Biology 2485B Lecture 20: Species Extinction
17 Sep 2018
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Spe(cid:272)iatio(cid:374) is o(cid:374)ly o(cid:374)e pa(cid:396)t of the e(cid:395)uatio(cid:374) that (cid:272)o(cid:374)t(cid:396)i(cid:271)utes to ea(cid:396)th(cid:859)s spe(cid:272)ies di(cid:448)e(cid:396)sity. Extinction: the disappearance of a species from earth, extinction is irreversible: once a species is lost, it is lost forever, but is currently occurring at accelerated rates as a result of human activities. Extirpation: the disappearance of a species from one part of its normal range. Population dynamics: population growth rate = births + immigration - deaths - emigration, the balance of these processes determines whether the population grows, stays the same, or declines. Major current threats to biodiversity decrease births and increase deaths. Invasive species: habitat alteration (loss, fragmentation, degradation, pollution, overharvesting, climate change. Other reasons why a population might not rebound when its size is pushed too low: random demographic events (e. g. , skew in sex ratio, genetic effects (loss of genetic variation and inbreeding) **these can also set up positive feedback loops that reduce population size further.
