Resource-rich Habitats Research Articles

TOP PREDATORS CONSTRAIN THE HABITAT SELECTION GAMES PLAYED BY INTERMEDIATE PREDATORS AND THEIR PREY

Effects of predators on prey habitat selection, and reciprocal effects of prey on predator habitat selection, have been analyzed using game theory. In the absence of predators, models predict that prey (e.g., herbivores) will aggregate strongly in habitats where their resources (e.g., plants) are abundant. However, game theoretic models predict that in the presence of predators, prey use of resource-rich habitats declines. Paradoxically, it is instead predators that are predicted to be mostly strongly aggregated in areas where the prey's resources (plants) are abundant, even though the predators themselves do not utilize these resources. This striking result has been dubbed the leapfrog effect by Sih (1998, 2004). Here I explore the possibility that predictions for predator and prey habitat selection are sensitive to the assumption that predators forage free from any predation risk of their own. I contrast the predictions of a 3-trophic level model with those of a 4-trophic level model, and show that in...

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PLANT SCIENCE Is it better to grow efficiently within a limited range of conditions or safely across a broader range? Factors that influence this choice are illustrated by comparing water-conducting tissues (xylem) in plants. Wide and long vessels support low-resistance flow of water, but are susceptible to catastrophic failure provoked by a few untoward bubbles. Narrower, shorter xylem vessels struggle to carry as much water, but are a more robust conduit for facing the vagaries of life. Because transpiration and photosynthesis go hand in hand, the amount of water delivered to the leaves determines the amount of photosynthesis that can be supported. Kocacinar and Sage, examining xylem structure in relation to metabolism and environment, find that some species favor a secure water supply and others favor a maximized water supply that supports more leaf area. An increased leaf canopy is a competitive solution in resource-rich habitats, whereas reliability of water supply is the solution favored for species growing in drought-prone habitats. In either case, C4 photosynthetic plants, which use water more efficiently than do C3 photosynthetic plants, have the advantage of being able to go further with a given amount of xylem tissue. Thus, the advantages of C4 metabolism include not only metabolic efficiency, but also doing more with less in plant infrastructure. — PJH Plant Cell Environ. 26 , 2015 (2003).

The effect of apical dominance on the branching architecture of Arctostaphylos uva-ursi in four contrasting environments

We studied horizontal spreading and axillary bud activation of colonizing branches of a clonal dwarf shrub, Arctostaphylos uva-ursi, in SW Finland in four habitats with varying pollution, nutrient, light and competition levels. A. uva-ursi showed high plasticity in the proportion of released buds, which changed according to the stress and resource level of the habitats. Apical dominance of lateral branching was the strongest in the resource-poor habitats (low soil nutrient or low light levels). However, when the apex of the parent shoot was terminated (due to mortality of an apical bud or the formation of an inflorescence) the disruption of apical dominance caused intensive branching in the poor habitats. Apical dominance of the dominant shoots was much weaker in the resource-rich habitats. When nutrient availability and light level were relatively high, branching frequency was high in both intact (expanded) and terminated parent shoots. Shoot mortality and the proportion of terminated shoot apices was the highest in the polluted habitat, as a result of soil toxicity. This caused intensive branching in all shoot hierarchies, which may enhance the plant’s survival in heavy metal polluted soil. We conclude that plastic branching enables this species to recover after damage, or to respond to changed resource levels according to the ‘reserve meristem hypothesis’. The branching response to different environmental conditions was simulated by means of an L-system architectural model based on the demographic and morphological parameters measured in each habitat.

Social and genetic analysis of a population of free-living cats (Felis catus L.) exploiting a resource-rich habitat

Free-living cats (Felis catus L.) exploiting a waste-disposal site in rural Australia were studied for two years to investigate population structure and dynamics, and the relatedness of constituent individuals. The density of the population was equivalent to 700–750 cats km–2, the sex ratio was heavily skewed towards males, breeding occurred from July to April, and kitten survival rates were low. A combination of observational data, biometrics and microsatellite loci analyses was used to assess the relatedness of individuals in the population; these methods yielded highly congruent results. Thus, a female kin-group of three was identified, there was no female immigration, the average relatedness amongst the population was high and there was no indication of male dominance. The results indicate that cats at the site formed a tightly structured group, rather than an ad hoc collection of individuals. The stable, resource-rich habitat of waste-disposal sites may generally support high densities of group-forming cats in rural Australia, and pose broad-scale but previously unrecognised problems for effective management of free-living cats.

Land use changes and the decline of farmland wildlife: An appraisal of the set-aside approach

Declines in the distribution and abundance of many wildlife groups associated with agricultural ecosystems have been documented across Europe. The increasing body of evidence suggests that the processes of intensification of production have been responsible for many of these losses. The widespread introduction of set-aside throughout Europe from the mid-1980s was thought to have provided a mechanism by which to reduce the adverse effects of agricultural production techniques and produce benefits for farmland wildlife. In many instances this has not been the case and, in fact, the large-scale uptake of set-aside has seen the continuation of the decline of already threatened groups. However, although land abandonment from agriculture per se may not be universally valuable, correctly managed set-aside with precise environmental goals is believed to be a useful opportunity to provide resource-rich habitats for declining species. Examples are taken from the conservation biology of gamebirds and endangered annual arable wildflowers in the UK to demonstrate the adverse effects of agricultural intensification and the role of set-aside in the conservation biology of farmland wildlife.

Secondary sex ratio and maternal dominance rank among wild yellow baboons (Papio cynocephalus) of Mikumi National Park, Tanzania.

The Trivers and Willard model predicts that offspring of dominant mothers will be biased toward males and offspring of subordinate mothers towards females, whereas a local-resource-competition hypothesis predicts the reverse. Available data bearing upon these alternative predictions are inconsistent. It has been suggested that the local-resource-competition hypothesis will predominate when resources are scarce, and the Trivers-Willard hypothesis when resources are abundant. The relationship between maternal dominance and secondary sex ratio for 214 offspring of 61 females was examined using four troops of wild yellow baboons living in Mikumi National Park, where the population was increasing in a resource-rich habitat. For all troops combined, no significant relationship was found between offspring sex ratio and maternal rank. The four troops separately showed inconsistent trends, and in no case did the relationship reach conventional levels of statistical significance. In contrast, the local resource-competition hypothesis was supported by a study of yellow baboons done with one troop and 80 offspring in Amboseli National Park, where a massive population decline had occurred. The contrasting Amboseli and Mikumi results may be due to differences in resource-competition at the two study sites, or to stochastic variation. © 1992 Wiley-Liss, Inc.

Intra- and Interspecific Interactions in Low Density Populations in Resource-Rich Habitats

Parasites on the gills of marine fish are used to study intra- and interspecific interactions.(...) Evidence is given that most animals species are likely to occur at low densities in resource-rich habitats, and that conclusions based on the study of gill parasites can be applied to them. In particular, a discussion of a diversification equation modelled on the logistic equation for population growth shows that there is a vast number of vacant niches. The general conclusion is that the major problem for most animals is not to avoid competition but to find suitable sites for feeding and mating

Diet of the Mountain Pygmy-possum, Burramys parvus (Marsupialia: Burramyidae) and other small mamma ls in the alpine environment at Mt Higginbotham, Victoria.

The diets of Burramys parvus, Rattus fuscipes and Antechinus swainsonii in Podocarpus lawrencei heathland in alpine Victoria during the non-winter period were determined from analysis of 264 faecal pellets. Both frequency of occurrence and mean percentage composition of dietary items in the samples were determined; the Iatter being used to assess the diet. We found B. parvus to be an omnivore concentrating on insec ts. It eats a variety of foods but the Bogong Moth (Agrolis infusa) is heavily exploited (31 % of the composition of faecal samples) especially by females during the breeding season (46 %). Other components of the diet are other invertebrates, predominantly insects (32 %) and vegetative material (16 %). Seasonal differences in the composition of the diet of B. parvus were due to the exploitation of fruit in the non-breeding season. No differences in diet were observed between age-classes and the sexes but females are sedentary in food resource-rich habitats, whilst when not breeding, males occur in areas of poorer food resources. Circumstantial evidence suggests that during facultative hibernation a major dietary component of B. parvus may be seeds, cached from the previous summer-autumn. The diet of R. fuscipes consists mainly of insects (12 %) and the largest vegetative component was seeds (10.1 %). Fungi were found in 53 % of faecal samples of R. fuscipes but could not be quantified as a percentage composition of diet. The species is classified as a selective omnivore. The diet of A. swainsonii consisted of 68 % in sec ts, 10.4 % of insect setae and worms with the major vegetative component (5.2 %) being soft fruits. Burramys parvus, relative to the other small mammals with which it cohabits, has become a specialist in exploiting the abundant and rich food resource of Bogong moths.