The effects of castration, sex ratio and population density on social segregation and habitat use in Soay sheep

We analysed 16 years of census data gathered on the island of Hirta (archipelago of St. Kilda) to investigate the effects of castration, population density, sex ratio, season and group type on habitat use and social segregation of Soay sheep. From 1978 to 1980, 72 male lambs were castrated. We used this experiment to study how a change in reproductive status could affect sociality and habitat choice of these males. Males, females and castrates were all segregated outside the rutting season in autumn. Castrates were the least segregated from females in spring and summer but were most segregated from them during the pre-rut. The more equal the sex ratios, the higher was the degree of social segregation. The three sex classes used similar habitat types, namely, Holcus agrostis, Agrostis festuca and Calluna habitats. Holcus agrostis and Agrostis festuca were top- and second-ranked in female and castrate habitat use, while Holcus agrostis and Calluna were the two top habitat types used by rams. It is unclear why males included Calluna heath habitats, but it cannot be excluded that they might have shifted their use depending on forage availability. A lack in differences in habitat use between castrates and females suggests that body size differences alone cannot be the driving factor for habitat segregation in male and female Soay sheep and that there are reasons other than body size that could motivate reproductive males to use additional habitat types, such as Calluna heath. Although habitat use shifted from one habitat type to the next between low- and high-population-density years and between seasons, there was no clear link between population density and how different groups (male, female or castrate) used these areas. We discuss effects of reproductive status, population density and sex ratio on social segregation and habitat use and suggest that these factors need to be taken into account when investigating causes of sexual segregation in ungulates.     

Territory and group sizes in Eurasian beavers (Castor fiber): echoes of settlement and reproduction?

According to current theories of territoriality, an animal is expected to defend the smallest area that can provide resources for maximisation of reproduction, known as the economically defendable area. In group territorial species however, the strategies behind resource defence are likely to be more complex with corporate territoriality, cooperative breeding, delayed dispersal and intra-group competition all potentially playing a role. Here we examined group territoriality in a social herbivorous rodent, the Eurasian beaver Castor fiber. Beavers in our study do not inhabit economically defendable territories. Instead the sequence of arrival of pairs into unoccupied areas seems to play a more important role in determining the size of the territory, whereas group size is determined by past reproductive success. We argue that the settlement pattern and reproductive history have a lasting impact in the territorial system of beavers due to a combination of the low adult mortality, high dispersal costs, and avoidance of resource depletion.R.D. Campbell and F. Rosell contributed equally to this work     

Optimal maternal investment in the dung beetle<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>?

Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne     

Cost-effective forest conservation and criteria for potential conservation targets: a Finnish case study

Selecting reserves for forest biodiversity maintenance is often done by setting criteria for components of structural elements of biodiversity, such as a volume of decaying wood. We tested how the different threshold values for the components of structural elements affect the cost-effective site selection. Using Finnish National Forest Inventory information and remote sensing data, we determined a habitat quality index and economic value for each site in Satakunta region in Finland. Moreover, we defined several sets of potential conservation targets using alternative criteria for the habitat quality index developed for the Finnish case study. These figures were used in the site selection model in order to maximize the sum of habitat index of selected areas under a given budget constraint. We found that the production possibility frontier for the outputs of timber and biodiversity is only slightly concave when using the given threshold values. Thus, the optimal combination of the outputs is sensitive to the relative values of these goods. Our results suggest that an integrated approach in forest conservation could provide to environmental managers considerable cost savings compared with current management practices. Environmental managers could also reduce conservation costs by loosening the criteria for potential conservation targets. This would not lower considerably the quality of conserved forests.     

Divergent evolution of feeding substrate preferences in a phylogenetically young species flock of pupfish (Cyprinodon spp.)

A fundamental question in sympatric speciation is how trophic divergence is achieved. We used an extremely young (<8,000 years) species flock of pupfish (Cyprinodon spp.) from Laguna Chichancanab in south-eastern Mexico to examine divergent evolution of preferences for different feeding substrates. In a test aquarium, we presented four feeding substrates (sand, gravel, a plastic plant, and blank bottom), but no actual food was offered. The four feeding substrates were chosen to mirror the most common substrate types in Laguna Chichancanab. Previous studies demonstrated that benthic food items prevail in the diet of most Cyprinodon species. C. beltrani preferred sand, whereas C. labiosus preferred gravel. F₁ hybrids of both species showed intermediate preferences. C. maya searched for food equally at all substrates. As the test fish were reared under identical laboratory conditions (i.e., in the absence of feeding substrates), the species-specific preferences appear to be genetically fixed, suggesting rapid divergent evolution of feeding behaviors.     

Changes in Upland Wildlife Habitat on Farmland in Illinois 1920–1987

/ An index of upland wildlife habitat was developed to investigate patterns and changes in habitat over time, using four years (1920, 1940, 1964, 1987) and the state of Illinois as an example. The index was composed of two subdivisions that described, at the county level, the quantity of wildlife habitat and a third subdivision that described farming disturbances that impacted the quality of the habitat. Data came from the US Census of Agriculture. The first subdivision that reflected quantity of habitat was called the wildlife habitat subdivision and was the sum of percentage woodland on farms, percentage farmland in nonrow crops, and percentage farmland in set-aside programs. The second subdivision that reflected the quantity of habitat was termed the soil-related features subdivision and was the sum of the percentage of farmland that was not highly erodible, the percentage of farmland in soil-protecting crops, and the percentage of farmland in conservation tillage. The third subdivision, reflecting the quality of the habitat, was the farming disturbance subdivision and was the sum of the percentage of grazing and the percentage of land on which fertilizers, pesticides, and herbicides were applied. Overall, major decreases occurred between 1920 and 1987 in the subdivisions reflecting the quantity of wildlife habitat and a major increase occurred in the subdivision associated with farming disturbance, reflecting the intensification of agriculture in the state. However, there was variability throughout the state, with some counties being more favorable to wildlife (as measured by the subdivisions) than others. Most of the changes within the state for the subdivisions reflecting quantity of upland wildlife habitat occurred during 1940 while changes in the farming disturbance subdivision (reflecting habitat quality) occurred in 1964. By 1987, the western and southern parts of Illinois were the most favorable for wildlife as reflected in all three subdivisions. Upland wildlife harvest indices were related to the subdivisions in 1964 and 1987, when harvest indices were available. Cottontail and northern bobwhite harvests were higher in counties with higher amounts of the wildlife habitat subdivision in both years. Cottontail harvest was also higher in counties with lower levels of the farming disturbance subdivision in 1964 and higher levels of soil-related features subdivision in 1987. Indices at the county level have the potential to be used in a multiscale analysis to investigate the impact of policy changes on large-scale areas of the Midwest and to develop regional perspectives of the impacts of agriculture on upland wildlife and their habitats.KEY WORDS: Upland wildlife; Habitat; Agriculture; Illinois     

Habitat selection models to account for seasonal persistence in radio telemetry data

Models for the analysis of habitat selection data incorporate covariates in an independent multinomial selections model (McCracken et al. 1998) Ramsey and Usner 2003 and an extension of that model to include a persistence parameter (2003). In both cases, all parameters are assumed to be fixed through time. Radio telemetry data collected for habitat selection studies typically consist of animal relocations through time, suggesting the need for an extension to these models. We use a Bayesian approach that allows for the habitat selection probabilities, persistence parameter, or both, to change with season. These extensions are particularly important when movement patterns are expected to differ seasonally and/or when availabilities of habitats change throughout the study period due to weather or migration. We implement and compare the models using radio telemetry data for westslope cutthroat trout in two streams in eastern Oregon.     

Effects of increased vegetation cover on nesting behavior of sticklebacks (Gasterosteus aculeatus)

To maximize reproductive success, reproductive behaviors have to be adjusted to environmental conditions. The breeding habitats of the threespine stickleback Gasterosteus aculeatus are presently changing in the Baltic Sea due to eutrophication and enhanced growth of filamentous green algae. Earlier studies show that high algae density reduces mate encounter rate and the intensity of selection on a few sexually selected traits, but the willingness of males to nest under the new conditions, and their investment into reproduction, have not been investigated. Here, we investigated the effect that increased algae growth has on nesting behavior of sticklebacks. We allowed males to build nests in aquaria with either a sparse or a dense vegetation structure and recorded male nest building behavior and nest characters. Males that nested in dense vegetation showed a longer latency before commencing nest building and also completed nest building later since there was no difference in time spent building. There was no effect of vegetation cover on nest characters. These results suggest that males prefer to nest in sparser vegetation, but that they eventually nest in dense vegetation if more open habitats are not available. This may arise from a negative effect of vegetation on visibility and mate encounter rate and thus on expected reproductive success. This implies that human-induced changes in the environment may force sticklebacks to breed in non-preferred habitats. Since the intensity of sexual selection is reduced in these areas, this could influence the further evolution of the population.     

Metapopulation dynamics of a perennial plant, Succisa pratensis, in an agricultural landscape

Most metapopulation models neglect the local dynamics, and systems characterized by slow population turnover, time lags and non-equilibrium, are only rarely examined within a metapopulation context. In this study we used a realistic, spatially explicit, dynamic metapopulation model of a long-lived grassland plant, Succisa pratensis, to examine the relative importance of local population dynamics, and short and long-distance dispersal of seeds.     

The spatial links tool: Automated mapping of habitat linkages in variegated landscapes

The removal, alteration and fragmentation of habitat in many parts of the world has led to a loss of biodiversity. Within the prevailing societal limitations the process is not easily reversed. Attempts are being made to minimise the fragmentation of remaining habitat by strategically reversing or managing habitat loss. Although their relative usefulness is a topic of debate among ecologists, habitat corridors are seen as one way of maintaining spatially dependent ecological processes within landscapes where habitat has been seriously depleted. Corridors can only be effective if they significantly contribute to the species sustaining processes of gene flow, resource access or the colonisation of vacant patches. We present a spatial habitat modelling methodology for evaluating the contribution and potential contribution of connecting paths to landscape connectivity. We have developed the spatial links tool (SLT), which maps link value across a region. The SLT combines connectivity measures from metapopulation ecology with the least cost path algorithm from graph theory, and can be applied to continuously variable landscape data. Combined with expert judgement, link value maps can be used to delineate habitat corridors. The approach capitalises on some synergies between ecological relevance and computational efficiency to produce an easily applied heuristic tool that has been successfully applied in NSW Australia.