Lecture 10.pdf
- 2. 2 Introduction • Ecologists usually define a population as a group of individuals of a single species inhabiting a specific area. • Additional characteristics of a population include age distributions, growth rates, distribution, and abundance.
- 3. 3 Distribution Limits • Physical environment limits geographic distribution of a species. • Organisms can only compensate so much for environmental variation.
- 4. 4 Niches • Niche: Summarizes environmental factors that influence growth, survival, and reproduction of a species. • Grinnell’s definition focused on the effects of the physical environment • Elton’s definition included biotic and abiotic factors • Hutchinson defined niche as: • "living space" delineated by the entire range of environmental conditions that an organism can tolerate and by all the resources it requires for survival, growth, and reproduction.
- 5. 5 Kangaroo Distributions and Climate • Scientist found a close relationship between climate and distribution of the three largest kangaroos in Australia. • Macropus giganteus - Eastern Grey • Eastern 1/3 of continent. • Macropus fuliginosus - Western Grey • Southern and western regions. • Macropus rufus - Red • Arid / semiarid interior.
- 6. 6 Kangaroo Distributions and Climate
- 7. 7 CONT.. • Limited distributions may not be directly determined by climate. • Climate often influences species distributions : • Food production • Water supply • Habitat • Incidence of parasites, pathogens and competitors.
- 8. 8 Tiger Beetle and Cold Climates • Tiger Beetle (Cicindela longilabris) lives at higher latitudes and elevations than most other species in NA. • Schultz et. al. found metabolic rates of C. longilabris are higher and preferred temperatures lower than most other species.
- 9. 9 Tiger Beetle of Cold Climates
- 10. 10 Distributions of Plants along a Moisture-Temperature Gradient • Encelia species distributions correspond to variations in temperature and precipitation.
- 11. 11 Distributions of Barnacles along an Intertidal Exposure Gradient • Organisms living in an intertidal zone have evolved to different degrees of resistance to drying. • Barnacles show distinctive patterns of zonation within intertidal zone.
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- 13. 13 Distribution of Individuals on Small Scales • Random: Equal chance of being anywhere. • Regular: Uniformly spaced. • Exclusive use of areas. • Individuals avoid one another. • Clumped: Unequal chance of being anywhere. • Mutual attraction between individuals. • Patchy resource distribution.
- 14. 14 Distribution of Individuals on Small Scales
- 15. 15 Distributions of Individuals on Large Scales • Bird Populations Across North America • Scientist T. Root found at continental scale, bird populations showed clumped distributions in Christmas Bird Counts. • Clumped patterns occur in species with widespread distributions. • Brown found a relatively small proportion of study sites yielded most of records for each bird species in Breeding Bird Survey.
- 16. 16 By Dr Azimah Abd Rahman, PPSKH, USM
- 17. 17 Plant Abundance along Moisture Gradients • Whittaker examined distributions of woody plants along moisture gradients in several North American mountain ranges. • Documented moisture gradient from moist canyon bottoms up to the dry southwest-facing slopes. • Tree species showed a highly clumped distribution along moisture gradients, with densities decreasing substantially toward the edges of their distribution.
- 18. 18 Plant Abundance Along Moisture Gradients
- 19. 19 Organism Size and Population Density • In general, population density declines with increasing organism size. • Damuth found the population density of herbivorous mammals decreased with increased body size. • Peters and Wassenberg found aquatic invertebrates tend to have higher population densities than terrestrial invertebrates of similar size. • Mammals tend to have higher population densities than birds of similar size.
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- 21. 21 Plant Size and Population Density • Plant population density decreases with increasing plant size. • Underlying details are very different. • Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities.
- 22. 22 Commonness and Rarity • Rabinowitz devised commonness classification based on (3) factors: • Geographic Range of Species • Habitat Tolerance • Local Population Size • Populations that are least threatened by extinction, have extensive geographic ranges, broad habitat tolerances, and some large local populations.
- 23. 23 Rarity • Rarity I • Extensive Range, Broad Habitat Tolerance, Small Local Populations • Peregrine Falcon • Rarity II • Extensive Range, Large Populations, Narrow Habitat Tolerance • Passenger Pigeon
- 24. 24 Rarity • Rarity III • Restricted Range, Narrow Habitat Tolerance, Small Populations • California Condor • Arizona & California • Critically Endangered