6 - Ecological factors in population persistence

20 bio 3115 universit dottawa university of ottawa

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Unformatted text preview: f extinction risk I: current population size (N) As current population size increases, extinction risk declines (likelihood of population persistence increases) E.g. extinction rates of bird spp on the California Channel islands. Shown are % of populations of different size classes that became extinct during the study. If N<10 breeding pairs, 39% went extinct during 80 yrs; If N=10-100 pairs, 10% extinct If N>1000 pairs, no extinctions! 60 50 % extinctions 40 30 20 10 0 1 10 100 1000 10000 Population size (# pairs) M6.21 BIO 3115 Université d’Ottawa / University of Ottawa Percent of populations persisting Relationship between population size of bighorn sheep and persistence N = 101 or more 100 80 N = 51-100 60 N = 16-30 40 N = 31-50 N = 15 or less 20 0 10 20 30 40 50 Time (years) M6.22 BIO 3115 Université d’Ottawa / University of Ottawa M6.11 BIO 3115 Conservation Biology High r High V(r) High r Low V(r) Population size Population size Predictors of extinction risk II: Effect of population growth rate (r) and variability in r (V(r)) Time Time Population size Population size Low r High V(r) Low r Low V(r) Time Time Extinction risk M6.23 BIO 3115 Université d’Ottawa / University of Ottawa Estimated extinction probabilities for continent al U.S. grizzly populations Population Estimated size Extinction probability (500 yrs) Northern Divide 306 0.342 Yellowstone 236 0.392 Selkirks 25 0.823 Cabinet/Yoak 15 0.890 North Cascades 5 0.974 M6.24 BIO 3115 Université d’Ottawa / University of Ottawa M6.12 BIO 3115 Conservation Biology Predictors of extinction risk II: Effect of population growth rate (r) and variability in r (V(r)) What is the relative importance of r vs V(r)? If r is high, then a population should recover relatively fast after a population decline, thereby lowering the chances of extinction! If r is low, then any major catastrophy may wipe out the population, and, due to low r, the population cannot recover, resulting in a high risk of extincti...
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This document was uploaded on 03/11/2014 for the course BIO 3115 at University of Ottawa.

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