Camouflage in predators

Camouflage – adaptations that prevent detection and/or recognition – is a key example of evolution by natural selection, making it a primary focus in evolutionary ecology and animal behaviour. Most work has focused on camouflage as an anti‐predator adaptation. However, predators also display specific colours, patterns and behaviours that reduce visual detection or recognition to facilitate predation. To date, very little attention has been given to predatory camouflage strategies. Although many of the same principles of camouflage studied in prey translate to predators, differences between the two groups (in motility, relative size, and control over the time and place of predation attempts) may alter selection pressures for certain visual and behavioural traits. This makes many predatory camouflage techniques unique and rarely documented. Recently, new technologies have emerged that provide a greater opportunity to carry out research on natural predator–prey interactions. Here we review work on the camouflage strategies used by pursuit and ambush predators to evade detection and recognition by prey, as well as looking at how work on prey camouflage can be applied to predators in order to understand how and why specific predatory camouflage strategies may have evolved. We highlight that a shift is needed in camouflage research focus, as this field has comparatively neglected camouflage in predators, and offer suggestions for future work that would help to improve our understanding of camouflage.     

Detecting predator–prey relationships in the sea

Understanding the strength and diversity of predator‐prey interactions among species is essential to understand ecosystem consequences of population‐level variation. Directly quantifying the predatory behaviour of wild fishes at large spatial scales (>100 m) in the open sea is fraught with difficulties. To date the only empirical approach has been to search for correlations in the abundance of predators and their putative prey. As an example we use this approach to search for predators of the keystone crown‐of‐thorns starfish. We show that this approach is unlikely to detect predator–prey linkages because the theoretical relationship is non‐linear, resulting in multiple possible prey responses for single given predator abundance. Instead we suggest some indication of the strength and ecosystem importance of a predator–prey relationship can be gained by using the abundance of both predators and their putative prey to parameterize functional response models.     

Predation and searching efficiency of a ladybird beetle, Coccinella septempunctata Linnaeus in laboratory environment

The predation and searching efficiency of fourth instar of predatory C. septempunctata at various densities of mustard aphid, Lipaphis erysimi (Kaltenbach) and predator was investigated under laboratory conditions. The feeding rate of predatory stage decreased at increased prey- and predator densities. Highest percent (92.80%) prey consumption was observed at initial prey density and lowest percent (40.86%) prey consumption at highest prey density by the fourth instar, though the total prey consumption increased with increase in either prey- or predator densities. Similarly, the individual prey consumption was also highest at initial predator density and lowest at highest predator density owing to the mutual interference between the predators at higher densities. The area of discovery (searching efficiency) also decreased with increase in prey- and predator densities. Handling time of predator was highest at lower prey densities, which decreased with increased prey densities. The highest percentage of prey consumption at the prey density of 50 revealed that 1:50 predator-prey ratio was the best to reduce the pest population.     

Dynamic switching in predator attack and maternal defence of prey

Predator and prey relationships are dynamic and interrelated. Thus, any offensive behaviour will vary according to differing defensive behaviours, or vice versa, within each species in any predator–prey system. However, most studies are one‐sided as they focus on just one behaviour, that of either the predator or prey. Here, we examine both predatory behaviour of an oophagus katydid and antipredator behaviour by a frog with egg‐stage parental care. Katydid offensive behaviour and predation success was greater in females and increased with predator maturity and size. Frog defensive behaviour was sex specific, probably because only mothers provide parental care. Defensive behaviour could be active, such as charging predators, or passive, such as sheltering eggs, with greater active defence against larger predators; neither was influenced by offspring age. These results are contrary to existing theory, which argues parental investment ought to be negatively correlated with parental predation risks and affected by offspring age. This study highlights the use of antipredator behaviour to test predictions of parental investment theories in amphibians. In addition, it illustrates the need to consider factors that influence both species concurrently when examining the complex interaction between predators and parents.     

Amphipod (Gammarus minus) responses to predators and predator impact on amphipod density

Recent theoretical work suggests that predator impact on local prey density will be the result of interactions between prey emigration responses to predators and predator consumption of prey. Whether prey increase or decrease their movement rates in response to predators will greatly influence the impact that predators have on prey density. In stream systems the type of predator, benthic versus water-column, is expected to influence whether prey increase or decrease their movement rates. Experiments were conducted to examine the response of amphipods (Gammarus minus) to benthic and water-column predators and to examine the interplay between amphipod response to predators and predator consumption of prey in determining prey density. Amphipods did not respond to nor were they consumed by the benthic predator. Thus, this predator had no impact on amphipod density. In contrast, amphipods did respond to two species of water-column predators (the predatory fish bluegills, Lepomis macrochirus, and striped shiners, Luxilus chrysocephalus) by decreasing their activity rates. This response led to similar positive effects on amphipod density at night by both species of predatory fish. However, striped shiners did not consume many amphipods, suggesting their impact on the whole amphipod “population” was zero. In contrast, bluegills consumed a significant number of amphipods, and thus had a negative impact on the amphipod “population”. These results lend support to theoretical work which suggests that prey behavioral responses to predators can mask the true impact that predators have on prey populations when experiments are conducted at small scales. Received: 21 March 1997 / Accepted: 15 December 1997     

Functional and numerical responses of Propylea dissecta (Col., Coccinellidae)

The functional response of a ladybeetle, Propylea dissecta, to increasing density of aphid, Aphis gossypii, was of the curvilinear shape depicting Holling's type II response with fourth instar larva being the most voracious stage when compared with adult male and female. Prey handling time by different predatory stages decreased from 65.45 to 8.72 min with increase in prey density from 25 to 800. The predator aggregation and high prey density reduces the searching efficiency of the predator. Area of discovery was highest (1.4437) when a single predator was searching at minimum aphid density (25) and lowest (0.0366) when eight predators were searching at a constant aphid density (200). Mutual interference and quest constants were 0.75 and 0.40, respectively. The reproductive numerical response, in terms of eggs laid, increased curvilinearly with prey density and female laid 70.5 ± 5.55 eggs when exposed to highest prey density (400) and 12.3 ± 0.79 eggs at lowest prey density (10). The similar shapes of both functional and reproductive responses indicate that both responses are interlinked and function simultaneously.     

Predator impacts on stream benthic prey

The impact that predators have on benthic, macroinvertebrate prey density in streams is unclear. While some studies show a strong effect of predators on prey density, others show little or no effect. Two factors appear to influence the detection of predator impact on prey density in streams. First, many field studies have small sample sizes and thus might be unable to detect treatment effects. Second, streams contain two broad classes of predators, invertebrates and vertebrates, which might have different impacts on prey density for a variety of reasons, including availability of refuge for prey and prey emigration responses to the two types of predators. In addition, predatory vertebrates have more complex prey communities than predatory invertebrates; this complexity might reduce the impact that predatory vertebrates have on prey because of indirect effects. I conducted a meta-analysis on the results of field studies that manipulate predator density in enclosures to determine (1) if predators have a significant impact on benthic prey density in streams, (2) if the impacts that predatory invertebrates and vertebrates have differ, and (3) if predatory vertebrates have different impacts on predatory prey versus herbivorous prey. The results of the meta-analysis suggest that on average predators have a significant negative effect on prey density, predatory invertebrates have a significantly stronger impact than predatory vertebrates, and predatory vertebrates do not differ in their impact on predatory versus herbivorous invertebrate prey. Three methodological variables (mesh size of enclosures, size of enclosures, and experimental duration) were examined to determine if cross correlations exist that may explain the differences in impact between predatory invertebrates and vertebrates. No correlation exists between mesh size and predator impact. Over all predators, no correlation exists between experimental duration and predator impact; however, within predatory invertebrates a correlation does exist between these variables. Also, a correlation was found between enclosure size and predator impact. This correlation potentially explains the difference in impact between predatory invertebrates and predatory vertebrates. Results of the meta-analysis suggest two important areas for future research: (1) manipulate both types of predators within the same system, and (2) examine their impacts on the same spatial scale.     

Predator-prey dynamics in an ecosystem context

Evaluating the role of fishes at the food web and ecosystem scales profits from an iterative process. At the community and population scales, prey selection by predators alters habitat selection behaviours of prey species as well as their abundance, size distributions, life histories and the consequent effects on their own prey. At the whole system scale, predation by fishes alters community structure and nutrient cycling. Thus, both direct and indirect predation effects are expressed in population structure, community composition and production processes at all trophic levels. These are the central tenets of the trophic cascade argument.
Examples are abundant and diverse. We know that predators are size selective, that resource partitioning occurs, that functional responses link the density dependence of predator and prey populations, and that predator avoidance behaviours are common. A more significant challenge exists when attempting to use this knowledge.
This presentation attempts to link theory and empiricism in forecasts of what will happen next in response to a management action or a planned experiment. Examples are drawn from whole system experiments conducted in small lakes and from large-scale manipulations of predator populations in North America's Laurentian Great Lakes. Rapid and discontinuous or non-linear responses are common. Extrapolating the lessons of mechanistic process studies proves insufficient because the context is dynamic. Inferences built from the whole ecosystem scale yield equally misleading results because the scale is too general, Resolving these problems will require a clever mix of selective applications of predator-prey theory and astute empiricism.     

Do native predators benefit from non‐native prey?

Despite knowledge on invasive species’ predatory effects, we know little of their influence as prey. Non‐native prey should have a neutral to positive effect on native predators by supplementing the prey base. However, if non‐native prey displace native prey, then an invader's net influence should depend on both its abundance and value relative to native prey. We conducted a meta‐analysis to quantify the effect of non‐native prey on native predator populations. Relative to native prey, non‐native prey similarly or negatively affect native predators, but only when studies employed a substitutive design that examined the effects of each prey species in isolation from other prey. When native predators had access to non‐native and native prey simultaneously, predator abundance increased significantly relative to pre‐invasion abundance. Although non‐native prey may have a lower per capita value than native prey, they seem to benefit native predators by serving as a supplemental prey resource.     

Prey availability in time and space is a driving force in life history evolution of predatory insects

Environmental constraints can be determinant key factors conditioning predator life history evolution. Prey seems to have conditioned life history evolution in their ladybird predator, with the predators of aphids apparently presenting faster development, greater fecundity and shorter longevity than species preying on coccids. However a rigorous comparison has never been done. We hypothesize that aphids and coccids differ by their developmental rate, abundance, and distribution in the field, which act as ecological constraints promoting life history evolution in ladybird predators. Field data reveal that aphids are ephemeral resources available in the form of large colonies randomly distributed in the habitat whereas coccids form smaller colonies that tend to be aggregated in space and available for longer periods. A comparison in laboratory conditions of two predatory species belonging to the tribe Scymnini (Coleoptera: Coccinellidae) show that the aphidophagous species lives at a faster pace than the coccidophagous: it develops faster, matures earlier, is more fecund, has a shorter reproductive life-span and allocate proportionally more fat in its gonads relative to soma. This indicates that the life histories of aphidophagous and coccidophagous ladybird predators appear to have evolved in response to particular patterns of prey availability in time and space. Under the light of these results, the existence of a slow-fast continuum in ladybirds is briefly addressed.     

Death feigning as an adaptive anti‐predator behaviour: Further evidence for its evolution from artificial selection and natural populations

Death feigning is considered to be an adaptive antipredator behaviour. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: (a) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and (b) comparison of the death‐feigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of death‐feigning behaviour was demonstrated in another prey–predator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predator‐free populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning.     

Handling time promotes the coevolution of aggregation in predator-prey systems

Predators often have type II functional responses and live in environments where their life history traits as well as those of their prey vary from patch to patch. To understand how spatial heterogeneity and predator handling times influence the coevolution of patch preferences and ecological stability, we perform an ecological and evolutionary analysis of a Nicholson-Bailey type model. We prove that coevolutionarily stable prey and searching predators prefer patches that in isolation support higher prey and searching predator densities, respectively. Using this fact, we determine how environmental variation and predator handling times influence the spatial patterns of patch preferences, population abundances and per-capita predation rates. In particular, long predator handling times are shown to result in the coevolution of predator and prey aggregation. An analytic expression characterizing ecological stability of the coevolved populations is derived. This expression implies that contrary to traditional theoretical expectations, predator handling time can stabilize predator-prey interactions through its coevolutionary influence on patch preferences. These results are shown to have important implications for classical biological control.     

Predation across spatial scales in heterogeneous environments

A hierarchy of scales is introduced to the spatially heterogeneous Lotka-Volterra predator-prey diffusion model, and its effects on the model's spatial and temporal behavior are studied. When predators move on a large scale relative to prey, local coupling of the predator-prey interaction is replaced by global coupling. Prey with low dispersal ability become narrowly confined to the most productive habitats, strongly amplifying the underlying spatial pattern of the environment. As prey diffusion rate increases, the prey distribution spreads out and predator abundance declines. The model retains neutrally stable Lotka-Volterra temporal dynamics: different scales of predator and prey dispersal do not stabilize the interaction. The model predicts that, for prey populations that are limited by widely ranging predators, species with low dispersal ability should be restricted to discrete high density patches, and those with greater mobility should be more uniformly distributed at lower density.     

Individual‐based models of cod movement and population dynamics

Understanding the strength and diversity of predator‐prey interactions among species is essential to understand ecosystem consequences of population‐level variation. Directly quantifying the predatory behaviour of wild fishes at large spatial scales (>100 m) in the open sea is fraught with difficulties. To date the only empirical approach has been to search for correlations in the abundance of predators and their putative prey. As an example we use this approach to search for predators of the keystone crown‐of‐thorns starfish. We show that this approach is unlikely to detect predator–prey linkages because the theoretical relationship is non‐linear, resulting in multiple possible prey responses for single given predator abundance. Instead we suggest some indication of the strength and ecosystem importance of a predator–prey relationship can be gained by using the abundance of both predators and their putative prey to parameterize functional response models.     

Predator personality structures prey communities and trophic cascades

Intraspecific variation is central to our understanding of evolution and population ecology, yet its consequences for community ecology are poorly understood. Animal personality – consistent individual differences in suites of behaviours – may be particularly important for trophic dynamics, where predator personality can determine activity rates and patterns of attack. We used mesocosms with aquatic food webs in which the top predator (dragonfly nymphs) varied in activity and subsequent attack rates on zooplankton, and tested the effects of predator personality. We found support for four hypotheses: (1) active predators disproportionately reduce the abundance of prey, (2) active predators select for predator‐resistant prey species, (3) active predators strengthen trophic cascades (increase phytoplankton abundance) and (4) active predators are more likely to cannibalise one another, weakening all other trends when at high densities. These results suggest that intraspecific variation in predator personality is an important determinant of prey abundance, community composition and trophic cascades.     

Pulsed-resource dynamics increase the asymmetry of antagonistic coevolution between a predatory protist and a prey bacterium

Temporal resource fluctuations could affect the strength of antagonistic coevolution through population dynamics and costs of adaptation. We studied this by coevolving the prey bacterium Serratia marcescens with the predatory protozoa Tetrahymena thermophila in constant and pulsed-resource environments for approximately 1300 prey generations. Consistent with arms race theory, the prey evolved to be more defended, whereas the predator evolved to be more efficient in consuming the bacteria. Coevolutionary adaptations were costly in terms of reduced prey growth in resource-limited conditions and less efficient predator growth on nonliving resource medium. However, no differences in mean coevolutionary changes or adaptive costs were observed between environments, even though resource pulses increased fluctuations and mean densities of coevolving predator populations. Interestingly, a surface-associated prey defence mechanism (bacterial biofilm), to which predators were probably unable to counter-adapt, evolved to be stronger in pulsed-resource environment. These results suggest that temporal resource fluctuations can increase the asymmetry of antagonistic coevolution by imposing stronger selection on one of the interacting species.     

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito, Toxorhynchites towadensis

Effects of prey density, prey instar, and patch size on the development of the predatory mosquito larva, Toxorhynchites towadensis, were investigated in the laboratory. Survivors of T. towadensis showed different developmental patterns in relation to prey age structure. All predatory larvae in containers with only second instar prey developed into the third instar. However, in several containers with fourth instar prey, mortality of predators was observed. During the third instar, no predatory larva died, but both prey density and prey instar significantly affected the survival of predators during their fourth instar. Large prey size promoted large predator adults, and predatory larvae which grew up in small surface containers responded by developing to large sizes than those in large containers. Larval developmental time of the predators differed in each treatment. During first and second instars, faster predator development was observed in containers with small surface areas and containing young prey individuals. However, when development was enhanced by the presence of old prey individuals, no surface effect was observed. The fastest predator development was observed with prey of mixed instars and high density. This study suggests that a small surface container containing prey of mixed instars and high density is suitable for development of predators.     

Are Infaunal Predators Important in Structuring Marine Soft-Bottom Communities?

The role of infaunal predators in structuring marine soft-bottomcommunities was evaluated according to these predators': 1)effects on prey density based on manipulative field experiments,2) feeding rates, 3) effects on prey distribution, 4) effectson species diversity, and 5) interactions with their prey. Estimatesof feeding rates indicate that many predatory taxa have thepotential to reduce the size of prey populations and suggestthat nemerteans are likely to have a larger impact on infaunalabundances than polychaetes. Infaunal predators have been demonstratedto have a significant effect on infaunal densities and to affectthe spatial and temporal distribution of their prey. The effectsof these predators on species diversity apparently depend onthe predator and the diversity of the system. These conclusionsmay not be applicable to all soft-bottom habitats or all groupsof infaunal predators because they are based on studies of veryfew taxa conducted almost exclusively in intertidal, unvegetated,mud habitats. Additional studies are needed on the effects ofpredation by infauna on infaunal population dynamics and onthe mechanisms of interactions between predator and prey. Furtherinvestigation will probably reveal that different groups ofinfaunal predators play different roles in structuring soft-bottomcommunities.     

Scaling up population dynamic processes in a ladybird–aphid system

Here, we study how scaling up to the metapopulation level affects predictions of a population dynamics model motivated by an aphidophagous predator–aphid system. The model incorporates optimization of egg distribution in predatory females, cannibalism among their offspring, and self-regulation of the prey population. These factors determine the within-year dynamics of the system and translate the numbers of prey and predator individuals at the beginning of the season into their numbers at the end of the season at the level of one patch—one suitable host plant or a group of these. At the end of each season, all populations of prey and all populations of predators are mixed (this simulates aphid host-alternation and ladybird migration to hibernation sites), and then redistributed at the beginning of the next season. Prey individuals are distributed at random among the patches as a “prey rain”, while adult predators that survived from the previous season optimize the distribution of their offspring, in that they prefer patches with sufficient amount of prey and absence of other predators. This redistribution followed by within-season dynamics is then iterated over many seasons. We look at whether small-scale trends in population dynamics predicted by this model are consistent with large-scale outcomes. Specifically, we show that even on the metapopulation scale, the impact of predators on prey metapopulation is relatively low. We further show how the dates of predator arrival to and departure from the system affect the qualitative behaviour of the model predictions.     

Effects of predator-specific defence on biodiversity and community complexity in two-trophic-level communities

Summary Antipredator strategies employed by prey may be specific (effective against only one type of predator) or non-specific (effective against all predators). To examine the effects of the specificity of antipredator behaviour on biodiversity and community complexity, we analyse mathematical models including both evolutionary and population dynamics of a system including multiple prey species and multiple predator species. The models assume that all predator species change in their prey choice and all prey species have evolutionary change in their antipredator effort in evolution. The traits of each species change in an adaptive manner, whose rate is proportional to the slope of their fitness function. We calculate community complexity, resource-overlap between predators, an index of biodiversity and other properties of the coevolutionarily stable community for two cases: (1) all prey species have non-specific antipredator behaviour and (2) all prey species have predator-specific defence. Predator-specificity in defence increases community complexity, resource-overlap between predators, the total abundance of predators and the ratio of predator to prey abundance. Specific defence also decreases the number of isolated subwebs within the entire foodweb.