Evolution mediates the effects of apex predation on aquatic food webs

Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.     

Effects of extinction on food web structures on an evolutionary time scale

Extinction affected food web structure in paleoecosystems. Recent theoretical studies that examined the effects of extinction intensity on food web structure on ecological time scales have considered extinction to involve episodic events, with pre-extinction food webs becoming established without dynamics. However, in terms of the paleontological time scale, food web structures are generated from feedback with repeated extinctions, because extinction frequency is affected by food web structure, and food web structure itself is a product of previous extinctions. We constructed a simulation model of changes in tri-trophic-level food webs to examine how continual extinction events affect food webs on an evolutionary time scale. We showed that under high extinction intensity (1) species diversity, especially that of consumer species, decreased; (2) the total population density at each trophic level decreased, while the densities of individual species increased; and (3) the trophic link density of the food web increased. In contrast to previous models, our results were based on an assumption of long-term food web development and are able to explain overall trends posited by empirical investigations based on fossil records.     

Paradox of marine protected areas: suppression of fishing may cause species loss

A number of fish and invertebrate stocks have been depleted by overexploitation in recent years. To address this, marine protected areas (MPAs) are often established to protect biodiversity and recover stocks. We analyzed the potential impact of establishing MPAs on marine ecosystems using mathematical models. We demonstrate that establishment of an MPA can sometimes result in a considerable decline, or even extinction, of a species. We focus on a prey–predator system in two patches, one exposed to fishing activity and the other protected (MPA). Our analyses reveal that the establishment of the MPA can cause a reduction in prey abundance, and even extinction of the prey. Such unintended consequences are more likely to occur if the predator species is a generalist and if the MPA is intended to protect only the predatory species. Further, a mobile predator that migrates adaptively rather than randomly is associated with a greater reduction in prey abundance.     

Shift in predation regime mediates diversification of foraging behaviour in a dragonfly genus

1. Behavioural adaptations to avoid and evade predators are common. Many studies have investigated population divergence in response to changes in predation regime within species, but studies exploring interspecific patterns are scant. Studies on interspecific divergence can infer common outcomes from evolutionary processes and highlight the role of environmental constraints in shaping species traits. 2. Species of the dragonfly genus Leucorrhinia underwent well‐studied shifts from habitats being dominated by predatory fish (fish lakes) to habitat being dominated by predatory invertebrates (dragonfly lakes). This change in top predators resulted in a set of adaptive trait modifications in response to the different hunting styles of both predator types: whereas predatory fish actively search and pursue prey, invertebrate predator follow a sit‐and‐wait strategy, not pursuing prey. 3. Here it is shown that the habitat shift‐related change in selection regime on larval Leucorrhinia caused species in dragonfly lakes to evolve increased larval foraging and activity, and results suggest that they lost the ability to recognise predatory fish. 4. The results of the present study highlight the impact of predators on behavioural trait diversification with habitat‐specific predation regimes selecting for distinct behavioural expression.     

Fish–prey interactions in,and associated data from,a temperate stream of the Yura River,Kyoto, Japan

Although quantitative data on interspecific interactions within complex food webs are essential for evaluation of assumptions, hypotheses, and predictions of ecological theories; empirical studies yielding quantitative data on complex food webs are very limited. Ecological information on body size, habitat use, and seasonality of the component species of food webs aids in determining the mechanisms of food web structures. Ideally, ecological information on component species should be obtained contemporaneously when used to describe quantitative food webs, but such observations and sampling strategies are labor intensive and thus have been rarely described. We conducted year-round samplings of, and performed observations on, a temperate stream: the upper reaches of the Yura River, Kyoto, Japan. We derived quantitative data on the abundance, biomass, body mass, microhabitat use, and those seasonality of 7 fish species and 167 invertebrate taxa of the temperate stream food web. In addition, we estimated the per mass consumption rates of 7 predatory fish species, consuming 183 prey invertebrates, and the ratios between the per mass consumption rates of the 7 predatory fish species and the production rates of 78 prey invertebrates in each trophic link. All fishes and aquatic invertebrates were identified to species or lowest possible taxon. Our data may contribute to the construction of mathematical models explaining the behavior of stream communities/ecosystems.     

Food resource and temporal partitioning amongst a guild of predatory agroecosystem-inhabiting ant species

Prey diversity and temporal foraging patterns of six abundant,predatory ant species were investigated seasonally in an agroecosystem with two main vegetable crops.Pheidole sp.demonstrated the highest predation success and therefore appears to be the dominant species while Tapinoma melanocephalum showed the lowest success under the natural field conditions.Investigation of prey diversity and temporal activity patterns with the null model tests of niche overlap revealed a significant overlap indicating that t...     

Who eats whom in a pool? A comparative study of prey selectivity by predatory aquatic insects

Predatory aquatic insects are a diverse group comprising top predators in small fishless water bodies. Knowledge of their diet composition is fragmentary, which hinders the understanding of mechanisms maintaining their high local diversity and of their impacts on local food web structure and dynamics. We conducted multiple-choice predation experiments using nine common species of predatory aquatic insects, including adult and larval Coleoptera, adult Heteroptera and larval Odonata, and complemented them with literature survey of similar experiments. All predators in our experiments fed selectively on the seven prey species offered, and vulnerability to predation varied strongly between the prey. The predators most often preferred dipteran larvae; previous studies further reported preferences for cladocerans. Diet overlaps between all predator pairs and predator overlaps between all prey pairs were non-zero. Modularity analysis separated all primarily nectonic predator and prey species from two groups of large and small benthic predators and their prey. These results, together with limited evidence from the literature, suggest a highly interconnected food web with several modules, in which similarly sized predators from the same microhabitat are likely to compete strongly for resources in the field (observed Pianka's diet overlap indices >0.85). Our experiments further imply that ontogenetic diet shifts are common in predatory aquatic insects, although we observed higher diet overlaps than previously reported. Hence, individuals may or may not shift between food web modules during ontogeny.     

Biological hierarchies and the nature of extinction

Hierarchy theory recognises that ecological and evolutionary units occur in a nested and interconnected hierarchical system, with cascading effects occurring between hierarchical levels. Different biological disciplines have routinely come into conflict over the primacy of different forcing mechanisms behind evolutionary and ecological change. These disconnects arise partly from differences in perspective (with some researchers favouring ecological forcing mechanisms while others favour developmental/historical mechanisms), as well as differences in the temporal framework in which workers operate. In particular, long‐term palaeontological data often show that large‐scale (macro) patterns of evolution are predominantly dictated by shifts in the abiotic environment, while short‐term (micro) modern biological studies stress the importance of biotic interactions. We propose that thinking about ecological and evolutionary interactions in a hierarchical framework is a fruitful way to resolve these conflicts. Hierarchy theory suggests that changes occurring at lower hierarchical levels can have unexpected, complex effects at higher scales due to emergent interactions between simple systems. In this way, patterns occurring on short‐ and long‐term time scales are equally valid, as changes that are driven from lower levels will manifest in different forms at higher levels. We propose that the dual hierarchy framework fits well with our current understanding of evolutionary and ecological theory. Furthermore, we describe how this framework can be used to understand major extinction events better. Multi‐generational attritional loss of reproductive fitness (MALF) has recently been proposed as the primary mechanism behind extinction events, whereby extinction is explainable solely through processes that result in extirpation of populations through a shutdown of reproduction. While not necessarily explicit, the push to explain extinction through solely population‐level dynamics could be used to suggest that environmentally mediated patterns of extinction or slowed speciation across geological time are largely artefacts of poor preservation or a coarse temporal scale. We demonstrate how MALF fits into a hierarchical framework, showing that MALF can be a primary forcing mechanism at lower scales that still results in differential survivorship patterns at the species and clade level which vary depending upon the initial environmental forcing mechanism. Thus, even if MALF is the primary mechanism of extinction across all mass extinction events, the primary environmental cause of these events will still affect the system and result in differential responses. Therefore, patterns at both temporal scales are relevant.     

Network position of hosts in food webs and their parasite diversity

Parasites are ubiquitous in ecological communities but it is only recently that they have been routinely included in food web studies. Using recently published data and the tool of network analysis, we elucidate features associated with the pattern of parasitism in ecological communities. First we show here that parasitism is non‐random in food webs. Second we demonstrate that parasite diversity, the number of parasite species harboured by a host species, is related to the network position of a host species. Specifically, a host species with high parasite diversity tends to have a wide diet range, occupy a network position close to many prey species, or occupy a network position that can better accumulate resources from species at lower trophic levels. Lastly our results also suggest that a host species with higher vulnerability to predators, being at a network position close to many predatory species, or being involved in many different food chains, tends to be important in parasite transmission.     

Infochemical-mediated intraguild interactions among three predatory mites on cassava plants

Carnivorous arthropods exhibit complex intraspecific and interspecific behaviour among themselves when they share the same niche or habitat and food resources. They should simultaneously search for adequate food for themselves and their offspring and in the meantime avoid becoming food for other organisms. This behaviour is of great ecological interest in conditions of low prey availability. We examined by means of an olfactometer, how volatile chemicals from prey patches with conspecific or heterospecific predators might contribute to shaping the structure of predator guilds. To test this, we used the exotic predatory mites Typhlodromalus manihoti and T. aripo, and the native predatory mite Euseius fustis, with Mononychellus tanajoa as the common prey species for the three predatory mite species. We used as odour sources M. tanajoa-infested cassava leaves or apices with or without predators. T. manihoti avoided patches inhabited by the heterospecifics T. aripo and E. fustis or by conspecifics when tested against a patch without predators. Similarly, both T. aripo and E. fustis females avoided patches with con- or heterospecifics when tested against a patch without predators. When one patch contained T. aripo and the other T. manihoti, females of the latter preferred the patch with T. aripo. Thus, T. manihoti is able to discriminate between odours from patches with con- and heterospecifics. Our results show that the three predatory mite species are able to assess prey patch profitability using volatiles. Under natural conditions, particularly when their food sources are scarce, the three predatory mite species might be involved in interspecific and/or intraspecific interactions that can substantially affect population dynamics of the predators and their prey.     

Effects of evolutionary changes in prey use on the relationship between food web complexity and stability

The relationship between food web complexity and stability has been the subject of a long-standing debate in ecology. Although rapid changes in the food web structure through adaptive foraging behavior can confer stability to complex food webs, as reported by Kondoh (Science 299:1388–1391, 2003), the exact mechanisms behind this adaptation have not been specified in previous studies; thus, the applicability of such predictions to real ecosystems remains unclear. One mechanism of adaptive foraging is evolutionary change in genetically determined prey use. We constructed individual-based models of evolution of prey use by predators assuming explicit population genetics processes, and examined how this evolution affects the stability (i.e., the proportion of species that persist) of the food web and whether the complexity of the food web increased the stability of the prey–predator system. The analysis showed that the stability of food webs decreased with increasing complexity regardless of evolution of prey use by predators. The effects of evolution on stability differed depending on the assumptions made regarding genetic control of prey use. The probabilities of species extinctions were associated with the establishment or loss of trophic interactions via evolution of the predator, indicating a clear link between structural changes in the food web and community stability.     

Biotic and abiotic factors driving the diversification dynamics of Crocodylia

Species diversity patterns are governed by complex interactions among biotic and abiotic factors over time and space, but are essentially the result of the diversification dynamics (differential speciation and extinction rates) over the long-term evolutionary history of a clade. Previous studies have suggested that temporal variation in global temperature drove long-term diversity changes in Crocodylia, a monophyletic group of large ectothermic organisms. We use a large database of crocodylian fossil occurrences (192 spp.) and body mass estimations, under a taxic approach, to characterize the global diversification dynamics of crocodylians since the Cretaceous, and their correlation with multiple biotic and abiotic factors in a Bayesian framework. The diversification dynamic of crocodylians, which appears to have originated in the Turonian (c. 92.5 Ma), is characterized by several phases with high extinction and speciation rates within a predominantly low long-term mean rate. Our results reveal long-term diversification dynamics of Crocodylia to be a highly complex process driven by a combination of biotic and abiotic factors which influenced the speciation and extinction rates in dissimilar ways. Higher crocodylian extinction rates are related to low body mass disparity, indicating selective extinctions of taxa at both ends of the body mass spectrum. Speciation rate slowdowns are noted when the diversity of the clade is high and the warm temperate climatic belt is reduced. Our finding supports the idea that temporal variations of body mass disparity, self-diversity, and the warm climate belt size provided more direct mechanistic explanations for crocodylian diversification than do proxies of global temperature.     

Seasonally fluctuating resources and temporal variability of interspecific competition

Summary The influence of seasonal availability of two critical resources (food and substrates from which food was harvested) on interspecific competition between striped surfperch (Embiotoca lateralis) and black surfperch (Embiotoca jacksoni) was examined. There was a strong depth-related gradient in density of prey and in cover of foliose algae; both declined with increasing bottom depth. Density of prey was reduced 5–10 fold during the winter season, but cover of substrates remained constant throughout the year. Although both fishes co-occurred throughout the same depth range, striped surfperch were more common in shallow habitats and black surfperch were more abundant deeper. Local abundance and distribution patterns of both surfperch species did not change seasonally. Stepwise regression analyses suggested that availability of favored substrates was a proximate influence on local patterns of surfperch distribution and abundance, and that interspecific competition depressed abundance of the two species to the same degree. Removal experiments conducted during the cold-water season revealed that interspecific competition influenced depth distribution of black surfperch but not striped surfperch. Seasonal change in density of prey was accompanied by marked changes in overlap in use of foraging substrates by the surfperches. The pattern of change in interspecific overlap suggested that surfperch competed for food only when prey were seasonally scarce. There was no difference in the agonistic tendencies of the two fishes, and the absolute and relative frequency of interspecific chases was independent of food level. These results have important implications regarding the impact of temporal variability of interspecific competition in natural communities. In the surfperch system, competition was characterized by constant and time-varying elements that had symmetrical and asymmetrical effects and involved both interference and exploitation mechanisms.     

Rainfall and hydrological stability alter the impact of top predators on food web structure and function

Climate change will alter the distribution of rainfall, with potential consequences for the hydrological dynamics of aquatic habitats. Hydrological stability can be an important determinant of diversity in temporary aquatic habitats, affecting species persistence and the importance of predation on community dynamics. As such, prey are not only affected by drought‐induced mortality but also the risk of predation [a non‐consumptive effect (NCE)] and actual consumption by predators [a consumptive effect (CE)]. Climate‐induced changes in rainfall may directly, or via altered hydrological stability, affect predator–prey interactions and their cascading effects on the food web, but this has rarely been explored, especially in natural food webs. To address this question, we performed a field experiment using tank bromeliads and their aquatic food web, composed of predatory damselfly larvae, macroinvertebrate prey and bacteria. We manipulated the presence and consumption ability of damselfly larvae under three rainfall scenarios (ambient, few large rainfall events and several small rainfall events), recorded the hydrological dynamics within bromeliads and examined the effects on macroinvertebrate colonization, nutrient cycling and bacterial biomass and turnover. Despite our large perturbations of rainfall, rainfall scenario had no effect on the hydrological dynamics of bromeliads. As a result, macroinvertebrate colonization and nutrient cycling depended on the hydrological stability of bromeliads, with no direct effect of rainfall or predation. In contrast, rainfall scenario determined the direction of the indirect effects of predators on bacteria, driven by both predator CEs and NCEs. These results suggest that rainfall and the hydrological stability of bromeliads had indirect effects on the food web through changes in the CEs and NCEs of predators. We suggest that future studies should consider the importance of the variability in hydrological dynamics among habitats as well as the biological mechanisms underlying the ecological responses to climate change.     

Trophic interactions affect the population dynamics and risk of extinction of basal species in food webs

This paper addresses effects of trophic complexity on basal species, in a Lotka–Volterra model with stochasticity. We use simple food web modules, with three trophic levels, and expose every species to random environmental stochasticity and analyze (1) the effect of the position of strong trophic interactions on temporal fluctuations in basal species’ abundances and (2) the relationship between fluctuation patterns and extinction risk. First, the numerical simulations showed that basal species do not simply track the environment, i.e. species dynamics do not simply mirror the characteristics of the applied environmental stochasticity. Second, the extinction risk of species was related to the fluctuation patterns of the species.More specifically, we show (i) that despite being forced by random stochasticity without temporal autocorrelation (i.e. white noise), there is significant temporal autocorrelation in the time series of all basal species’ abundances (i.e. the spectra of basal species are red-shifted), (ii) the degree of temporal autocorrelation in basal species time series is affected by food web structure and (iii) the degree of temporal autocorrelation tend to be correlated to the extinction risks of basal species.Our results emphasize the role of food web structure and species interactions in modifying the response of species to environmental variability. To shed some light on the mechanisms we compare the observed pattern in abundances of basal species with analytically predicted patterns and show that the change in the predicted pattern due to the addition of strong trophic interactions is correlated to the extinction risk of the basal species. We conclude that much remain to be understood about the mechanisms behind the interaction among environmental variability, species interactions, population dynamics and vulnerability before we quantitatively can predict, for example, effects of climate change on species and ecological communities. Here, however, we point out a new possible approach for identifying species that are vulnerable to environmental stochasticity by checking the degree of temporal autocorrelation in the time series of species. Increased autocorrelation in population fluctuations can be an indication of increased extinction risk.     

Temporal Patterns of Diversification across Global Cichlid Biodiversity (Acanthomorpha: Cichlidae)

The contrasting distribution of species diversity across the major lineages of cichlids makes them an ideal group for investigating macroevolutionary processes. In this study, we investigate whether different rates of diversification may explain the disparity in species richness across cichlid lineages globally. We present the most taxonomically robust time-calibrated hypothesis of cichlid evolutionary relationships to date. We then utilize this temporal framework to investigate whether both species-rich and depauperate lineages are associated with rapid shifts in diversification rates and if exceptional species richness can be explained by clade age alone. A single significant rapid rate shift increase is detected within the evolutionary history of the African subfamily Pseudocrenilabrinae, which includes the haplochromins of the East African Great Lakes. Several lineages from the subfamilies Pseudocrenilabrinae (Australotilapiini, Oreochromini) and Cichlinae (Heroini) exhibit exceptional species richness given their clade age, a net rate of diversification, and relative rates of extinction, indicating that clade age alone is not a sufficient explanation for their increased diversity. Our results indicate that the Neotropical Cichlinae includes lineages that have not experienced a significant rapid burst in diversification when compared to certain African lineages (rift lake). Neotropical cichlids have remained comparatively understudied with regard to macroevolutionary patterns relative to African lineages, and our results indicate that of Neotropical lineages, the tribe Heroini may have an elevated rate of diversification in contrast to other Neotropical cichlids. These findings provide insight into our understanding of the diversification patterns across taxonomically disparate lineages in this diverse clade of freshwater fishes and one of the most species-rich families of vertebrates.     

Availability of prey resources drives evolution of predator-prey interaction

Productivity is predicted to drive the ecological and evolutionary dynamics of predator-prey interaction through changes in resource allocation between different traits. Here we report results of an evolutionary experiment where prey bacteria Serratia marcescens was exposed to predatory protozoa Tetrahymena thermophila in low- and high-resource environments for approximately 2400 prey generations. Predation generally increased prey allocation to defence and caused prey selection lines to become more diverse. On average, prey became most defensive in the high-resource environment and suffered from reduced resource use ability more in the low-resource environment. As a result, the evolution of stronger prey defence in the high-resource environment led to a strong decrease in predator-to-prey ratio. Predation increased temporal variability of populations and traits of prey. However, this destabilizing effect was less pronounced in the high-resource environment. Our results demonstrate that prey resource availability can shape the trade-off allocation of prey traits, which in turn affects multiple properties of the evolving predator-prey system.     

Habitat subdivision causes changes in food web structure

Theory suggests that the response of communities to habitat subdivision depends on both species' characteristics and the extent to which species interact. For species with dynamics that are independent of other species, subdivision is expected to promote regional extinction as populations become small and isolated. By contrast, intermediate levels of subdivision can facilitate persistence of strongly interacting species. Consistent with this prediction, experimental subdivision lengthened persistence of some species, altering the extent of food web collapse through extinction. Extended persistence was associated with immigration rescuing a basal prey species from local extinction. As predicted by food web theory, habitat subdivision reduced population density of a top predator. Removal of this top predator from undivided microcosms increased the abundance of two other predator species, and these changes paralleled those produced by habitat subdivision. These results show that species interactions structured this community, and illustrate the need for investigations of other communities.     

Global patterns of diversification and species richness in amphibians

Geographic patterns of species richness ultimately arise through the processes of speciation, extinction, and dispersal, but relatively few studies consider evolutionary and biogeographic processes in explaining these diversity patterns. One explanation for high tropical species richness is that many species-rich clades originated in tropical regions and spread to temperate regions infrequently and more recently, leaving little time for species richness to accumulate there (assuming similar rates of diversification in temperate and tropical regions). However, the major clades of anurans (frogs) and salamanders may offer a compelling counterexample. Most salamander families are predominately temperate in distribution, but the one primarily tropical clade (Bolitoglossinae) contains nearly half of all salamander species. Similarly, most basal clades of anurans are predominately temperate, but one largely tropical clade (Neobatrachia) contains approximately 96% of anurans. In this article, I examine patterns of diversification in frogs and salamanders and their relationship to large-scale patterns of species richness in amphibians. I find that diversification rates in both frogs and salamanders increase significantly with decreasing latitude. These results may shed light on both the evolutionary causes of the latitudinal diversity gradient and the dramatic but poorly explained disparities in the diversity of living amphibian clades.     

Resource tracking in marine parasites: going with the flow?

Understanding how diversity interacts with energy supply is of broad ecological interest. Most studies to date have investigated patterns within trophic levels, reflecting a lack of food webs which include information on energy flow. We added parasites to a published marine energy‐flow food web, to explore whether parasite diversity is correlated with energy flow to host taxa. Parasite diversity was high with 36 parasite taxa affecting 40 of the 51 animal taxa. Adding parasites increased the number of trophic links per species, trophic link strength, connectance, and food chain lengths. There was evidence of an asymptotic relationship between energy flowing through a food chain and parasite diversity, although there were clear outliers. High parasite diversity was associated with host taxa which were highly connected within the food web. This suggests that energy flow through a taxon may favour parasite diversity, up to a maximal value. The evolutionary and energetic basis for that limitation is of key interest in understanding the basis for parasite diversity in natural food webs and thus their role in food web dynamics.