Two experimental tests of the relationship between group stability and aggressive conflict in Polistes wasps

Two field experiments were used to examine how the relative benefits of cooperation influence within-group conflict in foundress associations of the paper wasp Polistes dominulus. P. dominulus foundresses can either nest alone or cooperate with other foundresses. We experimentally manipulated the relative benefits of co-foundress associations vs independent reproduction and tested the effect on aggressive within-group conflict. First, we examined aggression between alpha and beta co-foundresses before and after lower-ranking foundresses were removed. Removal of subordinates increases the relative contributions of the remaining subordinates to group reproductive output as there are fewer adults to care for the brood. Transactional models predict that group conflict over reproductive shares will increase as the relative benefits of grouping increase. As predicted, aggression between the co-foundresses significantly increased following subordinate removal. Second, we experimentally reduced ecological constraints on independent nesting by placing a previously orphaned, adoptable nest comb near the occupied nests. Providing an independent breeding opportunity is predicted to increase the benefits of independent reproduction relative to those of cooperating, thereby reducing group stability and aggression. As predicted, aggression between dominant and subordinate foundresses significantly decreased after the orphaned comb was presented. Therefore, group members sense variation in ecological constraints and relative productivity contributions and quickly modulate their behavior in response. Overall, these two experiments suggest that paper wasps behave as if within-group competition is limited by the threat of group dissolution such that stable groups where cooperation is strongly favored can withstand higher levels of conflict than unstable groups.     

GIS-based niche modeling for mapping species' habitat

Ecological "niche modeling" using presence-only locality data and large-scale environmental variables provides a powerful tool for identifying and mapping suitable habitat for species over large spatial extents. We describe a niche modeling approach that identifies a minimum (rather than an optimum) set of basic habitat requirements for a species, based on the assumption that constant environmental relationships in a species' distribution (i.e., variables that maintain a consistent value where the species occurs) are most likely to be associated with limiting factors. Environmental variables that take on a wide range of values where a species occurs are less informative because they do not limit a species' distribution, at least over the range of variation sampled. This approach is operationalized by partitioning Mahalanobis D2 (standardized difference between values of a set of environmental variables for any point and mean values for those same variables calculated from all points at which a species was detected) into independent components. The smallest of these components represents the linear combination of variables with minimum variance; increasingly larger components represent larger variances and are increasingly less limiting. We illustrate this approach using the California Gnatcatcher (Polioptila californica Brewster) and provide SAS code to implement it.     

Evaluation of Urban Sustainability in Specific Sectors in Latvia

In Latvia, the concept of sustainability is only slowly gaining recognition. An analysis of Development Plans prepared by the four largest cities of Latvia indicates that sustainability is presented as one of the guiding principles. However, a comparison of Development Plan policies against the urban sustainability issues reveals a great deal of ambiguity and contradiction.At the municipal level, planners and politicians lack indicators to gauge whether the long-term goals of Development Plans and the principles of sustainable development are being achieved. As a consequence, the broad public is deprived of the opportunity to assess for itself the process of development in relation to Development Plan policies, thus limiting accountability in development decision-making. Relevant statistical data collected on a regular basis are required to create sustainability indicators reflecting sustainability issues, to supplement and replace existing statistical compilations pertaining almost exclusively to economic growth and consumption. Development and utilisation of sustainability indicators can be an effective instrument for promoting the values of sustainable development amongst politicians, planners and the broad public and for enhancing accountability in decision-making.     

Site fidelity of male Galápagos sea lions: a lifetime perspective

Knowledge about the distribution of resources can lead to the development of spatial preferences and long-term site fidelity. Individuals are expected to choose sites that best suit their needs. However, dominant individuals restrict movements of less competitive ones. Accordingly, one may expect spatial preferences to differ with regard to individual characteristics and to change over time. We investigated lifetime changes of site fidelity patterns with regard to reproductive success in male Galápagos sea lions (Zalophus wollebaeki). Showing a high degree of natal philopatry in the first 2 years of life, non-territorial males pass through a stage of fidelity to their natal colony where they develop preferences for areas outside prime breeding areas. Variation in the degree of spatial preferences was not associated with age or size, characteristics linked to an individual’s dominance status. For non-territorial males, roaming proved to be an adequate strategy to gain reproductive success. Only the most competitive males established territories in areas preferentially visited by females. They had a high probability to return to breeding areas where they successfully reproduced in previous seasons. Overall, the results reveal lifetime changes in site fidelity with regard to male status. The degree of site fidelity observed within the colony suggests familiarity and thus a high degree of tolerance among individuals using the same areas. This seems to facilitate attendance in the colony and thus the possibility to prospect for oestrus females.     

A novel application of Approximate Bayesian Computation for detecting male reproductive advantages due to mating order

Studies of the effects of mating order on fertilization success, classically analyzed as the proportional paternity of the second male, have advanced our understanding of the relative influences of postcopulatory male–male competition and female choice on sexual selection. However, results from these studies are often difficult to analyze because (1) distributions of offspring per dam rarely follow a normal distribution and (2) proportional paternities are never normally distributed. Previous studies partially account for these limitations by using nonparametric statistics. However, behavioral studies are often plagued by relatively small sample sizes and require a more powerful analytical approach. Here, we develop a new analytical framework for studying fertilization bias. Our Approximate Bayesian Computational (ABC) model overcomes many of the limitations of currently employed methods. We apply our model to analyze the effects of male mating order on paternity success in the brown anole lizard, Anolis sagrei. Using our ABC simulation, we find a marked first-male advantage: first males sired approximately 80 % of the offspring in our study. Next, based on re-analysis of four previously published datasets, we show that traditional statistical methods often over- or underestimate biases related to mating order. Moreover, by comparing our model to more traditional statistical tests, we show that the ABC method is robust to relatively small samples sizes and should therefore be useful for studying mating-order effects in a variety of systems. Our model is implemented as an R package, ABCp2, and is freely available for use.     

IMPACTS OF URBAN LANDUSE ON MACROINVERTEBRATE COMMUNITIES IN SOUTHEASTERN WISCONSIN STREAMS1

ABSTRACT: Macroinvertebrates were used to assess the impact of urbanization on stream quality across a gradient of watershed imperviousness in 43 southeastern Wisconsin streams. The percentage of watershed connected imperviousness was chosen as the urbanization indicator to examine impact of urban land uses on macroinvertebrate communities. Most urban land uses were negatively correlated with the Shannon diversity index, percent of pollution intolerant Ephemeroptera, Plecoptera, and Trichoptera individuals, and generic richness. Nonurban land uses were positively correlated with these same metrics. The Hilsenhoff biotic index indicated that stream quality declined with increased urbanization. Functional feeding group metrics varied across a gradient of urbanization, suggesting changes in stream quality. Proportions of collectors and gatherers increased, while proportions of filterers, scrapers, and shredders decreased with increased watershed imperviousness. This study demonstrated that urbanization severely degraded stream macroinvertebrate communities, hence stream quality. Good stream quality existed where imperviousness was less than 8 percent, but less favorable assessments were inevitable where imperviousness exceeded 12 to 20 percent. Levels of imperviousness between 8 and 12 percent represented a threshold where minor increases in urbanization were associated with sharp declines in stream quality.     

Coping with chaos: unpredictable food supplies intensify torpor use in an arid-zone marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata)

The severity, duration and amplitude of extreme weather events are forecast to intensify with current climate trends, over both long (e.g. seasonal) and short (e.g. daily) time-scales. As such, the predictability of food supplies for many small endotherms is likely to become increasingly important. Numerous small mammals and birds combat food shortages using torpor, a controlled reduction in metabolic rate and body temperature that helps lower their daily energy requirements. As such, torpor often has been cited as a key feature allowing some small endotherms to survive highly unpredictable climates, such as tropics or dry deserts, but mensurative demonstrations of this are lacking. We have shown here that when a small desert marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata), is offered unpredictable levels of daily food, they increase frequency of daily torpor and length of bouts compared with animals offered ad libitum food, but this was not found for animals offered a 70% food-restricted diet. Our data suggest that simple food restriction may not be sufficient for evaluating the efficacy of torpor as a strategy for managing unpredictable climates.