Karen E. Mabry

Social Mating System and Sex-Biased Dispersal in Mammals and Birds: A Phylogenetic Analysis

The hypothesis that patterns of sex-biased dispersal are related to social mating system in mammals and birds has gained widespread acceptance over the past 30 years. However, two major complications have obscured the relationship between these two behaviors: 1) dispersal frequency and dispersal distance, which measure different aspects of the dispersal process, have often been confounded, and 2) the relationship between mating system and sex-biased dispersal in these vertebrate groups has not been examined using modern phylogenetic comparative methods. Here, we present a phylogenetic analysis of the relationship between mating system and sex-biased dispersal in mammals and birds. Results indicate that the evolution of female-biased dispersal in mammals may be more likely on monogamous branches of the phylogeny, and that females may disperse farther than males in socially monogamous mammalian species. However, we found no support for a relationship between social mating system and sex-biased dispersal in birds when the effects of phylogeny are taken into consideration. We caution that although there are larger-scale behavioral differences in mating system and sex-biased dispersal between mammals and birds, mating system and sex-biased dispersal are far from perfectly associated within these taxa.

Climate change, body size, and phenotype dependent dispersal

Gardner and colleagues [1] recently reviewed the evidence for shifts in body size as a third major response to climate change, in addition to widely recognized shifts in the ranges and phenology of species [2]. The authors conclude that, although a pattern of declining body size is commonly observed (i.e. [3]), increases in body size might also occur and more detailed studies are needed [1]. Although their review focuses on the evidence for declining body size as a third general response to climate change, we would like to add that the effect of climate on individual body size has the potential to impact one of the other major responses to climate change dramatically: species’ range shifts (Figure 1).

Effects of experimental warming on survival, phenology, and morphology of an aquatic insect (Odonata)

1. Organisms can respond to changing climatic conditions in multiple ways including changes in phenology, body size or morphology, and range shifts. Understanding how developmental temperatures affect insect life‐history timing and morphology is crucial because body size and morphology affect multiple aspects of life history, including dispersal ability, whereas phenology can shape population performance and community interactions.

Are body mass and parasite load related to social partnerships and mating in Microtus ochrogaster

Abstract Within socially monogamous species, a males reproductive success depends on his success at obtaining a social partner with which he mates, as well as gaining extra-pair matings. We investigated the impacts of body mass and parasitism on 2 measures of a males success at obtaining a social partner (number of female social associations and relative strength of a social bond to a single female) and 2 measures of reproduction (number of females with which a male sires offspring and the number of offspring sired) in natural populations of prairie voles (Microtus ochrogaster) located in Kansas and Indiana. Kansas males with greater endoparasite loads were less likely to have one social partner. Instead, they associated with multiple females although they did not sire offspring with more females than males with lower levels of endoparasitism. We did not find any relationship between endoparasite infestation and the number of females with which males associated in Indiana. There was no association between the level of endoparasites found among males in either Indiana or Kansas and the strength of a males social bond to a female. Endoparasites, at least at the infection levels detected in this study, were not related to indices of male reproductive success in Microtus populations in Kansas or Indiana. No relationship was found between body mass and indicators of social monogamy in either population. However, body mass appears to be significantly related to male reproductive success. Heavier males produced offspring with more females, particularly in the Kansas population, and sired more pups in both populations.

Effects of exurban development on trophic interactions in a desert landscape

ContextMechanisms of ecosystem change in urbanizing landscapes are poorly understood, especially in exurban areas featuring residential or commercial development set in a matrix of modified and natural vegetation. We asked how development altered trophic interactions and ecosystem processes in the matrix.ObjectivesWe examined the effect of varying degrees of exurban development (housing density) on a trophic system that included an apex mammalian predator (coyote, Canis latrans), mammalian herbivores (lagomorphs and rodents), and herbaceous plants. We tested the hypothesis that plant recruitment would be negatively affected by exurban development due either to increases in herbivores associated with increased resource availability (a bottom–up effect) or to a reduction in predators that avoid humans (a top–down effect).MethodsIn Las Cruces, New Mexico, USA, four replicate sites were located in each of three urbanization levels: high density exurban, low density exurban, and wildland dominated by Chihuahuan Desert vegetation. Seedling trays measured herbivory rates, live trapping estimated abundance of pocket mice and kangaroo rats, and remotely-triggered wildlife cameras estimated the activity of lagomorphs and coyotes.ResultsIncreased herbivory on seedlings and decreased herbaceous plant recruitment were observed in high density exurban areas. Overall rodent abundance, seed consumption rates, and activity of the lagomorph Lepus californicus did not vary with urbanization level. Activity by another lagomorph, Sylvilagus audubonii, and coyotes was highest in dense exurban areas, consistent with a bottom–up effect.ConclusionsExurban development can have important indirect effects on trophic interactions occurring in adjacent, untransformed ecosystems. Similar to earlier studies, such effects in the Chihuahuan Desert may be mediated by bottom–up processes associated with anthropogenic inputs.

Effects of Natural and Anthropogenic Change on Habitat Use and Movement of Endangered Salt Marsh Harvest Mice

The northern salt marsh harvest mouse (Reithrodontomys raviventris halicoetes) is an endangered species endemic to the San Francisco Bay Estuary. Using a conservation behavior perspective, we examined how salt marsh harvest mice cope with both natural (daily tidal fluctuations) and anthropogenic (modification of tidal regime) changes in natural tidal wetlands and human-created diked wetlands, and investigated the role of behavioral flexibility in utilizing a human-created environment in the Suisun Marsh. We used radio telemetry to determine refuge use at high tide, space use, and movement rates to investigate possible differences in movement behavior in tidal versus diked wetlands. We found that the vast majority of the time salt marsh harvest mice remain in vegetation above the water during high tides. We also found no difference in space used by mice during high tide as compared to before or after high tide in either tidal or diked wetlands. We found no detectable difference in diurnal or nocturnal movement rates in tidal wetlands. However, we did find that diurnal movement rates for mice in diked wetlands were lower than nocturnal movement rates, especially during the new moon. This change in movement behavior in a relatively novel human-created habitat indicates that behavioral flexibility may facilitate the use of human-created environments by salt marsh harvest mice.

Spatial variation in population density affects dispersal behavior in brush mice

Population density can influence all three phases of natal dispersal: departure from the place of birth, searching the landscape, and selecting a new site in which to settle. The direction of the effect of density on dispersal should be affected by the relative costs and benefits of living in an area with high population density. Animals may benefit from high population density due to mate availability and predator risk dilution, but may also face increased competition in high density areas. These conflicting mechanisms should influence the pattern of change in population density between pre- and post-dispersal locations: do dispersing individuals choose to move to areas of higher or lower population density than that at their natal site? We examined the influence of density on dispersal in brush mice (Peromyscus boylii). We documented pre- and post-dispersal locations of individuals using both radio telemetry and live-trapping, and used a spatially explicit capture–recapture model to estimate density across the landscape. We also tested for a relationship between dispersal distance and local population density at the natal site. Animals tended to settle in areas with higher population densities than where they were born. This pattern held when landscape-level changes in population density were incorporated: the magnitude of change in local population density between the pre- and post-dispersal locations of a given individual tended to be greater than would be explained by increasing population density across the landscape alone. Further, dispersal distances were shorter when local natal population density was higher.

Differential larval responses of two ecologically similar insects (Odonata) to temperature and resource variation

How species respond to shifting environmental conditions is a central question in ecology, especially because ecosystems are experiencing rapidly changing climatic conditions. However, predicting the responses of species interactions and community composition to changing conditions is often difficult. We examined the effects of rearing temperature and resource level on larval survival of two ecologically similar dragonflies, Erythemis collocata and Pachydiplax longipennis. Within high and low (26 and 21°C) temperatures, we crossed species and resource level and reared larvae individually. We predicted that warmer temperatures would reduce survival and increase growth rate, that higher resource availability would increase survival and growth rate, and that the two species would respond similarly. We found that increased temperature reduced survival for both species. There was also an interaction between temperature and species: E. collocata had higher survival at the lower temperature, but lower survival at the higher temperature when compared to P. longipennis. Resource level did not affect survival. In general, P. longipennis grew more than E. collocata, with no effects of temperature or resource level. These results suggest that these species respond dissimilarly to changing thermal conditions, that increased food availability cannot always compensate for the negative effects of higher temperatures, and that climate change may affect interactions between these two sympatric, ecologically similar species, with potential consequences for community composition.

Effects of sex and population density on dispersal and spatial genetic structure in brush mice

Abstract Natal dispersal, the process of moving between the natal site and the site of 1st reproduction, affects a variety of ecological and evolutionary processes. Multiple factors have been suggested to influence patterns of natal dispersal in vertebrates; sex and population density are 2 of the most frequently invoked. In mammals, males are typically expected to disperse farther or more frequently than females. In contrast, theoretical predictions about the effect of population density are less clear, and support exists for both positive and negative density-dependent dispersal. Here, I investigate the influences of sex and population density on dispersal distances and spatial genetic structure (SGS) in the brush mouse (Peromyscus boylii), using both intensive field surveys and spatial genetic autocorrelation methods. Neither density nor sex affected dispersal distances. I did detect increased genetic structure in females compared to males, a pattern consistent with male-biased dispersal. However, processes other than dispersal can generate SGS, and I suggest that in addition to sex-biased dispersal, these results also could reflect gene dispersal via mating excursions. No clear effect of population density on either dispersal distance or SGS emerged. These results highlight the importance of using multiple methodologies to investigate dispersal. Resumen Dispersión natal, el proceso de traslado entre el sitio de nacimiento y el sitio de la primera reproducción, afecta una variedad de procesos ecológicos y evolutivos. Se han sugerido múltiples factores que pueden influenciar los patrones de dispersión natal en vertebrados; el sexo y la densidad de la población son los 2 factores más frecuentemente invocados. En los mamíferos, típicamente se espera que los machos se dispersen más lejos y más frecuentemente que las hembras. En contraste, las predicciones teóricas acerca del efecto de la densidad poblacional no son tan claras, y existe apoyo para ambas formas de dispersión dependiente de la densidad, positiva y negativa. Aquí, investigo la influencia del sexo y la densidad poblacional en las distancias de dispersión y la estructura genética espacial en el ratón de maleza (Peromyscus boylii), usando estudios de campo intensivos y métodos de auto correlación genética. Ni la densidad ni el sexo afectaron la distancia de dispersión. Detecté una elevada estructura genética de las hembras comparada con la de los machos, un patrón consistente con la expectación típica de la dispersión masculina. Sin embargo, procesos diferentes a la dispersión pueden generar estructura genética espacial, y yo sugiero que además a la dispersión sesgada por sexo, los resultados también pueden reflejar dispersión de genes a través de excursiones de apareamiento. No se apreciaron efectos de la densidad poblacional en la distancia de dispersión o en la estructura genética espacial. Estos resultados demuestran la importancia del uso de múltiples métodos para investigación la dispersión.

Comparison of Morphological Versus Molecular Characters for Discriminating Between Sympatric Meadow and Prairie Voles

Abstract Prairie (Microtus ochrogaster) and meadow (M. pennsylvanicus) voles are morphologically very similar species of rodents that are often found sympatrically. To assess the reliability of morphological characters typically used to differentiate between these two species, we compared the concordance of species identification based on morphological characteristics with identifications based on a species-specific difference within the avpr1a gene. We found that intraspecific variation in morphological characteristics resulted in erroneous or ambiguous species identification in the field (generally ≤5%) as well as for preserved specimens (up to ∼45%). Our data suggests that genotyping putative M. ochrogaster and M. pennsylvanicus at their avpr1a locus may be warranted for some individuals to ensure accurate species identification.