Increased searching and handling effort in tall swards lead to a Type IV functional response in small grazing herbivores

Understanding the functional response of species is important in comprehending the species’ population dynamics and the functioning of multi-species assemblages. A Type II functional response, where instantaneous intake rate increases asymptotically with sward biomass, is thought to be common in grazers. However, at tall, dense swards, food intake might decline due to mechanical limitations or if animals selectively forage on the most nutritious parts of a sward, leading to a Type IV functional response, especially for smaller herbivores. We tested the predictions that bite mass, cropping time, swallowing time and searching time increase, and bite rate decreases with increasing grass biomass for different-sized Canada geese (Branta canadensis) foraging on grass swards. Bite mass indeed showed an increasing asymptotic relationship with grass biomass. At high biomass, difficulties in handling long leaves and in locating bites were responsible for increasing cropping, swallowing, and searching times. Constant bite mass and decreasing bite rate caused the intake rate to decrease at high sward biomass after reaching an optimum, leading to a Type IV functional response. Grazer body mass affected maximum bite mass and intake rate, but did not change the shape of the functional response. As grass nutrient contents are usually highest in short swards, this Type IV functional response in geese leads to an intake rate that is maximised in these swards. The lower grass biomass at which intake rate was maximised allows resource partitioning between different-sized grazers. We argue that this Type IV functional response is of more importance than previously thought

Biodiversity conservation: history, protected areas and hotspots

Angola is a large country of great physiographic, climatic and habitat diversity, with a corresponding richness in animal and plant species. Legally protected areas (National Parks and Game Reserves) were established from the 1930s and occupied 6% of the country’s terrestrial area at the time of independence in 1975. As a consequence of an extended war, the Protected Areas were exposed to serious neglect, poaching and land invasions. Many habitats of biogeographic importance, and many rare and endemic species came under threat. The recently strengthened administration gives cause for optimism that a new era for biodiversity conservation is at hand. The Protected Areas system was greatly expanded in 2011, and increasing resources are being made available towards achieving management effectivenessinfo:eu-repo/semantics/publishedVersio

Seasonal and Ontogenetic Changes in Movement Patterns of Sixgill Sharks

Understanding movement patterns is fundamental to population and conservation biology. The way an animal moves through its environment influences the dynamics of local populations and will determine how susceptible it is to natural or anthropogenic perturbations. It is of particular interest to understand the patterns of movement for species which are susceptible to human activities (e.g. fishing), or that exert a large influence on community structure, such as sharks.We monitored the patterns of movement of 34 sixgill sharks Hexanchus griseus using two large-scale acoustic arrays inside and outside Puget Sound, Washington, USA. Sixgill sharks were residents in Puget Sound for up to at least four years before making large movements out of the estuary. Within Puget Sound, sixgills inhabited sites for several weeks at a time and returned to the same sites annually. Across four years, sixgills had consistent seasonal movements in which they moved to the north from winter to spring and moved to the south from summer to fall. Just prior to leaving Puget Sound, sixgills altered their behavior and moved twice as fast among sites. Nineteen of the thirty-four sixgills were detected leaving Puget Sound for the outer coast. Three of these sharks returned to Puget Sound.For most large marine predators, we have a limited understanding of how they move through their environment, and this clouds our ability to successfully manage their populations and their communities. With detailed movement information, such as that being uncovered with acoustic monitoring, we can begin to quantify the spatial and temporal impacts of large predators within the framework of their ecosystems

Trophic ecology of two savanna grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou

The feeding niches and trophic ecology of two South African grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou, are compared using stable carbon and nitrogen isotope data from feces and tooth dentine collagen. As sympatric, closely related taxa predicted to occupy similar trophic positions, the blue and black wildebeest provide a good model for studying the mechanisms of coexistence and macroevolution in mammals. Data from feces collected from a single reserve in the Free State Province reveal different trophic behaviors between two herds of blue wildebeest and between both compared with a single herd of black wildebeest. These data suggest that sympatric coexistence of blue and black wildebeest is facilitated by differential niche occupation at family group or herd levels, rather than between species. However, such separation does not occur over longer time scales: results from dentine collagen support the hypothesis that the two species are indistinct in terms of trophic behavior, although blue wildebeest show more feeding flexibility, probably because of their wider habitat tolerance range. Similarities in premaxillary width of males and females of both species also suggest that both species are adapted to similar feeding styles. Thus, it is unlikely that changes in trophic behavior provided the trigger for divergence of the black from the blue wildebeest lineage in the Middle Pleistocene. We argue that the case of these two species represents an example of speciation that was not driven by resource competition, as is often assumed for many turnover events in mammalian evolution. We briefly discuss a previous suggestion that links black wildebeest evolution to their more territorial breeding behavior associated with Middleto-Late Pleistocene landscape changes in southern Africa

Global environmental controls of diversity in large herbivores

Large mammalian herbivores occupy half of the earth's land surface and are important both ecologically and economically, but their diversity is threatened by human activities. We investigated how the diversity of large herbivores changes across gradients of global precipitation and soil fertility. Here we show that more plant-available moisture reduces the nutrient content of plants but increases productivity, whereas more plant-available nutrients increase both of these factors. Because larger herbivore species tolerate lower plant nutrient content but require greater plant abundance, the highest potential herbivore diversity should occur in locations with intermediate moisture and high nutrients. These areas are dry enough to yield high quality plants and support smaller herbivores, but productive enough to support larger herbivores. These predictions fit with observed patterns of body size and diversity for large mammalian herbivores in North America, Africa and Australia, and yield a global map of regions with potentially high herbivore diversity. Thus, gradients of precipitation, temperature and soil fertility might explain the global distribution of large herbivore diversity and help to identify crucial areas for conservation and restoration.