食饵庇护所对斑块环境下Leslie-Gower捕食系统的影响

建立了一个显式含有空间庇护所的两斑块Leslie-Gower捕食者-食饵系统。假设只有食饵种群在斑块间以常数迁移率迁移,且在每个斑块上食饵间的迁移比局部捕食者-食饵相互作用发生的时间尺度要快。利用两个时间尺度,可以构建用来描述所有斑块总的食饵和捕食者密度的综合系统。数学分析表明,在一定条件下,存在唯一的正平衡点,并且此平衡点全局稳定。进一步,捕食者的数量随着食饵庇护所数量增加而降低;在一定条件下,食饵的数量随着食饵庇护所数量增加先增加后降低,在足够强的庇护所强度下,两物种出现灭绝。对比以往研究,利用显式含有和隐含空间庇护所的数学模型所得结论不一致,这意味着在研究庇护所对捕食系统种群动态影响时,空间结构可能起着重要作用。     

Scaling the effects of predation and disturbance in a patchy environment

The effects of hydraulic disturbances on the impact of two predatory benthic invertebrates on their prey were examined in a stream at two distinct spatial scales. At the scale of small habitat patches (0.0625 m²), hydraulic patch type was an important determinant of the microdistribution of prey and predators. Prey abundances were similar across all patch types at baseflow, but local densities were higher in patches identified as low-flow refugia after periods of high and fluctuating flow. The microdistribution pattern of predatory larvae of a caddisfly, Plectrocnemia conspersa, was similar to that of its prey, whereas predatory larvae of an alderfly, Sialis fuliginosa, did not shift their microdistribution significantly with discharge and were always most abundant in lowflow refugia. There was little evidence of an aggregative response of predators with prey, even though both predators and prey are mobile. Both predator species showed similar patch-specific patterns of per capita consumption rates: uniform consumption rates across hydraulic patch types at low and moderate flows, but highest in flow refugia during high flows. Species-specific patterns, however, were apparent in the magnitude and direction of differences between consumption rates during disturbance events, and in comparable patches at base flow: At high flow, consumption rates for P. conspersa were exaggerated (3.9 times higher) in flow refugia but at par in other patches; for S. fuliginosa they were at par in flow refugia but reduced in other patches (up to 3.3. times lower). These differences may be related to species-specific foraging behaviours (search vs ambush predators) and the influence of prey movements on feeding success. Using the patch-scale results only, it is difficult to predict the effects of physical disturbance on predation intensity at the larger scales of whole habitats, populations or communities. At the large scale (>200 m²), net predator impacts were estimated over the stream reach, using a spatially explicit model that accounts, in an additive way, for habitat heterogeneity and patch-specific responses of predators and prey. The relationship between predator impact over the whole reach and hydraulic disturbance differed for the two predators. The predator impact of S. fuliginosa decreased with increasing hydraulic disturbance, as predicted by the harsh-benign hypothesis. There was no directional trend for P. conspersa, however, and maximum predator impact may occur at intermediate disturbance levels. For the prey community in this stream, predation pressure from S. fuliginosa appears to fluctuate directly with the discharge hydrograph, whereas predation from P. conspersa may be more persistent. Flow refugia may play a dual role in the sructure of stream communities by preventing catastrophic mortality of animals (predators and prey) from physical forces during disturbances, and by maintaining (or perhaps increasing) predation pressure. Summing the effects of species interactions in small habitat patches to the larger scale of a whole stream reach indicates that the scale of approach influences the observed patterns and their implied underlying process.     

Persistence and stability of seed-dispersed species in a patchy environment

A mathematical model is developed for the dynamics of seed-dispersed tree species in a region of forest patches or islands. The relevant variables are the population numbers of individual species populations on each patch. A model that considers only one tree species (of the many present) in a region of N distinct patches is formally analogous to a model of an N-species mutualistic community. Using the theory of M-matrices, which has been successfully applied to mutualistic communities, criteria for persistence and stability of the species are derived. The model is then extended to a community of L species that interact competitively and mutualistically in an N-island region. The possibilities of obtaining numerical parameters for the models are discussed.     

Switching effect of predation on competitive prey species

The fact that the predation pressure has a stabilizing effect on the community of competitive species is demonstrated by a mathematical model of two-preys and one-predator system which has the switching property of predation. By analyzing a dynamical system for these three species populations, it is shown that, in a wide range of parameter space, the system has stable coexisting equilibrium states and the manifold of stable stationary points exhibits a cusp catastrophe and there exist two stable stationary points in the cusp region in the parameter space. Thus, it has been shown that Cause's competitive exclusion is actually relaxed by the switching mechanism of predation.     

Two predators and one prey in a patchy environment: An application of MICMAC modelling

In this paper we apply a new modelling strategy, called MICMAC modelling for studying the possibility of coexistence of two predators, which live in a patchy environment, which feed exclusively on one and the same prey and which do not interact intra- or interspecifically except through this common resource. The MICMAC modelling strategy enables us to model the interaction within each of the patches, the interaction among the patches, and the interaction between these models. The results of the simulations reveal that each of the following factors can cause coexistence by itself or in collaboration with the others: differences in risk of local extinction, dynamical isolation of patches, differences in relative duration of the growth and starvation phase.     

Prey temporarily escape from predation in the presence of a second prey species

1. Indirect interactions between populations of different prey species mediated by a shared predator population are known to affect prey dynamics. 2. Depending on the temporal and spatial scale, these indirect interactions may result in positive (apparent mutualism), neutral or negative effects (apparent competition) of the prey on each other's densities. Although there is ample evidence for the latter, evidence for apparent mutualism is scarce. 3. The effectiveness of using one species of predator for biological control of more than one pest species depends on the occurrence of such positive or negative effects. 4. We used an experimental system consisting of the two prey species Western flower thrips (Franklineilla occidentalis Pergande) and greenhouse whitefly (Trialeurodes vaporariorum Westwood) and a shared predator, the phytoseiid mite Amblyseius swirskii Athias‐Henriot. We released all three species on the same plant and studied their dynamics and distribution along rows of plants. 5. We expected that the more mobile prey species (thrips) would escape temporarily in the presence of the other prey species (whitefly) by dispersing from plants with the predator. The predator was expected to disperse slower in the presence of two prey species because of the higher availability of food. 6. Evidence was found for slower dispersal of predators and short‐term escape of thrips from predation when whiteflies were present, thus confirming the occurrence of short‐term apparent mutualism. 7. The apparent mutualism resulted in a cascade to the first trophic level: a higher proportion of fruits was damaged by thrips in the presence of whiteflies. 8. We conclude that apparent mutualism can be an important phenomenon in population dynamics, and can significantly affect biological control of pest species that share a natural enemy.     

How the aphids got their spots: predation drives self‐organization of aphid colonies in a patchy habitat

Using a 30 day time series of aphid Aphis helianthi and coccinellid counts on 107 mapped racemes of Yucca glauca, we demonstrate progressive, predation‐induced self‐organization of aphid colonies on individual racemes into extremely low and extremely high population sizes. This was driven by a two‐attractor structure of density dependence that developed only in the presence of coccinellid predators. Foraging movements of the coccinellids among plants produced a power law relationship (average power = 0.142) between aphid and coccinellid numbers. This resulted in increased predation pressure on mid‐size colonies and decreased predation pressure on small and large populations. A field‐parameterized mathematical model predicts a two‐attractor structure in broad agreement with our observations. The overall system was integrated by the influence of the largest aphid populations, which determined the total number of coccinellids present, and thus the predation pressure throughout the system. Our study provides clear evidence of predator‐driven self‐organization of prey populations in a patchy environment.     

Antagonistic species interaction drives selection for sex in a predator–prey system

The evolutionary maintenance of sexual reproduction has long challenged biologists as the majority of species reproduce sexually despite inherent costs. Providing a general explanation for the evolutionary success of sex has thus proven difficult and resulted in numerous hypotheses. A leading hypothesis suggests that antagonistic species interaction can generate conditions selecting for increased sex due to the production of rare or novel genotypes that are beneficial for rapid adaptation to recurrent environmental change brought on by antagonism. To test this ecology‐based hypothesis, we conducted experimental evolution in a predator (rotifer)–prey (algal) system by using continuous cultures to track predator–prey dynamics and in situ rates of sex in the prey over time and within replicated experimental populations. Overall, we found that predator‐mediated fluctuating selection for competitive versus defended prey resulted in higher rates of genetic mixing in the prey. More specifically, our results showed that fluctuating population sizes of predator and prey, coupled with a trade‐off in the prey, drove the sort of recurrent environmental change that could provide a benefit to sex in the prey, despite inherent costs. We end with a discussion of potential population genetic mechanisms underlying increased selection for sex in this system, based on our application of a general theoretical framework for measuring the effects of sex over time, and interpreting how these effects can lead to inferences about the conditions selecting for or against sexual reproduction in a system with antagonistic species interaction.     

An epidemic model in a patchy environment

An epidemic model is proposed to describe the dynamics of disease spread among patches due to population dispersal. We establish a threshold above which the disease is uniformly persistent and below which disease-free equilibrium is locally attractive, and globally attractive when both susceptible and infective individuals in each patch have the same dispersal rate. Two examples are given to illustrate that the population dispersal plays an important role for the disease spread. The first one shows that the population dispersal can intensify the disease spread if the reproduction number for one patch is large, and can reduce the disease spread if the reproduction numbers for all patches are suitable and the population dispersal rate is strong. The second example indicates that a population dispersal results in the spread of the disease in all patches, even though the disease can not spread in each isolated patch.     

Seed production and seed predation in a patchy and time-varying environment. Dynamics of a milkweed — tephritid fly system

Summary Vincetoxicum hirundinaria is a longlived perennial herb. Its pod production was measured during seven years in about 40 small isolated patches in two study areas in southeastern Sweden. Total pod production in the two areas varied synchronously and up to about 200 times between years. This variation was mainly due to drought conditions as determined by the interplay of weather (sunshine h) and site characteristics.Populations of a univoltine tephritid fly, euphranta connexa, whose larva feeds on V. hirundinaria seeds in the maturing pods, were monitored for five and seven years in the two study areas respectively. Larval fly populations in the two areas varied 30 and 50-fold between years, with highs in years when pods were abundant and lows when pods were scarce. The percentage of pods attacked by E. connexa, however, varied in the opposite direction, with very high attack rates (about 100%) when pods were scarce and low rates (down to 10–20%) when pods were common. Thus the temporal tracking of food resources by E. connexa was poor, resulting in yearly variations in the amount of unattacked pods (and seeds) being about 2,00-fold.Many host plant patches were small and totally without pods in some years, causing frequent local extinctions of E. connexa. Patches were, however, readily colonized in later years when pods appeared again. Low overall attack rates in certain years were thus only to a minor extent explainable by host plant patches being uncolonized by the fly. The efficient spatial tracking of resources by the fly population allows this population system to be analyzed largely in terms of its temporal dynamics.Although E. connexa populations often exploit only a minor part of their potential larval resources, the rate of population change was closely correlated with these resources expressed on a per capita basis. Natural enemies only have negligible effects on E. connexa population trends. In this population system the herbivore (seed predator) population is thus controlled by its food resources, but weather-imposed temporal variations in resource set are too large for the herbivore population to closely track its resource base. This temporal tracking inertia has important implications for the long-term production of healthy seeds.     

On optimal diet in a patchy environment

Optimal foraging theory has dealt with the following questions independently: (1) On what prey types should an individual predator feed (optimal diet)? (2) How long should a predator stay in each patch if prey is patchily distributed (optimal allocation of time to patches) ? This paper explores optimal foraging in patches containing several different kinds of prey. Results obtained by simulation show that deviations from recent predictions are to be expected, particularly for long interpatch travel times and rapid depletion of profitable prey types. In these situations the tactics of feeding as either specialist or as a generalist can be inferior to a tactic which starts as a specialist and then expands the diet after some time in the patch. Furthermore, predators should not necessarily stay longer in a patch if interpatch travel time increases. Some experimental tests of these new predictions are proposed.     

The Ross-Macdonald model in a patchy environment

We generalize to n patches the Ross-Macdonald model which describes the dynamics of malaria. We incorporate in our model the fact that some patches can be vector free. We assume that the hosts can migrate between patches, but not the vectors. The susceptible and infectious individuals have the same dispersal rate. We compute the basic reproduction ratio R(0). We prove that if R(0)1, then the disease-free equilibrium is globally asymptotically stable. When R(0)>1, we prove that there exists a unique endemic equilibrium, which is globally asymptotically stable on the biological domain minus the disease-free equilibrium.     

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.     

Oscillations in a patchy environment disease model

For a single patch SIRS model with a period of immunity of fixed length, recruitment-death demographics, disease related deaths and mass action incidence, the basic reproduction number R(0) is identified. It is shown that the disease-free equilibrium is globally asymptotically stable if R(0)<1. For R(0)>1, local stability of the endemic equilibrium and Hopf bifurcation analysis about this equilibrium are carried out. Moreover, a practical numerical approach to locate the bifurcation values for a characteristic equation with delay-dependent coefficients is provided. For a two patch SIRS model with travel, it is shown that there are several threshold quantities determining its dynamic behavior and that travel can reduce oscillations in both patches; travel may enhance oscillations in both patches; or travel can switch oscillations from one patch to another.     

Spatial consistency in susceptibility of prey species to predation by two Accipiter hawks

Predators impose strong selection on their prey, regulate prey populations and engage in coevolutionary interactions with their prey. The intensity of selection and the strength of coevolutionary interactions will depend on how stringent predators are in their choice of prey. We estimated susceptibility of different species of birds to predation by two common raptors, the northern goshawk Accipiter gentilis and the Eurasian sparrowhawk A. nisus, in an agricultural landscape in Denmark and boreal forests in Finland. We estimated susceptibility to predation as the deviation of the log₁₀‐transformed observed frequency of prey of different species from the log₁₀‐transformed expectation based on population density during the breeding season. We found a high degree of consistency in susceptibility to predation by the goshawk in two areas in Finland. More importantly, there was significant consistency in susceptibility to predation between Denmark and Finland, albeit the degree of consistency in the goshawk was higher than in the sparrowhawk. There was considerable overlap in susceptibility to predation between goshawk and sparrowhawk in Denmark, but not in Finland, implying differences in intensity of interspecific competition as reflected by a much higher extent of goshawk predation on sparrowhawks in Denmark than in Finland. Our findings suggest that hawks impose similar selection pressures on their prey populations, and that the degree of consistency has implications for intensity of interspecific killing.     

Effects of predation pressure and prey density on short-term indirect interactions between two prey species that share a common predator

1. Generalist predators are important contributors to reliable conservation biological control. Indirect interactions between prey species that share a common generalist predator can influence both community dynamics and the efficacy of biological control. 2. Laboratory cage experiments investigated the impact of the combined consumptive and non-consumptive effects of predation by adult Hippodamia convergens as a shared predator on the population growth and relative abundance of Acyrthosiphon pisum and Aphis gossypii as prey species. Predation pressure and prey density were varied. 3. At low predation pressure the indirect interaction between aphid species was asymmetrical with a proportionally greater negative impact of predation on A. gossypii than on A. pisum. At intermediate predation pressure, the indirect interaction became symmetrical. At high predation pressure and higher levels of prey density, it was asymmetrical with greater negative impact on A. pisum, often driven to local extinction while A. gossypii populations persisted. 4. A linear mixed-effects model including early population growth of both aphid species and predation pressure explained 96% and 92% of the variation in the population growth of A. pisum and A. gossypii, respectively, over an 8-day period. The overall effect of shared predation on the indirect interaction between the two aphid species is best described as apparent commensalism, where A. pisum benefited from early population growth of A. gossypii, while A. gossypii was unaffected by early population growth of A. pisum. Considering these indirect interactions is important for conservation biological control efforts to be successful.     

The dynamics of predation and competition in patchy environments

The model of N. D. Atkinson and B. Shorrocks (J. Anim. Ecol. 50, 461–471 (1981)) as two competing species distributing their progeny amongst patches according to independent negative binomial distributions. The resulting separation of the species increases the likelihood of coexistence. We have assumed a much simpler distribution of the competitors which has enabled us to explore analytically the dynamics of interactions with two competing species and a shared natural enemy in a patchy environment. Two types of natural enemy have been considered: a generalist predator whose dynamics are uncoupled from those of the two prey species, and a specialist (e.g., a parasitoid) whose dynamics are entirely coupled to those of its two prey. The following conclusions emerge. Non-aggregating generalist predators causing random predation across patches are generally destabilizing (although asymmetrical predation may in some case enhance coexistence as a result of preferential predation on the superior competitor). Predator aggregation in patches of high prey density, however, produces a switching effect which tends to promote stability. Coexistence is now even possible with high degrees of correlation in the distribution of the two prey and in situations of extreme competition where the competition coefficients exceed one. The main difference in the models with a specialist parasitoid as the natural enemy is a reduction in stability compared with the equivalent generalist-prey interaction. But stable coexistence can still readily occur if the natural enemies aggregate markedly in patches of high prey density.     

Size-dependent predation risk in cryptic prey

Journal of Ethology - Visual crypsis of prey is determined by the interaction between an individual’s physical appearance to their predators and visual aspects of their environment. Physical...     

Allee effect makes possible patchy invasion in a predator–prey system

The dynamics of interacting ecological populations results from the interplay between various deterministic and stochastic factors and this is particularly the case for the phenomenon of biological invasion. Whereas the spread of invasive species via propagation of a population front was shown to appear as a result of deterministic processes, the spread via formation, interaction and movement of separate patches has been recently attributed to the influence of environmental stochasticity. An appropriate understanding of the comparative importance of deterministic and stochastic mechanisms is still lacking, however. In this paper, we show that the patchy invasion appears to be possible also in a fully deterministic predator–prey model as a result of the Allee effect.