Ronald J. Brooks

The case for a cause‐effect linkage between environmental contamination and development in eggs of the common snapping turtle (Chelydra s.serpentina) from Ontario, Canada

Concentrations of polychlorinated biphenyls (PCBs), dibenzo-p-dioxins, and dibenzofurans, organochlorine pesticides, and their metabolites were measured in eggs of the common snapping turtle (Chelydra s.serpentina) collected from four wetlands on the shorelines of Lakes Ontario, and Erie, and one control location in central Ontario, Canada. Snapping turtle eggs from these sites were also artificially incubated to determine hatching success, and incidence of deformities in embryo and hatchling turtles. The hypothesis that elevated incidences of egg death and/or deformities of hatchling turtles would occur in populations with high concentrations of organochlorine contaminants in eggs was tested. The results were elevated using epidemiological criteria. Unhatched eggs and deformities occurred at significantly higher rates in eggs from Lake Ontario wetlands. Two of three sites from Lake Ontario had substantially higher levels of PCBs, dioxins, and furans compared to eggs from Lake Erie and the control site. It could not be shown that contamination of eggs preceded the occurrence of poor development of eggs, although excellent hatching success and low numbers of deformities in eggs from the control site were considered representative of development in healthy eggs. The statistical association between contaminant levels in eggs and poor development of these eggs supported the hypothesis that eggs from sites with the greatest contamination had the highest rates of abnormalities. PCBs were the most strongly associated chemicals, although possible effects due to the presence of other chemicals in eggs was a confounding factor. The deformities and rates of unhatched eggs were similar to those occurring in other vertebrates collected from highly contaminated areas of the Great Lakes. There were several chemicals present in the eggs that can cause similar reproductive effects in other species; therefore a specific chemical effect was not identified. Results were coherent with known statistical and biological information. Theoretical and factual evidence of PCB contamination in wild-caught snapping turtles supported and hypothesis. However, lack of controlled studies of reproductive effects of polychlorinated hydrocarbons upon this species hindered the agreement of all factual and theoretical evidence with the hypothesis.

Social Behavior of Microtus pennsylvanicus in Relation to Seasonal Changes in Demography

A combined mark-recapture trapping and radiotelemetry study was carried out on a free-ranging population of meadow voles ( Microtus pennsylvanicus ) during summer, fall, and winter. Social relationships of pairs of neighboring voles were determined by examining their spatial and temporal use of areas of overlap. Relationships between social behavior and seasonal changes in population demography were investigated. During summer, reproductively active (RA) males had larger activity areas than RA females, and their areas overlapped substantially with those of both RA males and RA females. RA females had little or no overlap with other RA females. Neither RA males nor RA females used the overlap area with neighbors differently from random expectation. There was little contact between RA voles except when females were in estrus. Then, RA males approached the estrous female and were aggressive towards other RA males. Nonreproductive (NR) voles in summer and fall were more tolerant socially than were RA voles. In winter, activity areas of NR voles overlapped extensively, and these voles shared nests with each other. The composition of the population changed from predominantly RA voles in summer to entirely NR voles in winter.

Nest-site selection and offspring sex ratio in painted turtles, Chrysemys picta

We studied the influence of nest-site selection on nest temperature and clutch sex ratio in a northern population of painted turtles (Chrysemys picta). Comparison of characteristics of pairs of nests of individual females, within and between years, provided no evidence that these females followed a simple pattern in choosing nest sites and no indication that they influenced sex ratio by choosing sites with specific characteristics. Microhabitat features of nests were compared to the same characteristics of randomly chosen sites in the nesting area and in contrast to randomly chosen sites, nests were significantly warmer and more likely to occur on slopes. Sex ratios produced in nests were not correlated with any measured nest characteristic except temperature, and nest temperatures were more dependent on yearly variations in climate than on variations in site characteristics. Nest-temperature distributions were unimodal, suggesting that fe- males selected nest sites to maximize the probability that eggs would complete development, rather than to influence offspring sex ratio.

LONG‐TERM DYNAMICS OF SMALL‐MAMMAL POPULATIONS IN ONTARIO

We analyzed 43 yr of live-trapping data for eight species of small mammals in Algonquin Provincial Park, Ontario. Our primary objective was to test whether complex nonlinear models are necessary to describe dynamics of the Algonquin rodent populations. Variation in abundance among species was related to mean abundance by a simple power function with an exponent of 1.77, implying that population variability did not increase with mean density as much as one might expect for strictly statistical reasons. Time-series analyses of annual population densities indicated no significant autocorrelation functions for five species. Southern red-backed voles, red squirrels, and flying squirrels had significant autocorrelations, but only flying squirrels had an autocorrelation function suggestive of cyclic population dynamics. Per capita rates of population growth were density-dependent in all eight species, although in most cases there was substantial deviation around the fitted regression lines. Response surface models with one- and two-year lags significantly improved the statistical fit to data for three species, but only one of these response surface models was sustainable in the face of realistic stochastic variation in per capita growth. These results suggest that simple logistic models are adequate for predicting the long-term dynamics of the Algonquin small-mammal assemblage. All eight species showed evidence of synchronized population fluctuations over time, suggesting trophic linkages due to shared food resources, shared predators, or both.

DENSITY DEPENDENCE, PREY DEPENDENCE, AND POPULATION DYNAMICS OF MARTENS IN ONTARIO

Ecological factors influencing demographic parameters of mammalian carnivores are poorly understood, due to the difficulty of simultaneously measuring predator and prey populations over an extended period. We used cohort analysis based on age-specific harvest data to estimate population densities over 20 yr for martens (Martes americana). Marten abundance increased threefold over the study period, probably due to relaxation in harvest intensity at the beginning of the study interval. Changes in rates of population growth by martens were positively correlated with population densities of three species of small mammals recorded over the same time span: deer mice (Peromyscus maniculatus), red squirrels (Tamiasciuris hudsonicus), and flying squirrels (Glaucomys sabrinus). We found no evidence of short-term cycles in marten abundance, nor were there significant cross-correlations at lags greater than 1 with prey population densities. Martens also showed evidence of density-dependent population growth. Such density dependence beyond the demographic effect of variation in prey density was possibly due to agonistic interactions among territory holders. Such mixtures of prey dependence and density dependence often have a stabilizing influence in theoretical models, which could contribute to the observed stability of deer mouse, red squirrel, and marten populations in Algonquin Park. Harvest intensity was negatively related to yearly variation in marten population growth. Mortality due to trapping averaged 37.9% over two decades, with no detectable relationship to changes in marten population density. Hence, harvesting acted as a stochastic external variable that was additive to density-dependent and prey-dependent effects.

Chorus participation by male bullfrogs, Rana catesbeiana: a test of the energetic constraint hypothesis

Chorus tenure is the number of nights that a male anuran spends attending choruses, and dominant tenure is the number of nights that a male adopts a dominant (i.e. territorial) mating tactic. While male bullfrogs that have longer tenure (chorus tenure and dominant tenure) acquire more mates, tenure is believed to be energetically costly. During the summer of 1998, we tested the hypothesis that tenure of bullfrogs is energy constrained, by conducting a feeding experiment to manipulate energetic condition, and by measuring each males body condition on every night of his chorus tenure. The energetic constraint hypothesis did not adequately predict variation in male chorus tenure. However, male bullfrogs with longer dominant tenures, other things being equal, were in better initial condition, poorer final condition and lost condition more slowly than males with shorter dominant tenures. Feeding had no significant effect on either chorus tenure or dominant tenure. We found evidence that direct selection through endurance rivalry favoured traits in male bullfrogs that increased tenure.

Factors affecting incidence of infanticide and discrimination of related and unrelated neonates in male Mus musculus

Infanticide by males was examined in two strains (C57B1 and DBA) of the house mouse (Mus musculus). Males that had contact with a female within the previous 2-3 weeks rarely committed infanticide when introduced to the home cage of a female and her 1-day-old neonates, even when the female and neonates were of a different strain and from a different colony. In contrast, 90% of C57B1 males that had no contact with a female for more than 7 weeks killed pups when placed in the females home cage, and 60% killed when a 1-day-old pup was introduced to the males home cage. No difference in levels of infanticide occurred when grouped males were compared to isolated males. These results indicate that infanticide is not dependent upon recognition of the pups or the female, but depends on the males previous exposure to females. Infanticidal behavior is not directly determined by genetic relationship, but the factors that inhibit this behavior reduce the probability that a male will kill his own offspring.

Growth Rate, Reproductive Output, and Temperature Selection of Snapping Turtles in Habitats of Different Productivities

We compared temperature selection, growth and reproductive output between two popu- lations, and movement and home range size among three populations of the common snapping turtle (Chelydra serpentina serpentina) occupying habitats with different productivities in Ontario, Canada. We examined the hypothesis that primary productivity constrains growth, reproductive effort, and thermal and home range behavior. We predicted that individuals in a habitat with high productivity would grow faster, produce larger clutches of eggs, select warmer temperatures, and maintain smaller home ranges than individuals in a less productive habitat. As expected, turtles in the more productive habitat grew more rapidly and had a higher reproductive output than those in the less productive habitat. Turtles maintained higher body temperatures at the more productive site, but this may have been because ambient temperatures were higher at the productive site rather than because turtles were selecting higher tem- peratures. Size of home range and distances moved did not differ among study populations, which suggests that productivity was not a good proximate measure of home range behavior. Differences among sites in ambient temperature, type and distribution of prey, and turtle density made it difficult to separate the effect of each factor on growth and reproduction. Future research should measure variation among indi- viduals in energy flow, particularly to improve our understanding of variation in home range behavior.

Infanticide in the meadow vole, Microtus pennsylvanicus: significance in relation to social system and population cycling.

The relationship between social experience and readiness to commit infanticide was investigated in male meadow voles, Microtus pennsylvanicus . Shortly after a female gave birth, either the male (stud) that had sired the litter, a strange male that had had recent contact with a sexually mature female, or a strange male that had not had recent contact with a sexually mature female was placed in her cage for 24 hr. Tendency to commit infanticide was least in stud males, greatest in strange males that had no recent contact with sexually mature females, and intermediate in strange males that had recent contact with sexually mature females. Length of gestation in females impregnated by strange males was about 1.5 days longer when lactating than when not lactating. There was no difference between length of gestation of lactating females impregnated by stud males and those impregnated by strange males. Infanticide apears to be a reproductive tactic of male meadow voles, and, in conjunction with pregnancy failure in females, may have a significant influence on population regulation in this species. Dispersal may affect population cycles through the occurrence of infanticide and pregnancy failure when strange individuals immigrate into resident populations.

Habitat selection by Blanding's turtles (Emydoidea blandingii) in a relatively pristine landscape

Abstract: Identifying habitats in which a species is likely to be found is extremely important for understanding the life history and general ecology of the species. Studies of habitat selection by species at risk provide information for management and recovery programs on critical habitat and are essential for conservation programs to be effective. Many studies on species at risk are conducted in highly altered or degraded habitats because few areas have not experienced human impacts. We investigated habitat selection by Blandings turtles (Emydoidea blandingii) in a large protected area, Algonquin Park. Specifically, we evaluated macrohabitat selection at 2 spatial scales (home range and individual location) and microhabitat selection at one scale. Macrohabitat selection was significant at the home range scale but not at the scale of individual location, and no shift in habitat selection was detected among different seasons. Habitat ranks were ambiguous because all wetland types were preferred over lotic and upland habitats. The microhabitat selection data showed no preference for habitat features or shifts among different seasons. These data combined with those from other studies suggest that large study sites in relatively pristine areas may include a large amount of suitable high-quality habitats such that habitat selection at a fine scale may not be detected or multiple habitat types may provide the resources necessary to support populations. Nomenclature: Ernst & Lovich, 2009.