Predator-free Space Research Articles

Predation and Climate Limit Establishment Success of the Kyushu Strain of the Biological Control Agent Aphalara itadori (Hemiptera: Aphalaridae) in the Northeastern United States.

Species of knotweeds, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), including Japanese knotweed (R. japonica Houtt.), are among the most invasive and ecologically destructive plant species introduced to North America and Europe. The Kyushu strain of the psyllid Aphalara itadori Shinji (Hemiptera: Aphalaridae) has been approved as a biological control agent for release against Japanese knotweed in the United Kingdom, Canada, and the United States. However, recent reports from Canada suggest that both biotic and abiotic factors may limit its establishment. Therefore, we examined the potential role of predation by comparing open- versus closed-sleeve treatments, and climate mis-matches by collecting temperature data from release sites and performing climate suitability analyses using MaxEnt. Our results indicated that populations of the Kyushu strain could only be maintained in the field in closed-sleeve treatments, suggesting that predation is likely limiting the establishment success of this strain. In addition, we noted that daily maximum temperatures at our field sites might exceed documented developmental thresholds for this strain, and that MaxEnt species distribution modeling indicates no climate similarities between locations in eastern North America and Kyushu. Combined with previous results, our study suggests that the establishment of the Kyushu strain of A. itadori as a biological control agent for Japanese knotweed may be limited in eastern North America. We suggest that one strategy to increase the probability of establishment of the Kyushu strain could be to increase the number of release sites in an effort to find a more optimal niche with predator-free space.

Natural History and Parasitoids of Arawacus ellida (Lycaenidae: Eumaeini) in Brazil

We report the life history from egg to adult of the lycaenid butterfly Arawacus ellida on the leaves of Solanum paniculatum L. (Solanaceae) in Alagoas, Brazil. Of four caterpillars sampled from S. paniculatum, one was parasitized by a Braconidae and one by a Chalcididae. We summarize published and unpublished life history records for A. ellida. Besides Solanaceae, this species eats Asteraceae. The significance of this paper is that it provides the background information needed to determine whether the use of Solanaceae and Asteraceae provides the caterpillars with predator-free space.

A subterranean adaptive radiation of amphipods in Europe

Adaptive radiations are bursts of evolutionary species diversification that have contributed to much of the species diversity on Earth. An exception is modern Europe, where descendants of ancient adaptive radiations went extinct, and extant adaptive radiations are small, recent and narrowly confined. However, not all legacy of old radiations has been lost. Subterranean environments, which are dark and food-deprived, yet buffered from climate change, have preserved ancient lineages. Here we provide evidence of an entirely subterranean adaptive radiation of the amphipod genus Niphargus, counting hundreds of species. Our modelling of lineage diversification and evolution of morphological and ecological traits using a time-calibrated multilocus phylogeny suggests a major adaptive radiation, comprised of multiple subordinate adaptive radiations. Their spatio-temporal origin coincides with the uplift of carbonate massifs in South-Eastern Europe 15 million years ago. Emerging subterranean environments likely provided unoccupied, predator-free space, constituting ecological opportunity, a key trigger of adaptive radiation. This discovery sheds new light on the biodiversity of Europe.

Warning signals promote morphological diversification in fossorial uropeltid snakes (Squamata: Uropeltidae)

AbstractMany species possess warning colourations that signal unprofitability to predators. Warning colourations are also thought to provide prey with a ‘predator-free space’ and promote niche expansion. However, how such strategies release a species from environmental constraints and facilitate niche expansion is not clearly understood. Fossoriality in reptiles imposes several morphological limits on head and body size to facilitate burrowing underground, but many fossorial snakes live close to the surface and occasionally move above ground, exposing them to predators. In such cases, evolving antipredator defences that reduce predation on the surface could potentially relax the morphological constraints associated with fossoriality and promote morphological diversification. Fossorial uropeltid snakes possess varying degrees of conspicuous warning colourations that reduce avian predation when active above ground. We predicted that species with more conspicuous colourations will exhibit more robust body forms and show faster rates of morphological evolution because constraints imposed by fossoriality are relaxed. Using a comparative phylogenetic approach on the genus Uropeltis, we show that more conspicuous species tend to have more robust morphologies and have faster rates of head-shape evolution. Overall, we find that the evolution of warning colourations in Uropeltis can facilitate niche expansion by influencing rates of morphological diversification.

Combined effects of predator cues and competition define habitat choice and food consumption of amphipod mesograzers

Predation has direct impact on prey populations by reducing prey abundance. In addition, predator presence alone can also have non-consumptive effects on prey species, potentially influencing their interspecific interactions and thus the structure of entire assemblages. The performance of potential prey species may, therefore, depend on both the presence of predators and competitors. We studied habitat use and food consumption of a marine mesograzer, the amphipod Echinogammarus marinus, in the presence/absence of a fish mesopredator and/or an amphipod competitor. The presence of the predator affected both habitat choice and food consumption of the grazer, indicating a trade-off between the use of predator-free space and food acquisition. Without the predator, E. marinus were distributed equally over different microhabitats, whereas in the presence of the predator, most individuals chose a sheltered microhabitat and reduced their food consumption. Furthermore, habitat choice of the amphipods changed in the presence of interspecific competitors, also resulting in reduced feeding rates. The performance of E. marinus is apparently driven by trait-mediated direct and indirect effects caused by the interplay of predator avoidance and competition. This highlights the importance of potential non-consumptive impacts of predators on their prey organisms. The flexible responses of small invertebrate consumers to the combined effects of predation and competition potentially lead to changes in the structure of coastal ecosystems and the multiple species interactions therein.

The flexible lek:Phymatopus hectathe gold swift demonstrates the evolution of leking and male swarming via a hotspot (Lepidoptera: Hepialidae)

Leking moths present an evolutionary problem in their apparently simultaneous reversal of male–female attraction. The mating system of Phymatopus (or Hepialus) hecta embraces an unusually wide range of procedures. Both males and females use medium-range olfactory attractants (also probably visual signals), and both sexes will lure, and both will approach, the other, either when flying or perched. This produces an ‘infinite variety’ which includes the classic moth mating procedure (males fly to sessile female); a typical lek procedure (female flies to sessile male); a mating swarm (hovering male follows passing female); and intermediates such as a mutual courtship dance. Male behaviour includes a flying display, two sessile displays, and an escalating war of attrition. The system is versatile, persistent, and probably evolutionarily stable. The lek site has a high density of perches suitable for copulation which facilitate predator-escape by means of a dead drop. The whole supports a model for the evolution of resource-based leks which commence with a concentration of females on a hotspot, leading to a concentration of males; and then an escalating process of sexual selection as males become increasingly attractive over a distance to females, and females use the males as a way of locating the resource. The main stabilizing pressure may be selection for efficient mate acquisition, and as with grouse leking systems, the precondition for evolution was probably having travelling females that actively sought a reproductive resource or a predator free space. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 184–201.

Synthesis of the conservation value of the early-successional stage in forests of eastern North America

As a result of changes in natural and anthropogenic disturbance regimes, the extent of early-successional forest across much of eastern North American is near historic lows, and continues to decline. This has caused many scientists to identify the conservation of early-successional species as a high priority. In this synthesis, we discuss the conservation implications of this loss of early-successional habitats using examples from the literature on songbirds. Early-successional “shrubland” bird species require conditions and resources present in recently disturbed sites. These conditions are ephemeral and change rapidly over time as sites become dominated by later-seral species. Historical disturbance regimes such as wind-throw, fire and flooding have been altered or suppressed in eastern forests through human activity such as conversion of forests to younger aged stands more resistant to wind, fire suppression and mesophication of fire-adapted communities, and suppression of beaver activity and flooding. Furthermore, anthropogenic disturbance has shifted over much of the region to types of land use that provide less shrubland habitat of lower quality than historically. Despite scientific evidence in support of this concern, there is still misunderstanding about the role of disturbance in maintaining biodiversity, and public opposition to management remains a challenge to conserving these communities. Contemporary approaches use natural disturbance regimes to inform management practices that employ historical agents where possible or surrogates when necessary to achieve desired future conditions defined on the basis of regional population or community status. Conservation of early-successional communities occurs within the context of other potentially conflicting ecological values, such as the conservation and enhancement of biologically mature forest. Recent findings, however, show shrubland habitat can augment diversity in forested landscapes by providing seasonal resources for mature-forest species, such as food or predator-free space for juvenile forest songbirds that seek out early-successional habitats during the transition to independence. Balancing the conservation of early-successional shrubland species with other, sometimes conflicting values is an active area of current conservation research. In some cases the conservation of shrubland birds can be coordinated with commercial activities like silviculture or maintenance of infrastructure (e.g. powerline corridors), although our work indicates that deliberate efforts expressly directed at conservation of early-successional shrubland species are more effective.

Joint estimation of habitat dynamics and species interactions: disturbance reduces co‐occurrence of non‐native predators with an endangered toad

1. Ecologists have long been interested in the processes that determine patterns of species occurrence and co-occurrence. Potential short-comings of many existing empirical approaches that address these questions include a reliance on patterns of occurrence at a single time point, failure to account properly for imperfect detection and treating the environment as a static variable. 2. We fit detection and non-detection data collected from repeat visits using a dynamic site occupancy model that simultaneously accounts for the temporal dynamics of a focal prey species, its predators and its habitat. Our objective was to determine how disturbance and species interactions affect the co-occurrence probabilities of an endangered toad and recently introduced non-native predators in stream breeding habitats. For this, we determined statistical support for alternative processes that could affect co-occurrence frequency in the system. 3. We collected occurrence data at stream segments in two watersheds where streams were largely ephemeral and one watershed dominated by perennial streams. Co-occurrence probabilities of toads with non-native predators were related to disturbance frequency, with low co-occurrence in the ephemeral watershed and high co-occurrence in the perennial watershed. This occurred because once predators were established at a site, they were rarely lost from the site except in cases when the site dried out. Once dry sites became suitable again, toads colonized them much more rapidly than predators, creating a period of predator-free space. 4. We attribute the dynamics to a storage effect, where toads persisting outside the stream environment during periods of drought rapidly colonized sites when they become suitable again. Our results support that even in highly connected stream networks, temporal disturbance can structure frequencies with which breeding amphibians encounter non-native predators. 5. Dynamic multi-state occupancy models are a powerful tool for rigorously examining hypotheses about inter-species and species-habitat interactions. In contrast to previous methods that infer dynamic processes based on static patterns in occupancy, the approach we took allows the dynamic processes that determine species-species and species-habitat interactions to be directly estimated.

The Effect of Structural Complexity, Prey Density, and “Predator-Free Space” on Prey Survivorship at Created Oyster Reef Mesocosms

Interactions between predators and their prey are influenced by the habitat they occupy. Using created oyster (Crassostrea virginica) reef mesocosms, we conducted a series of laboratory experiments that created structure and manipulated complexity as well as prey density and “predator-free space” to examine the relationship between structural complexity and prey survivorship. Specifically, volume and spatial arrangement of oysters as well as prey density were manipulated, and the survivorship of prey (grass shrimp, Palaemonetes pugio) in the presence of a predator (wild red drum, Sciaenops ocellatus) was quantified. We found that the presence of structure increased prey survivorship, and that increasing complexity of this structure further increased survivorship, but only to a point. This agrees with the theory that structural complexity may influence predator-prey dynamics, but that a threshold exists with diminishing returns. These results held true even when prey density was scaled to structural complexity, or the amount of “predator-free space” was manipulated within our created reef mesocosms. The presence of structure and its complexity (oyster shell volume) were more important in facilitating prey survivorship than perceived refugia or density-dependent prey effects. A more accurate indicator of refugia might require “predator-free space” measures that also account for the available area within the structure itself (i.e., volume) and not just on the surface of a structure. Creating experiments that better mimic natural conditions and test a wider range of “predator-free space” are suggested to better understand the role of structural complexity in oyster reefs and other complex habitats.

Predator Effects in Predator-Free Space: the Remote Effects of Predators on Prey

Predators can have effects on prey populations that are connected by migration (i.e. prey metapopulations) because predator-mediated changes in prey behavior and abundance effectively transmit the impact of predators into predator-free prey populations. Behavioral changes in prey that might give rise to effects are altered rates of migration or activity in the presence of predation risk (called non-consumptive effects, fear- or µ-driven effects, and risk effects). Changes in prey abundance that may result in effects arise from changes in prey density due to direct predation (i.e. consumptive effects, also called N-driven effects and predation effects). Remote effects provide a different perspective on both predator-prey interactions and spatial subsidies, illustrating how the interplay among space, time, behavior, and consumption generates emergent spatial dynamics in places where we might not expect them. We describe how strong effects of predators may essentially generate remote control over the dynamics of local populations, alter the persistence of metapopulations, shift the importance of particular paradigms of metacommunity structure, alter spatial subsidies, and affect evolutionary dynamics. We suggest how experiments might document effects and predict that effects will be an important component of prey dynamics under several common scenarios: when predators induce large changes in prey dispersal behavior, when predators dramatically reduce the number of prey available to disperse, when prey movement dynamics occur over greater distances or shorter timescales than predator movement, and when prey abundance is not already limited by competitors or conspecifics.

Compartmentalization of the soil animal food web as indicated by dual analysis of stable isotope ratios ( 15N/ 14N and 13C/ 12C)

The soil animal food web has become a focus of recent ecological research but trophic relationships still remain enigmatic for many taxa. Analysis of stable isotope ratios of N and C provides a powerful tool for disentangling food web structure. In this study, animals, roots, soil and litter material from a temperate deciduous forest were analysed. The combined measurement of δ 15N and δ 13C provided insights into the compartmentalization of the soil animal food web. Leaf litter feeders were separated from animals relying mainly on recent belowground carbon resources and from animals feeding on older carbon. The trophic pathway of leaf litter-feeding species appears to be a dead end, presumably because leaf litter feeders (mainly diplopods and oribatid mites) are unavailable to predators due to large size and/or strong sclerotization. Endogeic earthworms that rely on older carbon also appear to exist in predator-free space. The data suggest that the largest trophic compartment constitutes of ectomycorrhizal feeders and their predators. Additionally, there is a smaller trophic compartment consisting of predators likely feeding on enchytraeids and potentially nematodes.

Spatiotemporal within-plant distribution of the spider miteTetranychus urticaeand associated specialist and generalist predators

Predators are important determinants of the spatiotemporal distribution of prey within a given habitat. The predator effects may vary with diet specialisation, the associated risk posed to prey and, if multiple predators are present, the predator-predator interactions. We examined the spatiotemporal distribution of the herbivorous spider mite Tetranychus urticae and the associated specialist and generalist predators Phytoseiulus persimilis and Neoseiulus californicus on bean plants. Tetranychus urticae is a key pest on numerous agricultural crops. Both predators are used singly and in combination for biological control of spider mites. Population development and within-plant distribution of the spider mites and the predators were compared among five treatments: T. urticae without predators, with either predator alone and with both predators in combination at full and half densities. The spider mites were suppressed to zero density in both predator combination treatments but not in the single predator treatments. The predators determined the spatiotemporal distribution of the spider mites through density- and behaviour-mediated effects, and these effects were linked to diet specialisation. The specialist P. persimilis exerted stronger density-mediated effects on the spider mite distribution than did the generalist N. californicus. Either predator induced in the spider mites early upward migration on plants. The predators also affected each other's distribution. The aggregation level of N. californicus was lowered by P. persimilis but not vice versa. In combination, the predators were more dispersed than when alone, reducing the predator-free space and leading to the local extinction of T. urticae.

Behavioral Indicators of Predator space use: Studying Species Interactions through the behavior of Predators

Predation has major impacts on survival and reproductive success for many species. To quantify these effects, ecologists often choose to intensively study prey populations to measure predation rates and/or estimate predator abundance. But in some cases, predation rates are less strongly related to predator abundance per se than to spatial and temporal patterns of predator space use; thus, quantifying the latter may provide meaningful surrogates of predation rates that scale up to larger areas. This is particularly true when safety for prey, especially sessile and vulnerable prey, is strongly linked to predator-free space. Our own research programs have used two general types of behavioral indicators to quantify space use by predators: giving-up densities, as a surrogate for patch quitting harvest rates, and activity density. We discuss two general mechanisms by which predator-free (or predator-poor) space is created and link these mechanisms to behavioral indicators that can be easily collected in the fie...

Spatial heterogeneity in predator activity, nest survivorship, and nest-site selection in two forest thrushes

The ability of prey to find and use predator-free space has far-reaching consequences for their persistence and interactions with their predators. We tested whether nest survivorship of the ground-nesting veery (Catharus fuscescens) and shrub-nesting wood thrush (Hylocichla mustelina) was related to the local absence of a major nest predator, the white-footed mouse (Peromyscus leucopus). Mouse-free space was defined by trap stations that failed to trap a mouse during the avian breeding season (approximately May through July). In addition, mouse activity was quantified at individual trap stations based on the number of captures during the same period (six 2.25-ha trapping grids, each containing 121 trap stations trapped repeatedly throughout the summer between 1998 and 2002.) Annual mouse-free space was correlated with other measures of mouse activity based on trapping data. Both mouse-free space and activity metrics were significantly related to annual rates of nest predation (i.e., nest daily mortality rate) in veery but not wood thrush. Likewise, mouse-free space and mouse activity within the nest neighborhood (approximately 30x30 m2 surrounding each nest) was significantly related to nest survivorship in veery but not wood thrush. More trap stations had consistently greater (hotspots) and lesser (coldspots) mouse activity than expected by chance, and veeries were significantly more likely to nest near stations that had below the grid-average trapping success. Our study thus documented significant spatial variability in predator activity and its relationship to nest predation and nest-site selection in a ground-nesting songbird.

Ecosystem Engineering across Environmental Gradients: Implications for Conservation and Management

Ecosystem engineers are organisms whose presence or activity alters their physical surroundings or changes the flow of resources, thereby creating or modifying habitats. Because ecosystem engineers affect communities through environmentally mediated interactions, their impact and importance are likely to shift across environmental stress gradients. We hypothesize that in extreme physical environments, ecosystem engineers that ameliorate physical stress are essential for ecosystem function, whereas in physically benign environments where competitor and consumer pressure is typically high, engineers support ecosystem processes by providing competitor- or predator-free space. Important ecosystem engineers alleviate limiting abiotic and biotic stresses, expanding distributional limits for numerous species, and often form the foundation for community development. Because managing important engineers can protect numerous associated species and functions, we advocate using these organisms as conservation targets, harnessing the benefits of ecosystem engineers in various environments. Developing a predictive understanding of engineering across environmental gradients is important for furthering our conceptual understanding of ecosystem structure and function, and could aid in directing limited management resources to critical ecosystem engineers.