Salvatore J. Agosta

Ecological fitting by phenotypically flexible genotypes: implications for species associations, community assembly and evolution

Ecological fitting is the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition. This paper has four major aims. First, we review the original concept of ecological fitting and relate it to the concept of exaptation and current ideas on the positive role of phenotypic plasticity in evolution. Second, we propose phenotypic plasticity, correlated trait evolution and phylogenetic conservatism as specific mechanisms behind ecological fitting. Third, we attempt to operationalize the concept of ecological fitting by providing explicit definitions for terms. From these definitions, we propose a simple conceptual model of ecological fitting. Using this model, we demonstrate the differences and similarities between ecological fitting and ecological resource tracking and illustrate the process in the context of species colonizing new areas and forming novel associations with other species. Finally, we discuss how ecological fitting can be both a precursor to evolutionary diversity or maintainer of evolutionary stasis, depending on conditions. We conclude that ecological fitting is an important concept for understanding topics ranging from the assembly of ecological communities and species associations, to biological invasions, to the evolution of biodiversity.

How Specialists Can Be Generalists: Resolving the "Parasite Paradox" and Implications for Emerging Infectious Disease

The parasite paradox arises from the dual observations that parasites (broadly construed, including phy- tophagous insects) are resource specialists with restricted host ranges, and yet shifts onto relatively unrelated hosts are common in the phylogenetic diversification of parasite lineages and directly observable in ecological time. We synthe- size the emerging solution to this paradox: phenotypic flexibility and phylogenetic conservatism in traits related to resource use, grouped under the term ecological fitting, provide substantial opportunities for rapid host switching in changing environments, in the absence of the evolution of novel host-utilization capabilities. We discuss mechanisms behind ecological fitting, its implications for defining specialists and generalists, and briefly review empirical examples of host shifts in the context of ecological fitting. We conclude that host shifts via ecological fitting provide the fuel for the expansion phase of the recently proposed oscillation hypothesis of host range and speciation, and, more generally, the generation of novel combinations of interacting species within the geographic mosaic theory of coevolution. Finally, we conclude that taxon pulses, driven by climate change and large-scale ecological perturbation are drivers of biotic mixing and resultant ecological fitting, which leads to increased rates of rapid host switching, including the agents of Emerging Infectious Disease.

Mammalian Metabolic Allometry: Do Intraspecific Variation, Phylogeny, and Regression Models Matter?

Power scaling relationships between body mass and organismal traits are fundamental to biology. Compilations of mammalian masses and basal metabolic rates date back over a century and are used both to support and to assail the universal quarter‐power scaling invoked by the metabolic theory of ecology. However, the slope of this interspecific allometry is typically estimated without accounting for intraspecific variation in body mass or phylogenetic constraints on metabolism. We returned to the original literature and culled nearly all unique measurements of body mass and basal metabolism for 695 mammal species and (1) phylogenetically corrected the data using the fullest available phylogeny, (2) applied several different regression analyses, (3) resampled regressions by drawing randomly selected species from each of the polytomies in the phylogenetic hypothesis at each iteration, and (4) ran these same analyses independently on separate clades. Overall, 95% confidence intervals of slope estimates frequently did not include 0.75, and clade‐specific slopes varied from 0.5 to 0.85, depending on the clade and regression model. Our approach reveals that the choice of analytical model has a systematic influence on the estimated allometry, but irrespective of the model applied, we find little support for a universal metabolic rate–body mass scaling relationship.

Feeding ecology of the bat Eptesicus fuscus: ‘preferred’ prey abundance as one factor influencing prey selection and diet breadth

Factors influencing prey selection by insectivorous bats are poorly understood but may be related to interspecific differences in echolocation call structure. The diet of Eptesicus fuscus was compared with prey abundance across a foraging season to examine prey selection by a bat species which has an echolocation call dominated by a frequency-modulated (FM) component. Guano samples were collected on 18 occasions from a single colony between May and September 2000. Abundance of aerial insects was measured using a black-light trap on nights when guano was collected. Regression analysis was used to test the hypotheses that E. fuscus: (1) does not take prey in proportion to their relative abundance; (2) forages preferentially for beetles in a manner predicted by foraging theory. Relative abundance (= proportion in relation to other prey types) of prey in trap samples was not a good predictor of prey in the diet across periods or within periods, which suggests selective foraging. Beetles (42–96% of the diet by per cent volume) were consistently eaten in higher proportions than their relative abundance. The absolute abundance of beetles (= abundance irrespective of the abundance of other prey types) explained 60% of the variation in beetle use with more beetles eaten when they were abundant. Absolute beetle abundance explained 66%, 53% and 47% of the variation in the use of three other prey types, with more of these prey eaten when beetle abundance was low. Finally, absolute beetle abundance explained 60% of the variation in diet breadth, which increased when beetle abundance was low. Our results agree with predictions derived from foraging theory and support the hypothesis that E. fuscus forages selectively for beetles, consuming a wider variety of prey when beetle abundance is low. These results are similar to those found for the greater horseshoe bat Rhinolophus ferrumequinum which has an echolocation call dominated by a constant-frequency (CF) component, and suggest that some FM bats may discriminate among prey taxa, at least at the ordinal level.

Phylogeny, Regression, and the Allometry of Physiological Traits

Physiological and ecological allometries often pose linear regression problems characterized by (1) noncausal, phylogenetically autocorrelated independent (x) and dependent (y) variables (characters); (2) random variation in both variables; and (3) a focus on regression slopes (allometric exponents). Remedies for the phylogenetic autocorrelation of species values (phylogenetically independent contrasts) and variance structure of the data (reduced major axis [RMA] regression) have been developed, but most functional allometries are reported as ordinary least squares (OLS) regression without use of phylogenetically independent contrasts. We simulated Brownian diffusive evolution of functionally related characters and examined the importance of regression methodologies and phylogenetic contrasts in estimating regression slopes for phylogenetically constrained data. Simulations showed that both OLS and RMA regressions exhibit serious bias in estimated regression slopes under different circumstances but that a modified orthogonal (least squares variance‐oriented residual [LSVOR]) regression was less biased than either OLS or RMA regressions. For strongly phylogenetically structured data, failure to use phylogenetic contrasts as regression data resulted in overestimation of the strength of the regression relationship and a significant increase in the variance of the slope estimate. Censoring of data sets by simulated extinction of taxa did not affect the importance of appropriate regression models or the use of phylogenetic contrasts.

Fitness consequences of host use in the field: temporal variation in performance and a life history tradeoff in the moth Rothschildia lebeau (Saturniidae)

That fitness varies as a function of using different hosts is a basic premise of theory addressing the ecology and evolution of oviposition behavior and host selection. Few data exist demonstrating: (1) the effects of different hosts on fitness in the field, and (2) how these effects vary spatially or temporally. Cohorts of caterpillars were followed from hatching to adulthood to test the hypotheses that: (1) hosts have significant effects on herbivore performance in nature, and (2) host “quality” for performance varies predictably (i.e., the rank order is consistent) across herbivore generations. In total, the fates of >2,000 caterpillars were followed on 238 individual host trees. Host species had significant effects on most, but not all, measured components of caterpillar performance in the field. Variation among generations was mainly quantitative rather than qualitative, with few changes in the rank order of hosts in their effects on performance. There was also a strong seasonal effect on performance such that caterpillar growth and survival were higher in the early wet season compared to the late wet season. Using estimates derived from these data, correlations among larval growth rate, larval survival, total development time, and final adult size were examined at the level of host plant species. Across generations, larval survival was consistently poor, development time was long, but final adult size attained was large on the host Spondias mombin. The converse was true for the host Exostema mexicanum. Relative performance on the host Casearia nitida was variable between the other two hosts. Overall, the data suggest that host use involves a predictable tradeoff between larval survival and final adult size, but argue that which is the “better” host from the female perspective will depend on the fitness consequences of producing a few, relatively large offspring versus producing more, relatively small offspring.

DIET OF THE BIG BROWN BAT, EPTESICUS FUSCUS, FROM PENNSYLVANIA AND WESTERN MARYLAND

Abstract We used fecal analysis to describe the diet of Eptesicus fuscus in Pennsylvania and western Maryland. We examined spatial variation in diet composition among three populations and temporal variation within a maternity colony. Temporal patterns of prey use were compared with similar data collected previously from a maternity colony in Indiana. Overall, Coleoptera (58–82%), especially Scarabaeidae (14–31%), were the dominant prey items. Hemiptera, primarily Acrosternum hilare (5–19%), were also major prey, and Tettigoniidae (not previously reported) were prey of two populations (6%, 17%). Significant spatial and temporal variation existed in diet composition among populations and use of major prey types, respectively. Comparison of temporal data collected in this study and in Indiana indicated a nearly identical pattern in the use of Scarabaeidae. These insects are abundant in the spring, and the data suggest widespread specialization on Scarabaeidae in April and May. Several insects preyed on by E. fuscus in this study are serious agricultural pests.

Determinants of clinal variation in life history of dusky salamanders (Desmognathus ocoee): prey abundance and ecological limits on foraging time restrict opportunities for larval growth

Recent models argue that thermal environments are the major cause of ectotherm life-history clines. However, elevational clines in body size in the mountain dusky salamander Desmognathus ocoee (family Plethodontidae) shift from positive at hatching, to negative at metamorphosis to positive again as adults, and so are not consistent with this explanation. The clinal shift from hatching to metamorphosis was investigated by examining the clinal and seasonal feeding patterns of larval salamanders at high and low elevation sites in rockface and woodland habitats. Repeated cohort sampling was also used to examine clinal and seasonal patterns in body size and to estimate average growth rates. Larval growth in both rockface and woodland habitats was tightly correlated with feeding activity. Although temperature was found to vary between high and low elevation sites, the greatest growth occurred in a cold woodland habitat with a high elevation, and the lowest growth occurred in an adjacent rockface habitat. Because this difference in growth cannot be attributed to thermal differences, we conclude that local food resource levels are the predominant source of local differences in growth. These findings, clinal patterns of variation in other predatory salamanders, and experimental analyses in which both food and temperature are orthogonally manipulated, indicate that general models that single out temperature as the principle cause of ectotherm life-history clines should be viewed with caution.

NIGHTLY, SEASONAL, AND YEARLY PATTERNS OF BAT ACTIVITY AT NIGHT ROOSTS IN THE CENTRAL APPALACHIANS

Abstract This study presents data from 2 years of extensive sampling from July to October at 7 caves and mines used by bats in the Appalachian Mountains region of western Maryland and southwestern Pennsylvania. In total, 2,860 individuals from 7 species were captured. We examined species composition at roosts and compared our data to a survey conducted at 5 of the same caves and mines 2 decades ago; roosts were used by up to 6 species, and species composition has remained stable. In addition, we examined roost fidelity via mark and recapture (at 1 cave); population structure; and nightly, seasonal, and yearly patterns of use. Bats exhibited a very low rate of recapture (2.8%). Few bats were captured exiting the roosts before or during the 1st hour after sunset; peaks in nightly captures at roosts generally occurred 3–5 h after sunset, with few differences between sex and age classes. These patterns were indicative of frequent use of these caves and mines as night roosts by large numbers of individuals. For the 4 most abundant species (Myotis lucifugus, M. septentrionalis, Pipistrellus subflavus, and Eptesicus fuscus), roosts were used by adults and juveniles of both sexes. Adult sex ratios were skewed toward males, whereas juvenile sex ratios approached 1:1 in 1 of 2 years for each species. Nightly ambient temperatures explained little of the variation in capture times (2%) or capture success (10%). For each species, seasonal patterns of activity were similar between years, but there were differences among species. Overall, bat activity was highest in late August in both years.

Alternative strategies of seed predator escape by early-germinating oaks in Asia and North America

Early germination of white oaks is widely viewed as an evolutionary strategy to escape rodent predation; yet, the mechanism by which this is accomplished is poorly understood. We report that chestnut oak Quercus montana (CO) and white oak Q. alba (WO) (from North America), and oriental cork oak Q. variabilis (OO) and Mongolian oak Q. mongolica (MO) (from Asia) can escape predation and successfully establish from only taproots. During germination in autumn, cotyledonary petioles of acorns of CO and WO elongate and push the plumule out of the cotyledons, whereas OO and MO extend only the hypocotyls and retain the plumule within the cotyledons. Experiments showed that the pruned taproots (>6 cm) of CO and WO acorns containing the plumule successfully germinated and survived, and the pruned taproots (≥12 cm) of OO and MO acorns without the plumule successfully regenerated along with the detached acorns, thus producing two seedlings. We argue that these two distinct regeneration morphologies reflect alternative strategies for escaping seed predation.