Aspects Of Population Ecology Research Articles

Sexual and parent–offspring dietary segregation in a colonial raptor as revealed by stable isotopes

AbstractDiet composition and foraging behaviour may show considerable variation among population groups (such as sex and age classes), with potentially important consequences for population dynamics. Thus, failure to account for intra‐specific differences in trophic ecology can bias our understanding of different aspects of population ecology and limit the implementation of effective management and conservation strategies. Although countless studies have investigated the diet of birds, comparatively few have tried to describe intra‐specific sources of dietary variation. Here, we used stable isotope analysis (SIA) to investigate sex‐ and age‐related dietary segregation in the lesser kestrel Falco naumanni breeding in South Iberia and to discuss potential mechanisms involved in such segregation. Females had a narrower isotopic niche width and significantly more depleted δ13C signatures than males during the courtship period, likely due to a higher consumption of energetically rich mole crickets. Our results suggest that sex‐specific differences in the diet of lesser kestrels do not result from intra‐specific competition and are unlikely to be explained by sexual size dimorphism alone. Instead, the main driving force of observed sexual segregation appears to be the different energetic requirements of males and females before laying, when females need a higher allocation of resources to egg production. δ15N isotopic signatures differed significantly between adults and chicks and niche overlap between these age classes was low. Stable isotopic mixing models showed that, compared to adults, the diet of chicks was less diverse and mainly dominated by grasshoppers. Different resource allocation between chicks and adults might also result from different energy requirements, as rapidly growing chicks require more energy than adults, ultimately leading to a parent–offspring dietary segregation. Finally, overall agreement between pellet analysis and SIA methods highlight the potential of SIA for assessing intra‐specific variation in dietary regimes which is often unfeasible through conventional approaches of diet assessment.

A test of niche centrality as a determinant of population trends and conservation status in threatened and endangered North American birds

Abundance and other aspects of population ecology have long been known to con- tribute to shaping the geography of species' distributions. In particular, abundance patterns have recently been shown to negatively correlate with environmental distance from conditions in the center of a species' abiotic niche, rather than vary with distance from the geographic center of a species' distribution. We tested for such associations across 8 species of endangered or threatened bird species in North America using population trend data derived from >4 decades of North Amer- ican Breeding Bird Surveys. Although we found no consistent overall pattern, we did observe nega- tive population trends at conditions that were the most extreme within species' niches. This suggests that niche peripherality is a relevant factor to consider in conservation planning. Specifi- cally, environmentally peripheral sites may be poor places in which to protect populations of endan- gered and threatened species, irrespective of how centrally they may occur within species' geo- graphic distributions.

Meiotic behavior and pollen viability of wild populations of the neotropical species Vriesea gigantea (Bromeliaceae)

AbstractPlant fertility can influence many aspects of population ecology and evolution. The quantity and quality of pollen produced by a plant is an important component of reproductive success. Plant fertility was analyzed by assessing: chromosome number, meiotic behavior and pollen viability of seven native populations of Vriesea gigantea. All plants presented 2n = 50 chromosomes. Most of the pollen mother cells showed a regular meiotic behavior with 25 bivalents and regular chromosome segregation. In accordance, high pollen viability (84–98%) was recorded for all investigated populations. These results indicated that plants from all populations analyzed are fertile. Despite the overall high pollen viability, significant differences were detected among populations. The population of Praia do Araçá showed a reduced percentage of pollen viability, although meiosis was quite regular. Reduction in pollen viability could have an important effect on plants fertility and, consequently, on fitness of this population.

Aspects of population ecology in two populations of fiddler crabs, Uca pugnax

Fiddler crabs, Uca pugnax, were collected from a highly contaminated site and a relatively clean site, both in New Jersey to determine if and how environments with varying levels of pollutants may impact aspects of population biology including individual size, morphology (major cheliped size), population density, fecundity, recruitment and survivorship of early benthic phases. Crabs from the highly contaminated site were significantly larger in size, but had lower population density, lower recruitment, reduced reproductive season and lower survivorship of early benthic phases. Our study suggests that contamination may play a role in population ecology of U. pugnax. This study also determined that the reproductive season for U. pugnax in New Jersey is much longer than reported in the literature and could potentially be impacted by global climate change.