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Effective population size, a central concept in conservation biology, is now routinely estimated from genetic surveys and can also be theoretically predicted from demographic, life-history, and mating-system data. By evaluating the consistency of theoretical predictions with empirically estimated effective size, insights can be gained regarding life-history characteristics and the relative impact of different life-history traits on genetic drift. These insights can be used to design and inform management strategies aimed at increasing effective population size. We demonstrated this approach by addressing the conservation of a reintroduced population of Asiatic wild ass (Equus hemionus). We estimated the variance effective size (N ev ) from genetic data (N ev =24.3) and formulated predictions for the impacts on N ev of demography, polygyny, female variance in lifetime reproductive success (RS), and heritability of female RS. By contrasting the genetic estimation with theoretical predictions, we found that polygyny was the strongest factor affecting genetic drift because only when accounting for polygyny were predictions consistent with the genetically measured N ev . The comparison of effective-size estimation and predictions indicated that 10.6% of the males mated per generation when heritability of female RS was unaccounted for (polygyny responsible for 81% decrease in N ev ) and 19.5% mated when female RS was accounted for (polygyny responsible for 67% decrease in N ev ). Heritability of female RS also affected N ev ; hf2=0.91 (heritability responsible for 41% decrease in N ev ). The low effective size is of concern, and we suggest that management actions focus on factors identified as strongly affecting Nev, namely, increasing the availability of artificial water sources to increase number of dominant males contributing to the gene pool. This approach, evaluating life-history hypotheses in light of their impact on effective population size, and contrasting predictions with genetic measurements, is a general, applicable strategy that can be used to inform conservation practice., (© 2017 Society for Conservation Biology.)

Theory proposes that increased environmental stochasticity negatively impacts population viability. Thus, in addition to the directional changes predicted for weather parameters under global climate change (GCC), the increase in variance of these parameters may also have a negative effect on biodiversity. As a case study, we assessed the impact of interannual variance in precipitation on the viability of an Asiatic wild ass (Equus hemionus) population reintroduced in Makhtesh Ramon Nature Reserve, Israel. We monitored the population from 1985 to 1999 to determine what environmental factors affect reproductive success. Annual precipitation during the year before conception, drought conditions during gestation, and population size determined reproductive success. We used the parameters derived from this model to assess population performance under various scenarios in a Leslie matrix type model with demographic and environmental stochasticity. Specifically, we used a change in the precipitation regime in our study area to formulate a GCC scenario and compared the simulated dynamics of the population with a no-change scenario. The coefficient of variation in population size under the global change scenario was 30% higher than under the no-change scenario. Minor die-offs (> or = 15%) following droughts increased extinction probability nearly 10-fold. Our results support the idea that an increase in environmental stochasticity due to GCC may, in itself, pose a significant threat to biodiversity.

Empirical data on behavior, such as space-use patterns, are important to the success of animal reintroductions. We studied space-use patterns in a growing population of Asiatic wild ass (   Equus hemionus) reintroduced into the Ramon erosion cirque in the Negev desert, Israel. Between 1988 and 1995 we used direct observation to determine the location and association of males and females. All adult females and dominant males were individually recognized. Home ranges of dominant males overlapped little, suggesting that in this population males are territorial. After the first release of males and females into the wild, only one territory was established, and it covered most of the 20,000 ha of the cirque. After 6 years the number of male territories increased as the number of males in the population increased, and average territory size decreased. Male territories were near permanent and ephemeral water sources, but the water sources were at the peripheries of the territories and were not centers of activity. When there was only one territorial male, female home ranges were almost entirely within the territory. As male territory size decreased, so did the spatial association of females with a single male. During the breeding season, males spent more time in close association with female groups, adopting what may temporarily appear to be a harem breeding strategy. Although demographic and environmental factors pose a greater threat to small populations, our data support the hypothesis that in small, reintroduced populations of territorial, polygynous species, effective population size (  N e   ) may be dangerously small. Our data suggest that this situation may last for several years until new males are recruited into the population. Thereafter, rapid male turnover and female use of several male territories may ameliorate this problem. We found no relationship between male turnover rate and female reproductive success. The establishment of more male territories is key to increasing N e and should be the basis for planning reserves for territorial, polygynous species.