Dale R. McCullough

Population Viability Analysis

As human populations and the resources required to support societies continue to grow, an increasing number of plant and animal species around the world are facing extinction. Given limited time, space, and money, how do we decide which management actions will be most effective to avert extinctions? In this book, many of the worlds leading conservation and population biologists evaluate what has become a key tool in estimating extinction risk and evaluating potential recovery strategies - population viability analysis, or PVA. PVA integrates data on the life history, demography, and genetics of a species with information on environmental variability, using computer models ranging from simple measures of population growth rate to complex spatial simulations, to predict whether a given population will remain viable (i.e., not go extinct) under various management options. A synthetic and objective overview of the latest theoretical and methodological advances, Population Viability Analysis will be crucial reading for conservationists, land managers, and policy makers.

The George Reserve deer herd : population ecology of a K-selected species

A reassessment of the studies done on this deer herd over the years and their implications for state wildlife management agencies.

Deer-Car Accidents in Southern Michigan

Collisions of cars with white-tailed deer (Odocoileus virginianus) were studied in southern Michigan in 1966 and 1967. Most of the 2,566 accidents studied occurred at dawn, dusk, or after dark with peaks at sunrise and 2 hours after sunset. Accidents were highest on weekends when evening traffic was greatest. A low seasonal peak in collisions occurred in May and a high one in November. Sex ratio of the annual kill was predominately female, but it shifted in favor of males during seasonal peaks. Causes of the peaks seemed to be primarily rutting activities, with hunter disturbance and food of lesser importance. Accidents were related to habitat type approximately according to the prevalence of the type. Accidents were most common at speeds of 80-95 km/h (50-59 mph), and the deer was killed in 92 percent of the accidents. Human injuries occurred in less than 4 percent, and most resulted from secondary collisions.

Bottlenecks, drift and differentiation: the population structure and demographic history of sika deer (Cervus nippon) in the Japanese archipelago

We assessed genetic differentiation and diversity in 14 populations of sika deer (Cervus nippon) from Japan and four populations of sika deer introduced to the UK, using nine microsatellite loci. We observed extreme levels of differentiation and significant differences in diversity between populations. Our results do not support morphological subspecies designations, but are consistent with previous mitochondrial DNA analyses which suggest the existence of two genetically distinct lineages of sika deer in Japan. The source of sika introduced to the UK was identified as Kyushu. The underlying structure of Japanese populations probably derives from drift in separate glacial refugia and male dispersal limited by distance. This structure has been perturbed by bottlenecks and habitat fragmentation, resulting from human activity from the mid‐nineteenth century. Most current genetic differentiation and differences in diversity among populations probably result from recent drift. Coalescent model analysis suggests sika on each of the main Japanese islands have experienced different recent population histories. Hokkaido, which has large areas of continuous habitat, has maintained high levels of gene flow. In Honshu the population is highly fragmented and is likely to have been evolving by drift alone. In Kyushu there has been a balance between gene flow and drift but all the populations have experienced high levels of drift. Habitat fragment size was not significantly associated with genetic diversity in populations but there was a significant correlation between habitat fragment size and effective population size.

Spatially Structured Populations and Harvest Theory

Harvest theory is examined with reference to spatially-structured population systems. Harvest from continuously-distributed populations, which usually are based on regulation of size of kill (numerical control), can be achieved by spatial controls through a mosaic of hunted and unhunted areas. Spatial controls can achieve high yields and avoid the hazards of overharvest that are common with harvest quotas without detailed population data (requiring only an estimate or index of harvest). Harvesting of metapopulations is examined and found to hold little prospect because of negative effects on dispersal required for recolonization of patches following local extinction.

Density Dependence and Life-History Strategies of Ungulates

Due to their large sizes and long life spans, ungulates typically exist in populations close to environmental carrying capacity (CC), and this has had a strong influence on evolution of life-history traits. I review models describing the relationship of ungulate populations to CC. The shape of the functional relationship of density dependence (DD) on population size (N) determines the response of N relative to CC and the tendency of N to come to equilibrium at CC. Environmental, and to a lesser extent demographic, stochasticity determine the realized relationship of N to CC in nature. It is difficult to distinguish DD signals from noise in environments with high stochasticity or with populations at or near CC. Life-history strategies of ungulates evolved in the context of DD and CC. Sexual selection has resulted in asymmetry of reproductive success between sexes and consequent evolution of dimorphism in body size with males being larger than females. Because males have larger bodies, greater absolute nutrient and energy costs, and higher rates of mortality than females, their reproductive fitness strategies tend to skew the population sex ratio towards females. Females are less costly to produce and maintain, so increased skew in the sex ratio of the population should, in theory, result in greater N (higher CC) relative to a given resource base. Sexual selection should lead to increasingly skewed sexual dimorphism and sex ratio up to some constraint set by the males physical ability to sequester females or physiological limits to impregnate females. This suite of life-history traits in ungulates has led to resource partitioning between sexes and sexual segregation outside of the rut in most species. Female-female competition also complicates the relative value of sex of offspring to individual females, which varies with female age, size, and social position.

Territoriality and breeding status of coyotes relative to sheep predation

Coyote (Cauis latrans) depredation is a chronic problem for sheep producers in the western United States. Due to increasingly localized control efforts, behavior of individual coyotes in sheep-ranching environments is becoming a more important consideration. We radiotracked 14 coyotes on a year-round sheep-ranching facility in north-coastal California during September 1993-December 1995. Breeding coyote pairs used mutually exclusive territories (maximum overlap between 90% adaptive kernel home ranges = 4%). Nonbreeding coyotes were transient or varied in their degree of fidelity to putative natal territories but generally avoided cores of nonnatal territories. Breeding coyotes whose territories contained sheep were the principal predators of sheep. In the 1994 lambing period (1 Jan-31 May). radiotelemetry indicated that 1 breeding male was responsible for 71% of 65 kills. In the 1995 lambing period, 4 breeding pairs were strongly implicated in 92% of 48 kills and were suspected of 85% of 26 additional kills; nonbreeders were not associated with sheep depredation. Depredation was reduced only when territorial breeders known to kill sheep were removed. These results suggest the need for management to target breeding adults in the immediate vicinity of depredation. Efforts to remove individuals > 1 territory-width away from problem sites are unlikely to reduce depredation and may exacerbate the problem by creating vacancies for new breeders that might kill sheep.

Resource partitioning between sexes in white-tailed deer

We tested resource partitioning between sexes of white-tailed deer (Odocoileus virginianus) by analyzing spatial and temporal distribution of each sex on the George Reserve, Michigan. Mean overlap of sexes by season was approximately 56%. Overlap was greatest during severe weather in January and least during fawning in May. Areas of concentration of each sex shifted between seasons. Females showed greater dispersion than males. There was differential use of habitats by the sexes at some seasons. Differential use of habitats was greatest when spatial overlap of sexes was highest, and vice versa. Differential use of space and habitats, in conjunction with differences in diets and diet quality, help explain the apparent lack of competition between sexes. J. WILDL. MANAGE. 53(2):277-283 An unexpected outcome of manipulations of the enclosed white-tailed deer population on the George Reserve, Michigan, was that recruitment rate was negatively correlated with number of females, but was independent of the number of males (McCullough 1979). Social factors could be ruled out because recruitment responded differently at the same population size before and after an overshoot of carrying capacity following the initial introduction (McCullough 1984:216-217), and this result was repeated in a recent overshoot experiment (D. R. McCullough, unpubl. data). Given that resources were the limiting variable, one would have expected that density per se, irrespective of sex, would be important because resources are depleted by the feeding of both sexes. Apparently, resource partitioning between sexes must exist on the George Reserve if competition for resources among females is more direct than competition between females and males. Studies of sexual segregation in ungulates have emphasized the hypothesis of reduction of competition for resources first put forward by Darwin (1871) and elaborated by Selander (1966, 1972) for birds. Spatial segregation of the sexes in the nonbreeding season is well known in ungulates (Darling 1937, Dasmann and Taber 1956, Welles and Welles 1961). Also, differences in diets between sexes have been reported by Takatsuki (1980) in sika deer (Cervus nippon), and Shank (1982) in bighorn sheep (Ovis canadensis). Jackes (1973), Watson and Staines (1978), and Bowyer (1984) reported that females occupied better habitat than males, and Staines and Crisp (1978) and Staines et al. (1982) reported that females selected more nutritious for-

Effect of coyote removal on sheep depredation in northern California

We used 13 years of historical data to investigate effects of coyote (Canis latrans) removal on depredation of domestic sheep. The 2,168-ha study area maintained >1,000 breeding ewes that produced lambs yearly. Records from 1981 through 1994, which included numbers of sheep, numbers of sheep known killed by coyotes, known numbers of coyotes removed, and annual numbers of trapper hours were summarized and analyzed on a yearly, seasonal, and monthly basis. We used regression analysis and found that annual, seasonal, or monthly depredation losses were not correlated with number of coyotes removed. Both annual number of lambs killed and number of coyotes removed were positively correlated with number of trapper hours. We used a cross-correlation analysis to detect any relation between coyote removal and subsequent depredation losses at all monthly intervals from 0 to 24 months. We found a trend of low negative correlation between depredation losses and number of coyotes removed for lags of 2-12 months, suggesting some reduction of sheep killing due to control efforts. Low correlations within years may be due to inconsistent removal of depredating coyotes while removing primarily young, nondepredating coyotes. Lack of correlation between years may have occurred because past control efforts have not had a lasting reduction on coyote density due to immigration, the compensatory nature of control efforts on coyote mortality, reproductive compensation in the resident coyote population, or all 3 factors.

The effectiveness of selective removal of breeding coyotes in reducing sheep predation

We evaluated the effect on sheep losses of selectively removing breeding coyotes (Canis latrans) from territories experiencing depredations. Breeding pairs of coyotes were the primary predators of sheep, and they killed sheep only within or on the periphery of their territories. Removal of either or both members of a breeding pair reduced or eliminated predation in that territory during the subsequent 3-month period. Killing of sheep by coyotes d sooner in territories that overlapped lambing pastures than in those that did not. For territories with access to lambs, the average time interval until killing of lambs resumed (43 days) approximated the time for a replacement pair of coyotes to become established. Removals of breeding coyotes during the nonlambing season did not reduce losses during the following lambing season. Although <33% as many coyotes were removed per unit time during selective control as during nonselective control, lambing-season lamb losses were lowest during the selective removal period. During the nonlambing period (when predation on sheep was low) sheep losses were similar under selective, nonselective, and no control. These results suggest that selective targeting of breeding coyotes, which is more socially acceptable than nonselective population reduction, also can be more effective in reducing sheep losses.