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Glenn A. Marvin

Bio: Glenn A. Marvin is an academic researcher from University of North Alabama. The author has contributed to research in topics: Salamander & Autotomy. The author has an hindex of 4, co-authored 8 publications receiving 74 citations.

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Journal ArticleDOI
TL;DR: Competitive interactions among widely sympatric species of terrestrial plethodontid salamanders have received little attention and intense aggression (bite-holds) occurred more often during pairings between conspecifics, indicating that interference competition is greater among individuals of the same species.
Abstract: Competitive interactions among widely sympatric species of terrestrial plethodontid salamanders have received little attention. I investigated whether interspecific interference competition for space occurs between one such pair of species, Plethodon kentucki and P. glutinosus. Encounters between heterospecific adults in the laboratory resulted in aggressive interactions as often as did encounters between conspecific adults. However, intense aggression (bite-holds) occurred more often during pairings between conspecifics, indicating that interference competition is greater among individuals of the same species. Plethodon glutinosus was dominant more often than P. kentucki during encounters with heterospecifics in the laboratory. During a second laboratory experiment, both species preferentially used large cover sites in single-species control groups, whereas P. kentucki used small cover sites significantly more often in mixed-species experimental groups, indicating competitive exclusion of P. kentucki by ...

38 citations

Journal ArticleDOI
TL;DR: It is shown that tail autotomy often results in a reduction in maximal swimming performance and thus a locomotor cost for individuals of this species.
Abstract: Although tail autotomy often has an immediate survival benefit, tail loss may subsequently hinder locomotion and the ability to escape from predators. Maximal locomotor performance can be reduced after tail autotomy in the plethodontid salamander Desmognathus quadramaculatus. The loss of a large proportion of the tail length (>60%) is costly for this semiaquatic species in terms of a reduction in maximal swimming performance (i.e., burst speed is about 50% less after such autotomy). However, the minimal amount of tail loss that causes a significant reduction in swimming performance (i.e., the ''critical tail autotomy'' for locomotion) is unknown. I examined the effect of partial tail loss (either 15% or 30% of tail length) on burst swimming performance. After the loss of about 15% of tail length in one experimental group (N = 15), burst speeds for individuals were not significantly different from preautotomy burst speeds. After the loss of about 30% of tail length in a second experimental group (N = 15), burst speeds for individuals were significantly less than preautotomy burst speeds. These results indicate that the critical tail autotomy for reduction of maximal swimming performance is between 15% and 30% of tail length. About 50% of individuals in the field (N = 69) experienced tail autotomy and most (80%) of these individuals lost more than 30% of their tails. This study shows that tail autotomy often results in a reduction in maximal swimming performance and thus a locomotor cost for individuals of this species.

17 citations

Journal ArticleDOI
TL;DR: The cost of salamander tail autotomy differs among seasons and environments based on variation in temperature and food availability, and the large thermal effect resulted of delayed initiation of tail-length re-growth and reduced regeneration rate thereafter at low temperature.

9 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the locomotor cost of tail loss is greater for larger individuals of D. quadramaculatus, and this may be related to a lower propensity for caudal autotomy and a greater propensity for alternative antipredator mechanisms for such individuals.
Abstract: I examined the effect of body size on the locomotor cost of caudal autotomy in the plethodontid salamander Desmognathus quadramaculatus. In this primarily aquatic species, larger individuals autotomize the tail less readily than smaller individuals, and this may be related to a greater locomotor cost of tail loss for larger individuals. To determine whether the rate of regeneration for tail length and the recovery of maximal locomotor performance after caudal autotomy vary with body size, I measured the rate of tail re-growth and the swimming burst speed for 14 individuals (snout-vent length = 42-106 mm) as they regenerated their tails. Burst speeds of individuals were significantly reduced after caudal autotomy. With the loss of about 62% of tail length, mean burst speed declined about 50%. Thus, caudal autotomy was costly in terms of a reduction in maximal locomotor performance in an aquatic environment. After the regeneration of 50% of the tail length that was lost, post-autotomy swimming speeds were not significantly different from pre-autotomy swimming speeds. The time required for this amount of tail length regeneration (about 63-143 d) increased significantly with body size. The rate of re-growth for the lost tail length declined significantly after the regeneration of 50% of tail length. These results demonstrate that the locomotor cost of tail loss is greater for larger individuals of D. quadramaculatus, and this may be related to a lower propensity for caudal autotomy and a greater propensity for alternative antipredator mechanisms (e.g., biting) for such individuals.

8 citations

Journal ArticleDOI
TL;DR: It is concluded that most individuals of D. conanti can feed, digest, and maintain body mass for several months at constant low temperature down to 4°C, which support a growing body of data that indicate some plethodontid salamanders may acquire energy at environmental temperatures only a few degrees above freezing.

6 citations


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Journal ArticleDOI
TL;DR: It is suggested that interspecific aggression may have caused character displacement in wing spot size of Calopteryx splendens, because the intensity of aggression towards large‐spotted males is likely to increase with relative abundance of C. virgo males.
Abstract: Problems in species recognition are thought to affect the evolution of secondary sexual characters mainly through avoidance of maladaptive hybridization. Another, but much less studied avenue for the evolution of sexual characters due to species recognition problems is through interspecific aggression. In the damselfly, Calopteryx splendens, males have pigmented wing spots as a sexual character. Large-spotted males resemble males of another species, Calopteryx virgo, causing potential problems in species recognition. In this study, we investigate whether there is character displacement in wing spot size and whether interspecific aggression could cause this pattern. We found first that wing spot size of C. splendens in populations decreased with increasing relative abundance of C. virgo. Secondly, C. virgo males were more aggressive towards large- than small-spotted C. splendens males. Thirdly, in interspecific contests C. virgo males had better territory holding ability than C. splendens males. These results suggest that interspecific aggression may have caused character displacement in wing spot size of C. splendens, because the intensity of aggression towards large-spotted males is likely to increase with relative abundance of C. virgo males. Thus, interspecific aggression may be an evolutionarily significant force that is able to cause divergence in secondary sexual characters.

154 citations

Journal ArticleDOI
TL;DR: After arguing that agonistic character displacement (ACD) theory provides the most suitable theoretical framework, new empirical evidence for ACD is reviewed and the results of mathematical models of the process are reviewed.
Abstract: Competition has always been a cornerstone of evolutionary biology, and aggression is the predominant form of direct competition in animals, but the evolutionary effects of aggression between species are curiously understudied. Only in the past few years, existing theoretical frameworks have been extended to include interspecific aggression, and significant empirical advances have been made. After arguing that agonistic character displacement (ACD) theory provides the most suitable theoretical framework, we review new empirical evidence for ACD and the results of mathematical models of the process. We consider how ACD can be distinguished empirically from ecological and reproductive character displacement and the additional challenges posed by developmental plasticity. We also provide the first taxonomically broad review of theoretical and empirical work on the effects of interspecific aggression on species coexistence and range limits. We conclude by highlighting promising directions for future research on the evolutionary effects of interspecific aggression.

127 citations

Journal ArticleDOI
TL;DR: The findings of this study indicate that moisture levels and cover object availability are both significant factors in regulating abun- dances of terrestrial salamanders, but that different species and different age-classes of the same species can vary in their responses to these factors.
Abstract: I evaluated how the abundances of two species of forest-dwelling plethodontid salamanders, Plethodon cinereus and P glutinosus, are related to moisture level and availability of cover by manipulating moisture levels and cover object density on experimental plots. I also investigated how cover and moisture influence the physical condition and activity level of the most common of the two species, P cinereus. The experiment was a 2 x 2 factorial design in which plots had either low or high densities of cover objects (rocks, logs, and coarse woody debris) and were either watered by sprinklers two to three times weekly or received no supplemental watering. Nocturnal searches of the plots revealed that watering increased the abundance of juvenile R cinereus, and increased the activity levels of both juveniles and adults. Increased densities of cover objects resulted in increased abundance of both adult and juvenile P cinereus. Plethodon glutinosus was more abundant on watered plots and on plots with high densities of cover objects than on unwatered plots and plots with low densities of cover objects. The P cinereus on plots with high densities of cover objects were of higher mass, adjusted for body length and tail length, than conspecifics on plots with low densities of cover objects. This suggests that the foraging success of terrestrial salamanders is dependent on cover object availability. The findings of this study indicate that moisture levels and cover object availability are both significant factors in regulating abun- dances of terrestrial salamanders, but that different species and different age-classes of the same species can vary in their responses to these factors.

126 citations

Journal ArticleDOI
TL;DR: It is concluded that direct agonistic encounters between individuals of different species strongly influence habitat use by lizards within this assemblage of broadly sympatric species of viviparous montane skinks.
Abstract: Direct interference competition between sympatric taxa affects habitat use and shelter-site selection in species within most major vertebrate lineages. However, studies on interspecific social interference in reptiles largely have been confined to research on interactions between non-native (invasive) species and native fauna. Does interspecific interference also influence habitat use within natural assemblages of reptiles? We studied five broadly sympatric species of viviparous montane skinks within the genera Egernia and Eulamprus in southeastern Australia. Previous work has shown strong interspecific overlap in abiotic attributes of shelter-sites for these taxa, but no joint occupancy of retreats. Laboratory trials in which we manipulated the identity of co-occurring lizards revealed frequent displacement from “preferred” (hotter) shelters, with interspecific interactions more intense than intraspecific conflicts. The five species displayed a linear interspecific dominance hierarchy, with larger species displacing smaller taxa. Field manipulations confirmed that interspecific interactions between these species affect shelter-site use. We conclude that direct agonistic encounters between individuals of different species strongly influence habitat use by lizards within this assemblage.

90 citations

Journal ArticleDOI
01 Mar 2012-Ecology
TL;DR: The Noisy Miner may be the first species to have been shown to influence whole-of-avifauna assemblage structure through despotic aggressiveness over subcontinental scales and flow on to alter species abundance distributions of entire assemblages over much of eastern Australia.
Abstract: Some species have disproportionate influence on assemblage structure, given their numbers or biomass. Most examples of such "strong interactors'' come from small-scale experiments or from observations of the effects of invasive species. There is evidence that entire avian assemblages in open woodlands can be influenced strongly by individual species over very large areas in eastern Australia, with small-bodied species ( 2000 km). A series of linked Bayesian models was used to identify large-bodied (>= 50 g) bird species that were associated with changes in occurrence and abundance of small-bodied species. One native species, the Noisy Miner (Manorina melanocephala; family Meliphagidae), was objectively identified as the sole large-bodied species having similar detrimental effects in all districts, depressing occurrence of 57 of 71 small-bodied species. Adverse effects on abundances of small-bodied species were profound when the Noisy Miner occurred with mean site abundances >= 1.6 birds/2 ha. The Noisy Miner may be the first species to have been shown to influence whole-of-avifauna assemblage structure through despotic aggressiveness over subcontinental scales. These substantial shifts in occurrence rates and abundances of small-bodied species flow on to alter species abundance distributions of entire assemblages over much of eastern Australia.

78 citations