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Herbivore Population Dynamics (herbivore + population_dynamics)
Selected AbstractsEffects of nitrogen deposition on the interaction between an aphid and its host plantECOLOGICAL ENTOMOLOGY, Issue 1 2008CARALYN B. ZEHNDER Abstract 1.,Anthropogenic increases in nitrogen deposition are impacting terrestrial ecosystems worldwide. While some of the direct ecosystem-level effects of nitrogen deposition are understood, the effects of nitrogen deposition on plant,insect interactions and on herbivore population dynamics have received less attention. 2.,Nitrogen deposition will potentially influence both plant resource availability and herbivore population growth. If increases in herbivore population growth outstrip increases in resource availability, then increases in the strength of density dependence expressed within the herbivore population would be predicted. Alternatively, if plant resources respond more vigorously to nitrogen deposition than do herbivore populations, a decline in the strength of density dependence would be expected. No change in the strength of density dependence acting upon the herbivore population would suggest equivalent responses by herbivores and plants. 3.,A density manipulation experiment was performed to examine the effect of nitrogen deposition on the interaction between a host plant, Asclepias tuberosa, and its herbivore, Aphis nerii. Aphid maximum per capita growth rate (Rmax), carrying capacity (K), and the strength of density dependence were measured under three nitrogen deposition treatments. The effect of nitrogen deposition on the relationship among these three measures of insect population dynamics was explored. 4.,Simulated nitrogen deposition increased aphid per capita population growth, plant foliar nitrogen concentrations, and plant biomass. Nitrogen deposition caused Rmax and K to increase proportionally, leading to no overall change in the strength of density dependence. In this system, potential changes in the negative feedback processes operating on herbivore populations following nitrogen deposition appear to be buffered by concomitant changes in resource availability. [source] Predator disease out-break modulates top-down, bottom-up and climatic effects on herbivore population dynamicsECOLOGY LETTERS, Issue 4 2006Christopher C. Wilmers Abstract Human-introduced disease and climatic change are increasingly perturbing natural ecosystems worldwide, but scientists know very little about how they interact to affect ecological dynamics. An outbreak of canine parvovirus (CPV) in the wolf population on Isle Royale allowed us to test the transient effects of an introduced pathogen and global climatic variation on the dynamics of a three-level food chain. Following the introduction of CPV, wolf numbers plummeted, precipitating a switch from top-down to bottom-up regulation of the moose population; consequently, the influence of climate on moose population growth rate doubled. This demonstrates that synergistic interactions between pathogens and climate can lead to shifts in trophic control, and suggests that predators in this system may play an important role in dampening the effects of climate change on the dynamics of their prey. [source] Individual growth rates do not predict aphid population densities under altered atmospheric conditionsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2010Edward B. Mondor 1Altered atmospheric composition, associated with climate change, can modify herbivore population dynamics through CO2 and/or O3 -mediated changes in plant quality. 2Although pea aphid Acyrthosiphon pisum genotypes exhibit intraspecific variation in population growth in response to atmospheric composition, the proximate mechanisms underlying this variation are largely unknown. 3By rearing single (green, pink) and mixed (green + pink) pea aphid genotypes on red clover Trifolium pratense at the Aspen Free Air CO2 and O3 Enrichment (Aspen FACE) site, we assessed whether: (i) elevated CO2 and/or O3 concentrations alter aphid growth and development and (ii) individual aphid growth rates predict aphid population densities. 4We showed that growth and development of individual green and pink aphids were not influenced by CO2 and/or O3 concentrations when reared as individual or mixed genotypes. Individual growth rates, however, did not predict population densities. 5Reared as a single genotype, green pea aphid populations decreased in response to elevated CO2 concentrations, but not in response to elevated CO2 + O3 concentrations. Pink pea aphid populations reared as a single genotype were unaffected by augmented CO2 or O3. Populations of mixed genotypes, however, were reduced under elevated CO2 concentrations, irrespective of O3 concentrations. 6Herbivore population sizes may not readily be predicted from growth rates of individual organisms under atmospheric conditions associated with global climate change. [source] Influence of plant quality on pine sawfly population dynamicsOIKOS, Issue 3 2000Stig Larsson The contribution of plant quality to the population dynamics of herbivorous insects has been an issue of much controversy. Many studies have documented how variable plant quality differentially influences the survival and fecundity of insect individuals. Whether or not such effects can be translated to the level of insect populations is, however, not clear. In order to test this hypothesis one needs to combine processes at both the level of the individual and the population. This is difficult with an empirical approach, but could be achieved by means of modeling given that appropriate data exist for both levels of organization. In this paper we report on a model developed to analyze whether altered Scots pine (Pinus sylvestris) quality can contribute to the build-up of populations of the European pine sawfly (Neodiprion sertifer). Experimental data on responses of sawfly larvae to variable plant quality, i.e. needle concentrations of resin acids, were used to parameterize the model. Larval survival and sawfly fecundity are reduced at high resin acid concentrations. However, high resin acid concentrations are, at the same time, beneficial because larval defense against predators is enhanced. In the model, data on individual responses were combined with literature data at the population level; a type III functional response related to cocoon predation was presumed to be the density-dependent process regulating sawfly populations. The analysis showed that the risk for an outbreak is high when needle resin acid concentration (r) or larval predation pressure (p) is low. When r or p is high there is no risk. By analyzing different scenarios it was found that small changes in r and p can result in the sawfly population moving from low to high outbreak risk. Changes of the same, or larger, magnitude in r have been observed in empirical studies. The role of tritrophic interactions was also considered. This was done by removing the positive effects of resin acids on larval performance in the model. It was found that the anti-predator defense of N.sertifer makes it prone to outbreak under wider combinations of r and p than an insect without the defense. We conclude that small changes in a density-independent factor, such as needle chemistry, can have significant effects on herbivore population dynamics because increased fecundity and survival caused by needle quality may allow the population to escape the control of density-dependent factors, such as cocoon predation. [source] | ||||||||||