100 number of species la selva costa rica 50 orono

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Unformatted text preview: 0 8 64 512 4096 Number of individuals/species M3.14 BIO 3115 Université d’Ottawa / University of Ottawa M3 2009-2010.7 BIO 3115 Conservation Biology Kinds of rarity I: Geographical distributions Some species are considered rare because they are found in only one or a few geographical areas E.g. the Komodo dragon & Mountain gorilla. . M3.15 BIO 3115 Université d’Ottawa / University of Ottawa Kinds of rarity II: Habitat specificity Some species are considered rare because while they may have a wide geographic range, within this range, they are found only in specific habitats E.g. Kirtland’s warbler requires 10-15 yr old Jack Pine forests for breeding M3.16 BIO 3115 Université d’Ottawa / University of Ottawa M3 2009-2010.8 BIO 3115 Conservation Biology Kinds of rarity III: Population size Some species are considered rare because where they occur, local population sizes are small E.g. Grizzly bear; 95% chance of persisting 100 yrs requires N = 70- 90 bears. 1922 1992 M3.17 BIO 3115 Université d’Ottawa / University of Ottawa Forms of rarity - framework for classifying rarity Rarity per se does not necessarily mean that a sp is in danger of extinction (some spp are naturally rare!) For assessment of vulnerability, changes in population size are more important than absolute densities Rabinowitz (1981) categorized species status on the basis of 3 characteristics: 1] size of geographic range (large vs. small) 2] Habitat specificity (broad vs. narrow) 3] Local population size (large vs small) All possible combinations of these characteristics yield different forms of rarity M3.18 BIO 3115 Université d’Ottawa / University of Ottawa M3 2009-2010.9 BIO 3115 Conservation Biology Rarity and extinction risk: size of geographical range Species that are found in only a small number of geographical areas are at higher risk because if the populations in these few areas are lost, the entire species is lost. Extinction risk Species 1 Species 2 Species 1 Species 2 M3.19 BIO 3115 Unive...
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