Interactions Among Top-down Regulators in a Temperate Forest Floor Ecosystem;Effects on Macrofauna, Mesofauna, Microbes and Litter Decay

High species diversity and complexity of forest-floor food webs present a challenge for understanding the role of species interactions (e.g. competition and predation) as regulatory mechanisms for ecosystem processes such as decomposition and nutrient cycling. In particular, we understand very little about the roles of forest-floor predators in regulating diversity and abundance of lower trophic levels and ecosystem processes. However, ecological theory and several studies suggest that interactions among intraguild predators (IGP) may be important controls of diversity and abundance of organisms and detritus in lower trophic levels within food webs. A key prediction is that interactions among predators weaken trophic cascades. My research examined this prediction by characterizing interactions among predators and examining their effects on lower trophic levels within the forest-floor food web of Northeast Ohio. The results of the laboratory microcosm studies, in combination with several previous studies, suggest that the effects of removal treatment on intraguild predators, especially centipedes, spiders, carabid beetles, and salamander, were not the result of intraguild predation, but were more likely to have been the result of non-consumptive competitive interactions (NCEs). Predator removal from open, unrestricted field plots resulted in changes in the abundances of several groups of predators and macrodetritivores. Additionally, I found that predator manipulation affected composition of microflora within the soils at my field site. The mechanisms for this effect remain uncertain but may be indicative of antibiotic interactions within the soil through bacteria dispersed through skin secretions and feces of predators, particularly salamanders. This work contributes significantly to a growing body of evidence indicating that territorial predators, such as P. cinereus, which are constrained to spatially fixed microhabitats, can be strong regulators of guild members and lower trophic levels. My results also supp

Behavioral interactions between terrestrial salamanders and spiders: competition or intraguild predation? Behavioral interactions between terrestrial salamanders and spiders: competition or intraguild predation?

Several studies suggest that small terrestrial salamanders are important regulators of leaf litter arthropod communities, and likely contribute to ecosystem processes such as decomposition and nutrient cycling. Despite the recognition that salamanders have the potential to strongly affect ecosystem function through both direct and indirect pathways, little is known regarding the nature of interactions between small vertebrates and the large, predatory arthropods with which they share both microhabitat and prey. Our study was designed to explore interactions between Eastern Red-backed Salamanders, Plethodon cinereus, and spiders in the genus Wadotes in an eastern North American temperate forest ecosystem. We were particularly interested in teasing apart behaviors such as territoriality and intraguild predation in an attempt to determine specifically which interaction is most likely responsible for the observed negative relationship between salamander and spider abundance at our field site. Field data indicate that P. cinereus and large syntopic spiders exhibit negative spatial associations in the microhabitat beneath cover objects, a possible indication of interspecific territoriality. In our laboratory experiments, resident salamanders displayed agonistic postures similarly toward both intruding conspecifics and spiders, suggesting that salamanders may perceive large intruding spiders as competitors. Finally, we observed no injuries to individual P. cinereus or adult spiders even though occasional chases and bites by both were recorded during the behavioral trials. We found no evidence that adults or juveniles of P. cinereus were envenomated by adult Wadotes spp., and there were no instances of intra-guild predation in this study. Multiple lines of evidence from this study, and others, suggest that the primary interaction between individuals of P. cinereus and large spiders is competitive in nature rather than predatory. We suggest that the cost associated with intraguild predation on salamanders with noxious skin secretions may preclude them from being preyed upon by spiders

Competition and Intraguild Predation Between Beetles, Pterostichus stygicus (Coleoptera: Carabidae) and Centipedes, Scolopocryptops sexspinosus (Scolopemdromorpha: Scolopocryptopidae)

Studying interactions between distantly related species is necessary to understand the complexity of food webs. Generalist predator interactions, such as intraguild predation (IGP) and competition, can alleviate predation pressure and weaken top–down control that predators have on lower trophic levels. Centipedes (Chilopoda) and carabid beetles (Coleoptera) are common deciduous forest floor generalist predators that may interact by competing for resources beneath rocks and logs on the forest floor, especially during dry periods when prey become confined to such microhabitats. We used laboratory and field studies to determine whether the carabid beetle, Pterostichus stygicus (Say), and the centipede, Scolopocryptops sexspinosus (Say) co-occur under artificial cover. Additionally, a laboratory mesocosm experiment was used to examine competi- tive interactions in intra- and interspecific trials. There was significant negative co-occurrence of beetles and centipedes beneath cover objects in the field and laboratory. Pairings of S. sexspinosus and P. stygicus within mesocosms resulted in high mortality of P. stygicus, and reciprocal but asymmetric IGP. Centipedes maintained weight within solitary, intra- and interspecific mesocosm treatments, however, beetles lost mass in all treat- ments. Scolopocryptops sexspinosus responded more favorably to intra- and interspecific competition than did P. stygicus. Analysis of the leaf litter mesofauna indicated that these predators consumed similar prey in laboratory mesocosms. Our results suggest that species with very different trophic morphology have the po- tential to compete for shared microhabitat and prey

Eastern Red-backed Salamanders Regulate Top-Down Effects in a Temperate Forest-Floor Community

Understanding the role of species interactions as regulatory mechanisms for ecosystem processes presents a challenge to ecologists working in systems with high species diversity and habitat complexity. Recent studies suggest that interactions among intraguild predators, such as terrestrial salamanders and large arthropods, might be important for the regulation of detritivores, fungivores, and perhaps detritus within terrestrial webs. A key prediction is that interactions among predators weaken trophic cascades. Our research examined this prediction by removing predators for 4 yr from unfenced field plots to investigate the effects on litter arthropods, the microbial community, and rates of leaf litter decomposition. We manipulated predator abundance in three treatments (salamander removal, centipede removal, and multiple predator removal) compared to a control in which no predators were removed. Despite difficulties in suppressing centipede numbers, we observed increases in salamanders, millipedes, isopods, slugs, numbers of ant colonies, and gamasid mites in the centipede removal plots. Additionally, several phospholipid fatty acid markers for bacteria were suppressed in plots where salamanders were most abundant. Finally, we detected treatment effects on the rate of litter disappearance from leaf bags in our field plots: those with the most salamanders had the lowest levels of litter decomposition. Overall, we found some evidence for top-down effects of predators in a temperate forest-floor web. Our study is one of few that have employed an unfenced field design and the only study examining the effects of salamanders on forest soil microbes. The results contribute to a growing body of evidence indicating that territorial predators, such as terrestrial salamanders, can be strong regulators of species composition at lower trophic levels in a system that is commonly thought to be regulated primarily through bottom-up effects of organic matter supply

Species Variation in a Pheromone Complex is Maintained at the Population Level in the Eastern Red-Backed Salamander

Protein pheromones in salamanders of the genus Plethodon have experienced rapid and pervasive directional selection. Variation in mate recognition components, such as the sex-specific pheromones used by plethodontid salamanders, may influence sexual incompatibility and therefore provide a biochemical mechanism for the maintenance of discrete, isolated populations. Recent studies suggest that multiple, genetically distinct lineages of Eastern Red-Backed Salamanders (Plethodon cinereus) are present throughout their broad range. Representative populations from two of these lineages (the Ohio [OH] and Pennsylvania [PA] clades) span the southern shore of Lake Erie in northern Ohio. This distribution pattern creates a unique opportunity to study how phenotypic differences may reinforce population boundaries and possibly lead to speciation. The objectives of this study were to 1) characterize the pheromone profiles of male P. cinereus and 2) determine pheromone variation among populations and between the OH and PA clades. The composition of proteins associated with two known courtship pheromones, Plethodontid Modulating Factor (PMF) and Plethodontid Receptivity Factor (PRF), were compared among eight populations in northern Ohio. Analyses of Similarity (ANOSIM) suggest that both PMF and PRF profiles differ among populations but not between clades. These data suggest that the sex-specific pheromones of P. cinereus in the two clades are not yet different enough to allow reproductive isolation between the two genetic lineages. Although the relative roles of selection and genetic drift are unknown in our populations, specific pheromone isoforms and their effects on mate compatibility should be the focus of future studies aiming to determine mechanisms involved in maintaining population differences

Repeatability of foraging behavior following a simulated predation attempt depends on color morph, sex, and foraging metric in Red-backed salamanders (Plethodon cinereus)

Behavioral repeatability greatly affects the capacity of an individual to respond to varying environments. When multiple behaviors within individuals are repeatable and correlated across time or across contexts, it is termed a behavioral syndrome. However, not all behaviors exhibit the same level of repeatability, and relatively few studies have examined repeatability in amphibians. We examined the repeatability of foraging behavior in the Eastern Red-backed salamander (Plethodon cinereus), a color-polymorphic terrestrial salamander, following a simulated predation attempt. We tested several hypotheses: (1) Simulated predation would negatively affect foraging, increasing latency to feed and decreasing the number of prey items eaten in a fixed time period compared to a control group; (2) Because striped color morphs of P. cinereus are more aggressive, striped individuals would exhibit “bold” behavior by resuming foraging sooner and consuming more prey; and (3) Foraging behavior would be more repeatable for males. We found that the predation treatment inhibited foraging behavior, although neither morphs nor sexes differed in either forging metric. The number of prey eaten was repeatable for all groups of salamanders. Latency to feed, however, was not repeatable for control salamanders. Simulated predation induced repeatable latencies, but when morphs and sexes were analyzed separately, only unstriped and male salamanders were repeatable, suggesting characteristics of these groups related to behavioral syndromes drive this response. We speculate that the greater repeatability of the unstriped morph’s latency to feed may result from more frequent encounters with predators in the leaf litter matrix while foraging. Striped salamanders from the source population, in turn, exhibit greater territorial success, and thus may experience more variation in encounters with predators and conspecifics over the course of their lifespans. Our results illustrate the need to carefully define the behavior and subset of the population to be tested when studying behavioral repeatability or behavioral syndromes

Male mate preference as an agent of fecundity selection in a polymorphic salamander

Color polymorphisms are associated with variation in other traits which may affect individual fitness, and these color‐trait associations are expected to contribute to nonrandom mating in polymorphic species. The red‐backed salamander (Plethodon cinereus) exhibits a polymorphism in dorsal pattern: striped and unstriped, and previous studies have suggested that they may mate nonrandomly. However, the mechanism(s) contributing to this behavior remain unclear. Here we consider the role that male preference may have in driving mating behavior in P. cinereus. We limit our focus to striped individuals because this morph is most likely to be choosy given their dominant, aggressive behavioral profiles relative to unstriped males. Specifically, we evaluated (a) whether striped males preferentially associate with females with respect to her dorsum color, size, and body condition and (b) if so, whether female traits are evaluated via visual or chemical cues. We also considered whether the frequency of another male social behavior, nose taps, was associated with matepreferences. We found that striped male P. cinereus nose tapped more often to preferred females. However, males only assessed potential mates via chemical cues, preferring larger females overall. Reproductive phenology data on a sample of gravid females drawn from the same population indicated that the color morphs do not differ in reproductive traits, but larger females have greater fecundity. Given our findings, we conclude that female P. cinereus are under fecundity selection, mediated by male preference. In this manner, male mating behavior contributes to observations of nonrandom mate associations in this population of P. cinereus

Using a comparative approach to investigate the relationship between landscape and genetic connectivity among woodland salamander population

For many amphibian species, reduced landscape connectivity results in reduced genetic connectivity among populations. However, large efective population sizes (Ne) slow the rate of genetic drift, causing subdivided populations to remain genetically similar despite little gene fow among them. Therefore, it is important to address the combined efects of Ne and matrix permeability to quantify the relative importance of gene fow and genetic drift on isolated amphibian populations. We applied a landscape genetic approach to investigate how patterns of gene fow (m), Ne (inferred via θ) and genetic difer- entiation difer among Eastern Red-backed Salamander (Plethodon cinereus) populations in a fragmented landscape (n=4) compared to a continuous forest (n=4). We assayed a panel of 10 microsatellite markers for population genetic analyses. Additionally, we constructed and validated a distribution model to generate resistance surfaces for examining the relation- ship between landscape connectivity, m, θ, and genetic diferentiation (FST) using maximum-likelihood population-efects models (MLPE). Populations in continuous habitat were undiferentiated, whereas fragmented populations exhibited genetic structure driven by a single population. Results of the MLPE models in the fragmented landscape revealed spatial variation in θ as the best predictor of pairwise FST, followed by estimates of m, suggesting migration-drift interactions have a stronger infuence on genetic diferentiation than matrix permeability. Moreover, model coefcients for landscape resistance were comparable between landscapes. Overall, our results provide insight as to how the interaction of gene fow and genetic drift shapes population structure for a dispersal-limited species within a predominately anthropogenic landscape