Section 8 Genetically Viable Populations Habitat loss = loss of living space for threatened and endangered species. mammals56% birds53% reptiles62% amphibians64% fish56% gymnosperms32% angiosperms9%

Currently, about 2,000 endangered vertebrate species require captive breeding. Space exists for only about 800 species. Important question Important question: “How large must populations be to be genetically viable?” We must consider what is the minimum size required to maintain a population that suffers no reduction in reproductive fitness or evolutionary potential over thousands of years!

For a particular population or species: Is the population size large enough to avoid loss of reproductive fitness? Does the species have enough genetic diversity to evolve in response to environmental changes?

We do not know precisely how large populations must be to avoid meaningful inbreeding depression in the long-term. However, the required size clearly is much larger than an effective size of 50. Disturbingly, about 1/2 of all captive populations of threatened mammals have N of less than 50!

Genetic Goals in the Management of Wild Populations Only a few examples of management plans for endangered species in wild where genetic objectives are defined. Genetic objectives for the Golden Lion Tamarin is to retain 98% of the genetic diversity for 100 years.

Genetic Goals in the Management of Wild Populations To obtain the required population size: H t /H 0 = e -t/2Ne Substituting H t /H 0 = 0.98 and t = 100/6 = 16.7: 0.98 = e -16.7/2Ne = e /Ne N e = -8.33/ln 0.98 = 412

Genetic Goals in the Management of Wild Populations Currently: 630 individuals in the wild 360 individuals in the wild from reintroductions 500 individuals in captivity.

N e /N ratio must exceed 0.31 to attain the genetic goals based on all animals, or 0.5 for wild animals. Since this is unlikely, the genetic goals are NOT being achieved. Lack of available habitat to allow expansion of the population is the primary obstacle to reaching these goals.

Recovery Targets for Population Sizes Used to de-list Species. Recovery programs often identify a target population size, the size at which the species would be removed from the endangered list. While most target sizes are in the thousands, they are generally less than genetic arguments would require based on a N e /N ratio of about 0.1.

Peregrin Falcon = 900 to delist California Condor only 450 to delist Number of Ozark big-eared bats to delist = ????

Genetic goals in management of captive populations A Compromise Much fewer captive resources available than required to maintain all species deserving captive breeding, especially considering the recommended N e =500 per species. Zoos house about 540,000 mammals, birds, reptiles, and amphibians. About half the species are suitable for propogating endangered animals.

About 2,000 vertebrate species require captive breeding to save them from extinction. To maintain each of these at N e = 500 (assuming N e /N = 0.3 in captivity) would require 3,300,000 animal spaces, about 12 times the space currently available. At an average census size of 500, only 540 species can be accommodated. Currently only 15% of mammal spaces in zoos house threatened species.

The current compromise is to manage endangered species in captivity to conserve 90% of the wild populations genetic diversity for 100 years. The 100 year time frame was chosen because it is estimated that wild habitat may become available following the predicted human population decline in years. This requires different population sizes for species with different generation lengths.

H t /H 0 ≈ e -t/2Ne taking natural logarithm, substituting 0.9 for H t /H 0, 100/L for t (where L is generation length in years), and rearranging we obtain: N e = 475/L Consequently, the required size is inversely proportional to the generation length for the species in question.

N e required to maintain 90% or original heterozygosity for 100 years is: 475 for a species with 1 generation/year 18 for Carribean Falmingos with 1 generation every 26 years. 1,759 for white-footed mice with a generation length of 14 weeks.

Maintaining 90% of genetic diversity for 100 years is a reasonable goal. However, many species are being maintained with lesser goals (and smaller sizes) due to shortage of resources. The cost of this compromise is increased in inbreeding & reduced reproductive fitness: F = 1 - (H t /H o )

Accepted 10% loss of heterozygosity corresponds to a 10% increase in F with concomitant inbreeding depression. After 100 years, individuals will be related to each other to a degree somewhere between that of F = first cousins (F = ) and half-siblings F = (F = 0.125). This will reduce juvenile survival on average by about 15% and total fitness by about 25%, in captivity.

These values ignore the bottleneck associated with founding populations and assumes that population numbers can immediately rise to the desired level. Captive populations typically have few founders and grow slowly to their final size. These factors lead to greater loss of genetic diversity early in captive breeding programs than predicted.

Consequently, effective population sizes required to retain 90% of genetic diversity for 100 years are typically greater than predicted!!!!!!