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Patterns of DistributionI. Species Niche
Ecological Tolerance Eurytopic vs Stenotopic
II. Distribution Patterns Continuous/Cosmopolitan Disjunct DistributionsEvolutionary Relicts
Climatic Relicts III. 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
• Eurytopic: ecologically tolerant/ highly efficient dispersal mechanisms ex. plantain Vespertionidae (bat family)
• Stenotopic: very specific preferences and limited ecological tolerance ex. damsel fly
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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• Barriers: restrictions, limitations because of conditions: lack of food, water, shelter.. physical resources that will limit survival; can be "limiting factors")
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.
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Sugar maple
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
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Continuous Distribution
The species, Bradypus variegatus, is endemic to the tropical and subtropical regions of the American continent (Grasse 1955).
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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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),
Cosmopolitan Distribution: distribution of organisms found on all continents; broad habitat preferences
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Distribution: Cosmopolitan
Distribution: Cosmopolitan
Northern hawk owl
Circumboreal distribution: around the northern regions. distribution of organisms possibly representing the past movements of continents
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Other continuous distributions
Distributions can also be defined by location
i.e. Central West African Distribution
• Disharmonic Distribution: a biota based on those groups with good dispersal capabilities
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Discontinuous Distribution: area occupied by group is not continuous
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. MagnoliasTulip trees
Distributions: Disjunct Process: Evolutionary Relict
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Disjunct Distributions:
Process: Evolutionary Relict
Climatic relicts or Habitat relicts: affected by past changes in climate, glaciations or sea level or geologic separation due to plate tectonics ex. gorilla , carabidae
Disjunct :Relicts
Climate relict• Dodecatheon: glacial relict
Dawn redwood: Pre glaciation
Geog 316 Fall 2006 SFSU Dr. B. Holzman
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Mountain gorilla
Lowland gorilla
Disjunct Distribution
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
DISJUNCT DISTRIBUTION
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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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
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Kangaroo rat
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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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
Neoendemics• Neoendemics are found frequently in geologically youthful habitats, and
often their rarity is partly a function of their youth - in some cases these plants have not had time to expand their range from their point of origin to their climatic and geological limits.
Oenothera californica
Limnanthes floccosa
Paleoendemics• Carpenteria californica, Lyonothamnus floribundus, Pinus radiata,
P. torreyana, and Sequoiadendron gigantea are paleoendemicsthat were once more broadly distributed, but have retreated to their current ranges in response to dramatic climatic change.
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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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
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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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
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
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Plant dispersal
Physical Barriers can be climatic, topographic or a combination
ex. water: barrier to terrestrial animals land : barrier to marine organisms mtn. ranges:
Dispersal Routes
Corridors:
Filters:
Sweepstakes:
Geog 316 Fall 2006 SFSU Dr. B. Holzman
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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
Corridor
Corridor
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Filter
Filter
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
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU
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Disharmonic distribution
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
Patterns of Distribution
I. Species Niche Ecological Tolerance: Eurytopic vs StenotopicII. Distribution Patterns
Continuous/Disjunct DistributionsCosmopolitan CircumborealEvolutionary Relicts/ Climatic Relicts Disharmonic distribution (islands)
III. Endemism Neoendemics (newer distribution)Paleoendemics (ancient species)
IV. DispersalDispersal methodsOvercoming Dispersal Barriers Corridors/Filters/Sweepstakes Disharmonic distribution (islands)
Geog 316 Fall 2006 SFSU Dr. B. Holzman
For the exclusive use of students enrolled in Geog 316 at SFSU