Michael S Singer

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Verified

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• PhD
• Professor at Wesleyan University

Growing evidence suggests that organisms with narrow niche requirements are particularly disadvantaged in small habitat patches, typical of fragmented landscapes. However, the mechanisms behind this relationship remain unclear. Dietary specialists may be particularly constrained by the availability of their food resources as habitat area shrinks. F...

How consumer diversity determines consumption efficiency is a central issue in ecology. In the context of predation and biological control, this relationship concerns predator diversity and predation efficiency. Reduced predation efficiency can result from different predator taxa eating each other in addition to their common prey (interference due...

Seemingly small ecological changes can have large, ramifying effects that defy expectations. Such are keystone effects in ecosystems. Phloem-feeding insect herbivores can act as keystone species by altering community structure and species interactions via plant-mediated or ant-mediated mechanisms. Plant responses triggered by phloem-feeders can dis...

We review evidence for predators as agents of selection for the evolution of dietary specialization by insect herbivores. Since being proposed in the 1980s, this “enemy-free space” hypothesis has garnered much attention, but relatively little testing. Most tests have used caterpillars to address the community-level prediction that generalist predat...

Remote sensing imagery can provide critical information on the magnitude and extent of damage caused by forest pests and pathogens. However, monitoring short‐term changes in deciduous forest condition caused by defoliating insects is challenging and requires approaches that directly account for seasonal vegetation dynamics. We implemented a previou...

Ecological interactions increasingly occur in the context of anthropogenic landscape alteration, such as landscape fragmentation, which engenders numerous changes to abiotic and biotic processes. Theory and empirical evidence suggest that species that are ecologically specialized or positioned at higher trophic levels are most sensitive to the effe...

Abstract The enemy‐free space hypothesis (EFSH) contends that generalist predators select for dietary specialization in insect herbivores. At a community level, the EFSH predicts that dietary specialization reduces predation risk, and this pattern has been found in several studies addressing the impact of individual predator taxa or guilds. However...

Interactions between ants and phloem‐feeding herbivores are characterised as a keystone mutualism because they restructure arthropod communities and generate trophic cascades. Keystone interactions in terrestrial food webs are hypothesised to depend on herbivore community structure and bottom‐up effects on plant growth. Here, we tested this predict...

Ant-hemipteran mutualisms are widespread interactions in terrestrial food webs with far-reaching consequences for arthropod communities. Several hypotheses address the behavioral mechanisms driving the impacts of this mutualism, but relatively few studies have considered multiple ant species simultaneously as well as interspecific and intraspecific...

A multi-trophic perspective improves understanding of the ecological and evolutionary consequences of rapid environmental change on insect herbivores. Loss of specialized enemies due to human impacts is predicted to dramatically reduce the number of tritrophic niches of herbivores compared to a bitrophic niche perspective. Habitat fragmentation and...

Reduced ecological specialization is an emerging, general pattern of ecological networks in fragmented landscapes. In plant–herbivore interactions, reductions in dietary specialization of herbivore communities are consistently associated with fragmented landscapes, but the causes remain poorly understood. We propose several hypothetical bottom–up a...

Determining the impacts of mutualistic interactions and predator diversity on food webs are two important goals in community ecology. In this study, we examined how predator community variation mediates the strength of top–down effects in the presence and absence of mutualistic interactions. We examined the impacts of predatory ant species that sim...

Research on parasite-altered feeding behavior in insects is contributing to an emerging literature that considers possible adaptive consequences of altered feeding behavior for the host or the parasite. Several recent ecoimmunological studies show that insects can adaptively alter their foraging behavior in response to parasitism. Another body of r...

The effects of predator assemblages on herbivores are predicted to depend critically on predator–predator interactions and the extent to which predators partition prey resources. The role of prey heterogeneity in generating such multiple predator effects has received limited attention. Vertebrate and arthropod insectivores constitute two co‐dominan...

Direct and indirect effects of predators are highly variable in complex communities, and understanding the sources of this variation is a research priority in community ecology. Recent evidence indicates that herbivore community structure is a primary determinant of predation strength and its cascading impacts on plants. In this study, we use varia...

Plant-insect interactions research emphasizes adaptive plasticity of plants and carnivores, such as parasitoids, implying a relatively passive role of herbivores. Current work is addressing this deficit, with exciting studies of behavioral plasticity of larval Lepidoptera (caterpillars). Here I use select examples to illustrate the diversity of beh...

Significance Dietary specialization determines an organism’s resource base as well as impacts on host or prey species. There are important basic and applied reasons to ask why some animals have narrow diets and others are more generalized, and if different regions of the Earth support more specialized interactions. We investigated site-specific hos...

Natural enemies often cause significant levels of mortality for their prey and thus can be important agents of natural selection. It follows, then, that selection should favor traits that enable organisms to escape from their natural enemies into "enemy-free space" (EFS). Natural selection for EFS was originally proposed as a general force in struc...

The myriad chemicals produced by plants may act in combination to enhance chemical defence against herbivores. Many animals have evolved the ability to harness plant secondary metabolites ( PSM s) and other chemical resources for their own defence, but few studies have addressed the compelling notion that non‐human animals combine exogenous chemica...

Food-for-protection mutualisms between ants and sap-feeding herbivores can alter the structure of insect food webs. By providing a food reward to ants, sap-feeding insects can modify ant interactions with other species through changes in ant behavior, density, or community structure. This research tests mechanisms underlying the trophic consequence...

Host manipulation theory predicts that a change in host behavior increases parasite fitness. Variation in host diet mediates host-parasite interactions and the way in which parasites control host dietary factors can play a critical role in parasite success. Grammia incorrupta is a grazing generalist caterpillar that is frequently parasitized by the...

The effectiveness of anti-predator traits, such as warning signals and camouflage, has rarely been quantified from a phylogenetic community ecology perspective. Here we use a phylogenetic comparative analysis to test the association between several putative anti-predator traits and bird predation risk in an assemblage of caterpillar species. We syn...

Background/Question/Methods The effects of multiple predator taxa on densities of a shared prey taxon can be additive or non-additive, the latter being either synergistically positive or antagonistic. Most studies show evidence for additive or antagonistic effects, but the underlying mechanisms have received limited study. One prominent hypothesis...

Some insect herbivores sequester plant secondary metabolites (PSMs) for their own defense, raising the interesting possibility that grazing herbivores are defended by combinations of PSMs from different plant species. In this study, we tested the hypothesis that the grazing caterpillar, Grammia incorrupta, deters the ant, Aphaenogaster cockerelli,...

A rapidly advancing area of ecological immunology concerns the effects of diet on animals' immunological responses to parasites and pathogens. Here, we focus on diet-mediated ecological immunology in herbivorous insects, in part because these organisms commonly experience nutritional limitations from their diets of plants. Nutritional immunology hi...

Significance This study shows the far-reaching effects of herbivore dietary specialization on the ecological and evolutionary dynamics of carnivore–herbivore–plant interactions. First, we test the long-standing hypothesis that dietary specialization of insect herbivores mediates the strength of bird predation on herbivores. Accounting for phylogene...

Advances in ecological immunity have illustrated that, like vertebrates, insects exhibit adaptive immunity, including induced changes in feeding behavior that aid the immune system. In particular, recent studies have pointed to the importance of protein intake in mounting an immune response. In this study, we tested the hypothesis that the polyphag...

Adaptive transgenerational plasticity is predicted to evolve when parental environments are predictive of offspring environments, and when reliable cues are available to induce adaptive offspring phenotypes. In plant-feeding insects, parental diet may have pronounced effects on offspring performance, as specific host plants may provide induction cu...

Variation in host diet mediates host-parasite interactions and it is important to assess which dietary factors play a critical role in host defense and parasite success. Grammia incorrupta is a grazing caterpillar that ingests and sequesters plant secondary metabolites (PSMs) called pyrrolizidine alkaloids (PAs) from a subset of host-plant species...

Background/Question/Methods The enemy-free space hypothesis (EFSH) predicts that dietary specialist herbivores are superior to generalists in using host plants for defense or refuge from enemies. The EFSH has received strong support from herbivore community-level tests with generalist predators, especially predaceous ants. Studies using predaceou...

Herbivore-carnivore interactions are influenced by the plants on which herbivores feed. Accordingly, dietary generalist herbivores have been shown to experience differential risk of mortality from carnivores on different host-plant species. Here, we investigate whether caterpillar density and host-plant quality play a role in driving variation in g...

Introduction While it had long been recognized that herbivores are simultaneously influenced by natural enemies (Hairston et al. 1960) and plant defences (Fraenkel 1959), Price et al. (1980) were among the first to argue forcefully that these dual factors must be considered together. They argued that ‘[w]e cannot understand the plant–herbivore inte...

Background/Question/Methods The enemy-free space hypothesis (EFSH) predicts that dietary specialist herbivores are superior to generalists in using host plants for defense or refuge from enemies. The EFSH has received support from tests with generalist invertebrate predators of insect herbivores. Here, we test the EFSH with respect to bird predat...

Ecological specialization is a fundamental and well-studied concept, yet its great reach and complexity limit current understanding in important ways. More than 20 years after the publication of D. J. Futuyma and G. Moreno's oft-cited, major review of the topic, we synthesize new developments in the evolution of ecological specialization. Using ins...

Several influential hypotheses in plant-herbivore and herbivore-predator interactions consider the interactive effects of plant quality, herbivore diet breadth, and predation on herbivore performance. Yet individually and collectively, these hypotheses fail to address the simultaneous influence of all three factors. Here we review existing hypothes...

Effects of plant traits on herbivore-carnivore interactions are well documented in component communities but are not well understood at the level of large, complex communities. We report on a 2-year field experiment testing mechanisms by which variation in food quality among eight temperate forest tree species alters avian suppression of an assembl...

Factors including host abundance, quality, and the degree to which hosts provide enemy-free space (EFS) may drive host plant choice by phytophagous insects. Herbivores may also experience fitness tradeoffs among hosts, promoting polyphagy. The fall webworm Hyphantria cunea is a dietary generalist that feeds on a broad array of trees across its geog...

Background/Question/Methods The mechanisms by which plants modify herbivore suppression by carnivores are important yet infrequently studied at a community-wide level. Interaction modifications can arise from two distinct mechanisms (trait-related and density-related) with different consequences for the evolutionary ecology of species interaction...

The current focus on tri-trophic interactions has emphasized adaptive plasticity of plant defense and behavioral responses of carnivores such as parasitoids, with relatively little consideration for counter-adaptations by herbivores. This study investigates herbivore self-medication behavior: changes in ingestion of plant toxins as resistance again...

This study investigates complex effects of parasitoid infection on herbivore diet choice. Specifically, we examine how immunological resistance, parasitoid infection stage, and parasitoid taxonomic identity affect the pharmacophagous behavior of the polyphagous caterpillar, Grammia incorrupta (Arctiidae). Using a combination of lab and field experi...

Background/Question/Methods Determinants of dietary specialization in insect herbivores may involve plant-herbivore (bi-trophic) or plant-herbivore-carnivore (tri-trophic) interactions. Although they represent a minority of insect herbivore species, dietary generalists offer a relatively unexplored opportunity to address the role of bi-trophic and...

Background/Question/Methods Generalist insect herbivores show host-plant dependent differences in both bi-trophic performance (i.e., growth) and parasitism frequencies. The relationship between bi-trophic performance and realized parasitism (i.e., parasitoid emergence) on a given host plant may vary according to factors including parasitoid attac...

Tritrophic interactions may include directly harmful effects of host plants on herbivores, and directly or indirectly harmful effects of host plants on the natural enemies of herbivores. Tritrophic interactions involving parasitoids and predators have received considerable attention but less is known about how host plants affect entomopathogens. We...

Background/Question/Methods Host plant choice by phytophagous insects may be driven by factors including host abundance, host quality, and the degree to which host plants provide enemy free space. These factors may also present herbivores with fitness trade-offs among hosts, promoting dietary generalism and preferences that maximize different fitne...

Background/Question/Methods The preponderance of host specificity among insect herbivores may be due to ecological advantages of dietary specialists over generalists. For example, specialists might be superior in using host plants for defense or refuge from enemies (enemy-free space). Previous work suggests that specialist herbivores can enjoy an e...

Self-medication is a specific therapeutic behavioral change in response to disease or parasitism. The empirical literature on self-medication has so far focused entirely on identifying cases of self-medication in which particular behaviors are linked to therapeutic outcomes. In this study, we frame self-medication in the broader realm of adaptive p...

Adaptive diversification is a process intrinsically tied to species interactions. Yet, the influence of most types of interspecific interactions on adaptive evolutionary diversification remains poorly understood. In particular, the role of mutualistic interactions in shaping adaptive radiations has been largely unexplored, despite the ubiquity of m...

The evolutionary ecology of polyphagy by phytophagous insects has been overshadowed by an intense focus on the evolutionary ecology of their host specificity. This bias reflects the preponderance of host specificity in phytophagous insects, and its fascinating consequences for community structure and evolutionary diversification. Truly, the study o...

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecol...

A conceptual divide exists between ecological and evolutionary approaches to understanding adaptive radiation, although the phenomenon is inherently both ecological and evolutionary. This divide is evident in studies of phytophagous insects, a highly diverse group that has been frequently investigated with the implicit or explicit goal of understan...

Insect outbreaks are expected to increase in frequency and intensity with projected changes in global climate through direct effects of climate change on insect populations and through disruption of community interactions. Although there is much concern about mean changes in global climate, the impact of climatic variability itself on species inter...

The polyphagous arctiid Grammia geneura appears well adapted to utilize for its protection plant pyrrolizidine alkaloids of almost all known structural types. Plant-acquired alkaloids that are maintained through all life-stages include various classes of macrocyclic diesters (typically occurring in the Asteraceae tribe Senecioneae and Fabaceae), ma...

Taste sensation and food selection by animals can change adaptively in response to experience, for example to redress specific nutrient deficiencies. We show here, in two species of caterpillar, that infection by lethal parasites alters the taste of specific phytochemicals for the larvae. Given that these compounds are toxic to the parasites and ar...

Evidence is presented that the polyphagous arctiid Estigmene acrea is well adapted to sequester and specifically handle pyrrolizidine alkaloids of almost all known structural types representative of the major plant families with pyrrolizidine alkaloid-containing species, i.e. Asteraceae with the tribes Senecioneae and Eupatorieae, Boraginaceae, Fab...

The relative importance,of food,quality vs. enemy-free,space remains,an unresolved,but central issue in the evolutionary,ecology,of host use by phytophagous,insects. In this study, we investigate their relative importance in determining host-plant use by a generalist caterpillar, Estigmene acrea , We therefore conclude,that the balance,between,bene...

The relative importance of food quality and enemy-reduced space is a central but unresolved issue in the evolutionary ecology of host use by phytophagous insects. Indeed, a practical obstacle to experimentally disentangling the functional roles of these factors is the host specificity of insect herbivores, particularly toxic plant specialists. In t...

The relative importance of food quality and enemy‐reduced space is a central but unresolved issue in the evolutionary ecology of host use by phytophagous insects. Indeed, a practical obstacle to experimentally disentangling the functional roles of these factors is the host specificity of insect herbivores, particularly toxic plant specialists. In t...

1. Seventy-seven individual last-instar caterpillars foraging in the field were examined for 6 h each. They represented four species of Arctiidae of similar size and habitat use. Two, Hypocrisias minima and Pygarctia roseicapitis, are specialists restricted to particular plant genera. The other two, Grammia geneura and Estigmene acrea, are extreme...

The profiles of pyrrolizidine alkaloids (PAs) in the two highly polyphagous arctiids Estigmene acrea and Grammia geneura and their potential PA sources in southeastern Arizona were compiled. One of four species of Boraginaceae, Plagiobothrys arizonicus, contained PAs; this is the first PA record for this plant species. The principle PA sources are...

Caterpillars of the polyphagous arctiid, Grammia geneura, have a single cell in the medial galeal sensillum that responds to some sugars and to some amino acids. After conditioning on artificial diet containing unbalanced amounts of carbohydrate and protein, the responses of this cell alter. After protein-biased food it increases slightly, but afte...

Six-hour continuous observations on the arctiid caterpillar, Pygarctia roseicapitis, were made under natural conditions in the field, and all foraging-related activities were recorded. Individuals invariably cut veins of the latex-rich host plants before feeding distal to the cuts. Seven percent of the time was spent in this vein-cutting behavior,...

Electrophysiological recordings from taste sensilla of the caterpillar Estigmene acrea with the pyrrolizidine alkaloid (PA) seneciphylline N-oxide demonstrated that extensive feeding on plants rich in PAs caused a loss in response of the PA-sensitive cell in the lateral styloconic sensillum on the galea. The effect could be repeated using pure PAs...

Electrophysiological recordings from taste sensilla of the caterpillar Estigmene acrea with the pyrrolizidine alkaloid, seneciphylline N-oxide, demonstrated that prior feeding on plants with pyrrolizidine alkaloids caused an increase in responsiveness of the PA-sensitive cells in two sensilla, relative to feeding on plants without such chemicals. R...

While the importance of omnivory in community and food web ecology has received recent recognition, the behavioral basis of omnivory has not been thoroughly explored. Here we argue that understanding the basis of food mixing (i.e., eating different food types) and food selection behavior is central to understanding the causes and con-sequences of o...

Despite the vast diversity of parasitic insects and their importance in natural and agricultural communities, our knowledge of what determines their patterns of association with hosts remains sparse. Unlike most parasites that tend to be specialized, parasitoid flies in the family Tachinidae exhibit a broad spectrum of host-specificity, with many s...

The physiological efficiency hypothesis argues that the physiological efficiency of food utilization determines feeding habits of herbivorous insects. Although relatively unsuccessful at explaining dietary specificity, it may explain the food-mixing habit of individually polyphagous herbivores because they may opportunistically increase physiologic...

While studies of tri-trophic interactions have uncovered a variety of mechanisms influencing the dietary specialization of insect herbivores, such studies have neglected host-plant selection by generalists. Here, we report an initial investigation on how host-plant quality and a tachinid parasitoid interact to affect the survival and host-plant sel...

A major goal of insect community ecology is to understand how and why herbivorous insect species vary in the diversity of their parasitoid assemblages and the rates of parasitism that they experience. Most studies investigating these issues with Lep- idoptera as hosts have relied on literature records of parasitoid-host associations that are often...

Food mixing by herbivores is thought to balance nutrient intake and possibly dilute secondary metabolites characteristic of different host plant species. Most empirical work on insect herbivores has focused on nutrient balancing in laboratory settings. In this study, we characterize food mixing behaviour of the caterpillar Grammia geneura (Strecker...

Abstract 1. Over 3400 larvae of the polyphagous ground dwelling arctiid Grammia geneura were sampled and reared over seven generations in order to characterise its parasitoid assemblage and examine how and why this assemblage varies over time and space at a variety of scales. 2. The total parasitoid assemblage of 14 species was dominated both in di...

Behavioural mechanisms of food mixing were studied in the polyphagous caterpillar Grammia geneura (Strecker) (Lepidoptera, Arctiidae) in arenas with different plant foods. Combinations of food plants, including single and multiple plant species were used. Behavioural observations on individuals of similar age were undertaken for 4 h. Foraging and f...

Polyphagy can occur at the level of species, population or individual. We analyzed foraging by two polyphagous species of caterpillar in the field and laboratory in a first investigation of the differences between polyphagy at different levels. We sought to obtain details that would in- form different regulatory mechanisms and different adaptive ba...

The use of multiple host-plant species by populations of insect herbivores can result from a variety of possible ecological and behavioral mechanisms. An understanding of the foraging mechanisms determining polyphagy in relation to local ecological conditions is therefore essential to understanding the evolutionary ecology of polyphagy. Here, we ev...

We examined the effects of desiccation on eggs and first-instar larvae of two species of Lepidoptera, Grammia geneura (Arctiidae) and Manduca sexta (Sphingidae). Grammia geneura occurs primarily in grasslands and savannas of the southwestern United States; M. sexta co-occurs with G. geneura but also is cosmopolitan across much of the Western Hemisp...

Caterpillars of the arctiid moth, Grammia geneura, are polyphagous, but species of Plantago are amongst their preferred food plants. A neuron in the medial styloconic sensillum on the galea has been shown to have a general phagostimulatory function. Experiments with binary mixtures and cross-adaptation have demonstrated that it responds to some sug...