. Tulip tree, gorilla , carabidae

Disjunct :Relicts Disjunct Distributions:

Process:Climatic Relict

Mountain gorilla

Lowland gorilla

DISJUNCT DISTRIBUTION

DISJUNCT DISTRIBUTION Endemic OrganismsENDEMIC: a taxon native to a particular place and restricted to that geographic area specified, such as a lake, continent, biome or island (organisms confined to the areas where they evolved)

Two major reasons /factors influencing the degree of endemism in an area 1) isolation 2) stability


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Neoendemics: may be endemic only due to restricted time to expand range

Paleoendemics: ancient endemics, old species that have been restricted

Dispersal

• Dispersal: movement of individuals from a location within their species’ geographical range to an area outside of that range.

The Importance of Dispersal• Dispersal is a biogeographic process that is

part of the life history of every species, it is an important part of the process of evolution.

• Dispersal is effected by ecological factors which limit distribution of plants and animals –climate, substrate, biotic factors, and historical factors.

• Without dispersal, genetic interchange is limited

Dispersal Basics• To disperse is “to scatter or

distribute in various direction”

• Diffusion is the gradual movement of populations across suitable terrain that promotes a uniform density of individuals in the region

• Jump dispersal is the movement of individuals across great distances followed by successful establishment

Dispersal Basics• Long-distance, jump, or waif

dispersal– Dispersal across a

biogeographical barrier– Example: Bird flying to an

oceanic island– Explains disjunct

distributions and colonization patterns on oceanic islands

• Diffusion– Movement of a population

across a geographical area

– Example: Pine trees moving north after glacial retreat


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Modes of dispersal• Passive vs. Active

Wind, raft, birds, larval dispersal, migrating islands, agriculture or anthropogenic

Animals: walking, swimming, flying

Plants: eaten by animals, wind blown, agriculture

Dispersal• Anemochores:

dispersed by wind• Hydrochores:

dispersal by water– Anemohydrochores

• Zoochores: dispersed by animals

• Anthropochores: dispersed by humans

Plant dispersal Dispersal Routes

Corridors:

Filters:

Sweepstakes:

Dispersal RoutesCorridors: pathways or easiest route,

includes a wide variety of habitats, very little trouble traversing the corridors, two ends are almost identical in their biota

Filters: more limited variety of habitats, allows only certain animals to get through

European starling


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Sweepstakes: occasional arrivals: areas isolated and organisms get across by luck, attached to log/plant material, wind blown, etc.

Disharmonic distribution: biota only contains species with good dispersal mechanisms and has no species with poor dispersal capabilities

Disharmonic distribution

At one time the black-footed ferrets range extended from southern Canada through the 12 Great Plains States:Montana, Wyoming, eastern Utah, Colorado, Arizona, Texas, Oklahoma, Nebraska, Kansas, New Mexico, North Dakota, and South Dakota, and on into northern Mexico (Anderson 1972),


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The species, Bradypus variegatus, is endemic to the tropical and subtropical regions of the American continent (Grasse 1955).


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Continental Drift• Plate Tectonics and

Continental Drift: evidence for drift -- the distributions, past and present, of organisms – Drifting of continents

from 250mya to present: Pangaea, Gondwanaland, Laurasia

– the importance of drift: enhances speciation, changes climate

Conclusion• Organisms separated by great physical barriers are

can be quite different, despite having similar physical environments

• Distribution patterns lead many to infer about dispersal process

• There are limitations of dispersal as an explanatory vehicle: species-area relationships, spatial affinity

• A comprehensive approach to dispersal of taxa needs to be inclusive of geologic hypothesis, existing and past distributions, relationship among species to areas and evolutionary information


Geography 316 Biogeography Dr. B.A. Holzman SFSU...

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