Conservation Biology IB 451Ch 26: Biodiversity, Extinction + ConservationObjectivesComponents of BiodiversityExtinction is forever…Deterministic causes of extinctions: the ‘evil quintet’Conservation planning: Approach 1Focus on rare, endangered species. How is ‘rarity’ defined?Difference in vulnerability and conservation plans:Small populations at > risk to extinction via chance events, e.g.Slide 11Slide 12Criteria for long-term survival:How small is small?How big a preserve is necessary to ensure MVP?ICA 2 What’s main ‘take-home’ message?Slide 17ICA 3 What’s main ‘take-home’ message?Population Bottleneck: period of small pop. size.Populations undergoing a population bottleneck experience founder events and genetic drift,. Each causes a loss in genetic variation.Slide 21Loss of genetic variability has both qualitative & quantitative aspectsBottlenecks usually have a greater impact on loss of rare alleles than loss of genetic variance = heterozygositySlide 24Slide 25Two conclusions:Slide 27Slide 28Slide 29Slide 30Changes following the reduction in sizeSlide 32Conclusions:Slide 34ICA 6 Extinction vortex of small populations due to positive feedback loops.Slide 36Slide 37Slide 38Slide 39Population bottleneck. Partial rescue by immigration from source population.Conservation Biology IB 451-Spring 2011-Alternate yearsCh 26: Biodiversity, Extinction + ConservationObjectives•Types of biodiversity•Causes of extinction•Conservation of single species• population bottleneck + genetic diversity• small populations + inbreeding depression• documentation of loss of alleles/heterozygosity• method of restoring allelic diversity + increasing population sizeComponents of Biodiversity•Ecological diversity•Genetic diversity •Geographic diversityExtinction is forever…•Background = natural rate (1 sp. / year)•Mass extinction (up to 95% of all species) •Anthropogenic (1 sp. / day!)Deterministic causes of extinctions:the ‘evil quintet’1a habitat destruction via fragmentation (67% of cases)1b climate change2 overkill3 chains of extinction4 introduced species5 emerging diseasesConservation planning: Approach 1•Focus on ecological requirements and area needed by individual, often ‘charismatic’ species.Focus on rare, endangered species. How is ‘rarity’ defined?classicrare sp.Difference in vulnerability andconservation plans:• Small species:• small range size• human population densities-->• must protect threatened habitat• Large species:• intrinsic qualities (long development, low reproduction, low pop size -->• concentrate on increasing lx + mxSmall populations at > risk to extinction via chance events, e.g. • Demographic stochasticity• Genetic stochasticity• Environmental stochasticity and natural catastrophesAlsoAllee effect (e.g. problem finding mates)Stochastic population processes produce a probability distribution of population size.ICA 1 Probability of stochastic extinction XXXXX over time (t), but decreases as a function of XXXXXXXXX.Criteria for long-term survival:•Have Minimum Viable Population (MVP) = smallest population that can sustain itself in face of environmental variation---> avoid stochastic extinction•have wide distribution so that local catastrophe doesn’t wipe out entire population•have some population subdivision to prevent spread of diseaseHow small is small? •50/500 estimate•50 short-term: keep inbreeding low•500 long-term: allows evolution to occur without genetic drift•Effective population size = 11% of actual population sizeHow big a preserve is necessary to ensure MVP?ICA 2 What’s main ‘take-home’ message?>100<15Years50101000% pop. persistingPopulation Viability Analysis (PVA): Put demographic info into model with stochasticity added --> Predict probability of extinction within 100-1000 years Useful only if well-studied speciesICA 3 What’s main ‘take-home’ message?Years0 1000Cumulativeextinctionprobability.01%.1%1%10%100%2500 km2 No = 3000 No = 6050 km2Population Bottleneck: period of small pop. size.…subject to genetic stochasticityPopulations undergoing a population bottleneck experience founder events and genetic drift,. Each causes a loss in genetic variation.Allelebecomesfixed = novariation.+ genetic driftSmaller populations have less minisatellite variation; it has been lost by genetic drift.Loss of genetic variability has both qualitative & quantitative aspectsQualitatively, specific alleles will either be lost or retainedQuantitatively, genetic variance (or heterozygosity) will be lostBottlenecks usually have a greater impact on loss of rare alleles than loss of genetic variance = heterozygosityOriginal number of alleles = 4allele freq. = p1 = .70 p2 = p3 = p4 =.10 N = 2 (two individuals)E = # alleles retainedE = 4 - (1- .10) = .6561 (1- .10) = .6561 (1- .10) = .6561 (1- .70) = .0081- little influence-- large influence-2x#ind.E = 4 - (.0081 + .6561 + .6561 + .6561) = 2.02 alleles left of original 4Loss of alleles:ICA 4 Table 1 What affects AVERAGE # OF 4 ALLELES RETAINED?# INDIVIDUALSIN SAMPLE (N) P1=.70, P1=.94, P2=P3=P4=.10 P2=P3=P4=.02 1 1.48 1.12 2 2.20 1.23 6 3.15 1.64 10 3.63 2.00 50 3.99 3.60 >>50 4.00 4.00Two conclusions:1. More alleles are lost in populations with small numbers of individuals.2. Alleles with a low frequency in the original population tend to be lost much more easily in the small population than alleles with high frequencies.In the short run, the loss of rare alleles is probably not very important, especially in benign environments.In the long run, though, such alleles might be crucial; in an evolutionary sense.The drift-mutation balance preserves more genetic variation in large than small populations.Inbreeding decreases the frequency ofheterozygotes in a population. Allows expression of deleterious recessive alleles.ICA 5 Table 2 Size of founding pop. # % original percentagefounders heterozygosity lost retained 1 50%