Home About us Contact
|
Home About us Contact | ||
|
|
||
Consumer Species (consumer + species)
Selected AbstractsADAPTIVE CHANGE IN THE RESOURCE-EXPLOITATION TRAITS OF A GENERALIST CONSUMER: THE CEOLUTION AND COEXISTENCE OF GENERALISTS AND SPECIALISTSEVOLUTION, Issue 3 2006Peter A. Abrams Abstract Mathematical models of consumer-resource systems are used to explore the evolution of traits related to resource acquisition in a generalist consumer species that is capable of exploiting two resources. The analysis focuses on whether evolution of traits determining the capture rates of two resources by a consumer species produce one generalist, two specialists, or all three types, when all types are characterized by a common fitness function. In systems with a stable equilibrium, evolution produces one generalist or two specialists, depending on the second derivative of the trade-off relationship. When there are sustained population fluctuations, the nature of the trade-off between the consumer's capture rates of the two resources still plays a key role in determining the evolutionary outcome. If the trade-off is described by a choice variable between zero and one that is raised to a power n, polymorphic states are possible when n > 1, which implies a positive second derivative of the curve. These states are either dimorphism, with two relatively specialized consumer types, or trimorphism, with a single generalist type and two specialists. Both endogenously driven consumer-resource cycles, and fluctuations driven by an environmental variable affecting resource growth are considered. Trimorphic evolutionary outcomes are relatively common in the case of endogenous cycles. In contrast to a previous study, these trimorphisms can often evolve even when new lineages are constrained to have phenotypes very similar to existing lineages. Exogenous cycles driven by environmental variation in resource growth rates appear to be much less likely to produce a mixture of generalists and specialists than are endogenous consumer-resource cycles. [source] Diversity,stability relationships in multitrophic systems: an empirical explorationJOURNAL OF ANIMAL ECOLOGY, Issue 5 2003Priyanga Amarasekare Summary 1The relationship between diversity and stability is crucial in understanding the dynamics of multitrophic interactions. There are two basic hypotheses about the causal link between diversity and stability. The first is that fluctuations in resource abundance allow consumer coexistence, thus increasing diversity at the consumer trophic level (resource variability hypothesis). The second is that interactions between coexisting consumer species reduce consumer efficiency and dampen population fluctuations, thus increasing consumer,resource stability (consumer efficiency hypothesis). 2The two hypotheses lead to three comparative predictions: (i) fluctuations should be greater (resource variability) or smaller (consumer efficiency) in resource populations with coexisting consumer species, compared to those invaded only by the consumer species superior at resource exploitation; (ii) average resource abundance should be greater (resource variability) or smaller (consumer efficiency) in resource populations with greater fluctuations; and (iii) removal of the consumer species inferior at resource exploitation should increase or not affect resource population fluctuations (resource variability), or always increase them (consumer efficiency). 3I tested these predictions with data from a host,multiparasitoid community: the harlequin bug (Murgantia histrionica) and two specialist parasitoids (Trissolcus murgantiae and Ooencyrtus johnsonii) that attack the bug's eggs. 4Local host populations with coexisting parasitoids exhibited smaller fluctuations and greater average abundance compared to those with just Trissolcus, the species superior at host exploitation. Local populations that lost Ooencyrtus, the species inferior at host exploitation, exhibited an increase in host population fluctuations compared to those that did not. 5The results contradict the expectations of the resource variability hypothesis, suggesting that host population fluctuations are unlikely to be driving parasitoid coexistence. They are consistent with the consumer efficiency hypothesis, that interactions between coexisting parasitoid species dampens host population fluctuations. I discuss the implications of these results as well as possible caveats. [source] Predators, parasitoids and pathogens: species richness, trophic generality and body sizes in a natural food webJOURNAL OF ANIMAL ECOLOGY, Issue 1 2000J. Memmott Summary 1.,A food web is presented which describes trophic interactions among the herbivores, parasitoids, predators and pathogens associated with broom, Cytisus scoparius (L.) Link. The data come from published work on the community at a single site. The web comprises a total of 154 taxa: one plant, 19 herbivores, 66 parasitoids, 60 predators, five omnivores and three pathogens. There are 370 trophic links between these taxa in the web. The taxa form 82 functionally distinct groups, called trophic species. 2.,Predators consumed significantly more species than did parasitoids: a median of two prey species per species of predator (range = 1,9), compared to a median of one host species per species of parasitoid (range = 1,4). Significant differences in the number of species consumed were also found among the five predator groups: birds (median = 4), spiders (median = 5), Coleoptera (median = 1), Diptera (median = 2) and Hemiptera (median = 7). 3.,Vulnerability, measured by numbers of consumer species, was significantly affected by the herbivores' feeding styles: externally feeding herbivores were most vulnerable and the concealed herbivores were least vulnerable. Miners were vulnerable to the most parasitoid species and externally feeding herbivores were the most vulnerable to predators. 4.,Resource species had a median vulnerability of 13 consumer species, a figure far higher than that in most published food webs. No significant relationship was found between species' vulnerability to predators and vulnerability to parasitoids. However, there was a strong negative relationship between the percentage mortality due to predation and percentage mortality due to parasitism. 5.,The broom food web contains nine orders of insects, a figure higher than previously recorded. The web also contains vertebrates, arachnids, bacteria and fungi. Most of the interactions between the orders were weak. Connectance was calculated for the complete web, the parasitoid sub-web and the predator sub-web. The connectance of the predator sub-web, a value of 0·0364, was more than an order of magnitude larger than the connectance of the entire web (0·0156) or the parasitoid sub-web (0·018). 6.,The body lengths of 52 species in the food web were estimated from field guides or museum specimens. Larger predators consumed smaller prey in 93% of predator,prey interactions. Smaller parasitoids consumed larger hosts in 79% of parasitoid,host interactions. Parasitoids were significantly smaller than predators. 7.,The 52 species were arranged in order of increasing body length along the columns and down the rows of a food web matrix. The predator sub-web was predominantly upper triangular with 8% of non-zero elements falling below the leading diagonal. The parasitoid sub-web was predominantly lower triangular with 21% non-zero elements falling above the leading diagonal. The entire web contains entries both above and below the main diagonal and thus violates a central assumption of the cascade model. [source] Pre-dispersal predation of Taraxacum officinale (dandelion) seedJOURNAL OF ECOLOGY, Issue 2 2005ALOIS HONEK Summary 1Pre-dispersal predation of seeds of Asteraceae has been studied in species where ripening seed is present on plants for long periods but rarely in those where seed maturation is ephemeral and density of consumers is therefore unlikely to keep pace with changes in seed availability. 2We therefore followed predation of dandelion (Taraxacum officinale) seeds by the larvae of Glocianus punctiger and Olibrus bicolor and predicted that both abundance of seed consumers and seed damage will be indirectly proportional to inflorescence availability, and that overall seed damage will be less than in species with longer lived inflorescences. 3We counted the number of dandelion capitula m,2, number of larvae capitulum,1 and percentage of damaged seeds at 10 sites, where the flowering time and densities of dandelions differed. The counts were made in 2002 and 2003, at half-weekly (April,May) or weekly (June,August) intervals. 4Abundance of both species of consumer varied among dandelion patches, and with change in availability of dandelion capitula. Numbers of larvae capitulum,1 were high early and late, when few capitula were available, but decreased at the time of peak flowering when there were many capitula. Production of ready-to-pupate larvae m,2 of a species at a site was similar in successive years, but values for O. bicolor and G. punctiger were not correlated. 5Seed damage paralleled the abundance of consumer larvae, with early and late flowers suffering most. A linear relationship correcting for lost seeds, predicted 30% damage when there were five larvae capitulum,1, below levels reported for species of Asteraceae with persistent inflorescences. 6The intensity of pre-dispersal seed predation is directly proportional to the abundance of seed consumer species and indirectly proportional to the availability of maturing capitula. Consequently, in species with ephemeral, synchronized flowering, where seed is available for only a short time, the majority of plants lose only a small proportion to predators. Although those flowering earlier or later than the peak will suffer a much higher risk, the low overall level of damage is unlikely to influence population biology. [source] | ||||||||||