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Geog 316 Fall 2006 SFSU Dr. B. Holzman Patterns of Distribution I. Species Niche Ecological Tolerance Eurytopic vs Stenotopic II. Distribution Patterns Continuous/Cosmopolitan Disjunct Distributions Evolutionary Relicts Climatic Relicts III. Endemism Neoendemics Paleoendemics IV. Dispersal Overcoming 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 For the exclusive use of students enrolled in Geog 316 at SFSU 1 Geog 316 Fall 2006 SFSU Dr. B. Holzman • 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. For the exclusive use of students enrolled in Geog 316 at SFSU 2 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 3 Geog 316 Fall 2006 SFSU Dr. B. Holzman Continuous Distribution The species, Bradypus variegatus, is endemic to the tropical and subtropical regions of the American continent (Grasse 1955). For the exclusive use of students enrolled in Geog 316 at SFSU 4 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 5 Geog 316 Fall 2006 SFSU Dr. B. Holzman Distribution: Cosmopolitan Distribution: Cosmopolitan Northern hawk owl Circumboreal distribution: around the northern regions. distribution of organisms possibly representing the past movements of continents For the exclusive use of students enrolled in Geog 316 at SFSU 6 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 7 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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. Magnolias Tulip trees Distributions: Disjunct Process: Evolutionary Relict For the exclusive use of students enrolled in Geog 316 at SFSU 8 Geog 316 Fall 2006 SFSU Dr. B. Holzman Disjunct Distributions: Process: Evolutionary Relict Disjunct :Relicts 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 Climate relict • Dodecatheon: glacial relict Dawn redwood: Pre glaciation For the exclusive use of students enrolled in Geog 316 at SFSU 9 Geog 316 Fall 2006 Disjunct Distribution SFSU Dr. B. Holzman Mountain gorilla Lowland gorilla 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 For the exclusive use of students enrolled in Geog 316 at SFSU 10 Geog 316 Fall 2006 SFSU Dr. B. Holzman DISJUNCT DISTRIBUTION Endemic Organisms ENDEMIC: 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 For the exclusive use of students enrolled in Geog 316 at SFSU 11 Geog 316 Fall 2006 SFSU Dr. B. Holzman Kangaroo rat For the exclusive use of students enrolled in Geog 316 at SFSU 12 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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. Limnanthes floccosa Oenothera californica Paleoendemics • Carpenteria californica, Lyonothamnus floribundus, Pinus radiata, P. torreyana, and Sequoiadendron gigantea are paleoendemics that were once more broadly distributed, but have retreated to their current ranges in response to dramatic climatic change. For the exclusive use of students enrolled in Geog 316 at SFSU 13 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 14 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 15 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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: For the exclusive use of students enrolled in Geog 316 at SFSU 16 Geog 316 Fall 2006 SFSU Dr. B. Holzman Dispersal Routes Corridors: 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 For the exclusive use of students enrolled in Geog 316 at SFSU 17 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 For the exclusive use of students enrolled in Geog 316 at SFSU 18 Geog 316 Fall 2006 SFSU Dr. B. Holzman 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 Stenotopic II. Distribution Patterns Continuous/Disjunct Distributions Cosmopolitan Circumboreal Evolutionary Relicts/ Climatic Relicts Disharmonic distribution (islands) III. Endemism Neoendemics (newer distribution) Paleoendemics (ancient species) IV. Dispersal Dispersal methods Overcoming Dispersal Barriers Corridors/Filters/Sweepstakes Disharmonic distribution (islands) For the exclusive use of students enrolled in Geog 316 at SFSU 19