Stability Of Predator Research Articles

The Combined Effects of Warming and Body Size on the Stability of Predator-Prey Interactions

Environmental temperature and body size are two prominent drivers of predation. Despite the ample evidence of their independent effects, the combined impact of temperature and predator-prey body size ratio on the strength and stability of trophic interactions is not fully understood. We experimentally tested how water temperature alters the functional response and population stability of dragonfly nymphs (Cordulegaster boltonii) feeding on freshwater amphipods (Gammarus pulex) across a gradient of their body size ratios. Attack coefficients were highest for small predators feeding on small prey at low temperatures, but shifted toward the largest predators feeding on larger prey in warmer environments. Handling time appeared to decrease with increasing predator and prey body size in the cold environment, but increase at higher temperatures. These findings indicate interactive effects of temperature and body size on functional responses. There was also a negative effect of warming on the stability of predator and prey populations, but this was counteracted by a larger predator-prey body size ratio at higher temperatures. Here, a greater Hill exponent reduced feeding at low prey densities when predators were much larger than their prey, enhancing the persistence of both predator and prey populations in the warmer environment. These experimental findings provide new mechanistic insights into the destabilizing effect of warming on trophic interactions and the key role of predator-prey body size ratios in mitigating these effects.

Prediction of changing predator–prey interactions under warming: A simulation study using two aphid–ladybird systems

AbstractPredator–prey interactions are key factors for understanding ecosystem structure and function. Global warming alters the dynamics and stability of predator and prey populations in the long term. Extreme temperatures can also lead to short‐term population outbreaks and collapses. Thus, it is necessary to consider time scales when predicting warming effects on predator–prey interactions. Two aphid–ladybird systems, Myzus persicae–Coccinella septempunctata (M‐C) and Aphis gossypii–C. septempunctata (A‐C), were investigated. Using a temperature‐dependent predator–prey model, the short‐ (SIS, daily interactions) and long‐term interaction strength (LIS, interactions after reaching a persistent state) were quantified under different temperatures based on a dynamic index. SIS and LIS increased with temperature, but the patterns and magnitudes of the two systems differed. SIS increased linearly and exponentially in the A‐C and M‐C system, respectively. However, the SISs in the A‐C system were stronger than those in the M‐C system under most temperature ranges. LIS increased linearly with temperature in both systems; its values in the M‐C system were always larger than those in the A‐C system. The abruptly increasing SIS in the M‐C system caused population collapse, which was the main reason for the magnitude reversal between the SISs and LISs of the two systems. The A‐C system did not collapse, but a decoupled SIS and subsequent aphid outbreak were temporarily observed under extreme temperatures. Understanding how time scales influence interaction strengths may be critical to predicting population stability and fluctuations in ecosystems.

Trophic selectivity in aquatic isopods increases with the availability of resources

Abstract Trophic selectivity has major influences on consumers’ fitness, stability of predator and prey populations, and nutrient fluxes in food webs. Trophic selectivity occurs when the relative abundances of resources in a consumer's diet differ from their relative abundances in the environment. This discrepancy between resources abundance and use has been predicted to increase with the availability of resources in the environment. Trophic selectivity has also been predicted to increase with the heterogeneity of resources quality in the environment. Despite their ecological and evolutionary implications, conclusive in situ tests of these predictions are still lacking. We challenged these two predictions by studying 15 closely related species of isopods distributed along a wide range of resource availability (RA) (from 1.3 to 57.6 g of organic carbon per m2). The dataset ranged from deep cave systems, considered as some of the most resource‐limited environments on Earth, to highly productive surface streams. For each species, we quantified the relative abundance of all available resources in the environment and estimated the heterogeneity in the stoichiometric quality of these resources. Isopod diet was determined using C and N stable isotopes and a Bayesian mixing model. The degree of trophic selectivity was then calculated for each species. By coupling a standardized quantification of trophic resources with a fine determination of diets using stable isotopes, we uncovered a positive relationship between RA and trophic selectivity. In contrast to our second prediction, trophic selectivity did not correlate with the heterogeneity of resources quality. Our results have important implications in trophic ecology by highlighting that RA was a main driver of trophic choices in aquatic invertebrates across a broad range of environments. These findings call for further evaluation of the mechanisms (e.g. trophic competition) causing the positive relationship between trophic selectivity and RA, as these mechanisms could be closely linked to those generating the documented relationship between species richness and productive energy. A free Plain Language Summary can be found within the Supporting Information of this article.

Ecological Responses to Habitat Fragmentation Per Se

For this article, I reviewed empirical studies finding significant ecological responses to habitat fragmentation per se—in other words, significant responses to fragmentation independent of the effects of habitat amount (hereafter referred to as habitat fragmentation). I asked these two questions: Are most significant responses to habitat fragmentation negative or positive? And do particular attributes of species or landscapes lead to a predominance of negative or positive significant responses? I found 118 studies reporting 381 significant responses to habitat fragmentation independent of habitat amount. Of these responses, 76% were positive. Most significant fragmentation effects were positive, irrespective of how the authors controlled for habitat amount, the measure of fragmentation, the taxonomic group, the type of response variable, or the degree of specialization or conservation status of the species or species group. No support was found for predictions that most significant responses to fragmentation should be negative in the tropics, for species with larger movement ranges, or when habitat amount is low; most significant fragmentation effects were positive in all of these cases. Thus, although 24% of significant responses to habitat fragmentation were negative, I found no conditions in which most responses were negative. Authors suggest a wide range of possible explanations for significant positive responses to habitat fragmentation: increased functional connectivity, habitat diversity, positive edge effects, stability of predator–prey/host–parasitoid systems, reduced competition, spreading of risk, and landscape complementation. A consistent preponderance of positive significant responses to fragmentation implies that there is no justification for assigning lower conservation value to a small patch than to an equivalent area within a large patch—instead, it implies just the opposite. This finding also suggests that land sharing will usually provide higher ecological value than land sparing.

Hopf bifurcation and stability in predator–prey model with a stage-structure for prey

A predator–prey system with B–D functional response and stage-structure for prey is presented. In the (d-τ) plane, the regions of stability and Hopf bifurcation are found by analyzing the associated characteristic transcendental equation. Further, global stability of equilibria are studied by using comparison theorem. Some numerical simulations are also given to illustrate our results.

Behavioral states of predators stabilize predator–prey dynamics

This study considers a common community model (i.e., Rosenzweig–MacArthur model) with an explicit consideration of the behavioral states of predators. Following a mechanistic interpretation of the functional response model in the model, a fraction of predator individuals are assumed searching for prey while the rest are assumed handling prey at any given time. How the explicit consideration of the behavioral states affects the model dynamics with respect to environmental enrichment is considered. The analysis shows that the explicit consideration of the behavioral states can substantially increase the stability of predator–prey dynamics.

Complementary predation on metamorphosing species promotes stability in predator–prey systems

Functionally redundant predation and functionally complementary predation are both widespread phenomena in nature. Functional complementary predation can be found, for example, when predators feed on different life stages of their prey, while functional redundant predation occurs when different predators feed on all life stages of a shared prey. Both phenomena are common in nature, and the extent of differential life-stage predation depends mostly on prey life history; complementary predation is expected to be more common on metamorphosing prey species, while redundant predation is thought to be higher on non-metamorphosing species. We used an ordinary differential equation model to explore the effect of varying degree of complementary and redundant predation on the dynamic properties of a system with two predators that feed on an age-structured prey. Our main finding was that predation on one stage (adult or juvenile) resulted in a more stable system (i.e., it is stable for a wider range of parameters) compared to when the two predators mix the two prey developmental stages in their diet. Our results demonstrate that predator–prey dynamics depends strongly on predators' functionality when predator species richness is fixed. Results also suggest that systems with metamorphosing prey are expected to be more diverse compared to systems with non-metamorphosing prey.

INTERACTION OF TOP-DOWN AND BOTTOM-UP LIFE HISTORY TRADE-OFFS IN MOOSE (ALCES ALCES)

Moose (Alces alces) in south-central Alaska have been found to have phenotypic life history trade-offs that can be partitioned into the same “bottom-up” and “top- down” trophic framework often applied at the population level. The potential interaction of these life history trade-offs was studied under varying degrees of predation and nutritional limitation using models based on data from radio-collared moose in south-central Alaska. The interaction was mildly antiregulatory, assuming that bottom-up trade-offs are density dependent. That is, as nutritional constraints increased, a female that skipped reproduction after successfully rearing a calf enhanced the survival of herself and her yearling enough in the second year to overcompensate for the loss of productivity. In a declining population, the reverse could occur, accentuating the decline. A more general, stage projection matrix was used to model a broader range of predation rates in summer and winter, in order to contrast the potential importance of bears (Ursus arctos and U. americanus) and wolves (Canis lupus) in such an interaction. The greatest effect of life history interactions on population growth occurred with moderate predation in summer and heavy predation in winter. Relative to direct ecological effects on survival and reproduction, the influence of such an interaction was relatively weak. However, subtle effects on the stability of predator– prey interactions, particularly those involving bear predation, cannot be excluded because of the antiregulatory nature of the interaction and uncertainties about class-specific vulnerability to predation in other settings. These findings underscore the relevance of understanding the alternative life history choices that arise from interactions in both directions on the food chain, particularly given that the top-down trade-offs are usually poorly known.