Stephen J. Hecnar

The effects of predatory fish on amphibian species richness and distribution

Abstract Amphibian communities at 178 ponds across southwestern Ontario, Canada, were studied to determine if presence of predatory fish was related to altered amphibian species richness or distribution on a geographic scale. Ponds are an important amphibian habitat in the study area and many have been stocked with fish. Surveys conducted over three years were used to construct amphibian species lists for individual ponds. Species richness and presence/absence were compared among ponds classified by the type of fish present. Amphibian species richness was significantly lower at ponds having predatory fish present than at non-predatory, or fish-free, ponds. Not all amphibian species were negatively affected by the presence of predatory fish: those having either large bodies or clutch size co-occurred with predatory fish more frequently than those with small bodies or clutch size. Introduction of predatory fish by humans has likely resulted in altered amphibian species assemblages and reduced community diversity on a geographic scale.

Patterns of nestedness and species association in a pond-dwelling amphibian fauna

The pattern of nested species subsets has been reported for many taxa in naturally or anthropogenically fragmented habitats. Of continued interest to ecologists is whether nestedness is more frequently and strongly associated with either selective extinction or selective colon, We studied patterns of amphibian incidence at 118 ponds in southwestern Ontario from 1992 to 1994. Our objectives were to determine if individual species, groups of species, or the entire fauna was nested, and at what spatial scale, to examine patterns of species association, and to evaluate causal hypotheses. The entire fauna was signiticantly nested at the geographic. region and sub-region scales. Most species were highly nested, but differences occurred among regions for some species. Species grouped by their requirement for woodland habitat or susceptibility to fish predation showed a high degree of nestedness. Historic deforestation and introduction of predatory, fish are the likely mechanisms of extinction in this fauna. Species grouped as good dispersers were less nested than spoor disperse. Species incidence was positively correlated with potential dispersal abilities. Our results suggest the importance of both selective extinction and selective colonization in contributing to the degree of nestedness in this fauna. Nested patterns may be the rule for faunas having high turnover on mainlands. Species poor sites were dominated by the same assemblage of three species, suggesting that single large reserves are preferable to several small reserves for conservation of temperate zone pond-dwelling amphibian assemblages.

Accessible habitat: an improved measure of the effects of habitat loss and roads on wildlife populations

Habitat loss is known to be the main cause of the current global decline in biodiversity, and roads are thought to affect the persistence of many species by restricting movement between habitat patches. However, measuring the effects of roads and habitat loss separately means that the configuration of habitat relative to roads is not considered. We present a new measure of the combined effects of roads and habitat amount: accessible habitat. We define accessible habitat as the amount of habitat that can be reached from a focal habitat patch without crossing a road, and make available a GIS tool to calculate accessible habitat. We hypothesize that accessible habitat will be the best predictor of the effects of habitat loss and roads for any species for which roads are a major barrier to movement. We conducted a case study of the utility of the accessible habitat concept using a data set of anuran species richness from 27 ponds near a motorway. We defined habitat as forest in this example. We found that accessible habitat was not only a better predictor of species richness than total habitat in the landscape or distance to the motorway, but also that by failing to consider accessible habitat we would have incorrectly concluded that there was no effect of habitat amount on species richness.

Changes in the composition of a ranid frog community following bullfrog extinction

-Natural experiments have often shown that lowered competition or predation results in patterns of ecological release, density compensation, or predatory release of target species. At Point Pelee National Park, Ontario, Canada, from 1992 to 1994, we conducted extensive surveys of habitats to document patterns of relative abundance and distribution of amphibians and to compare these patterns with those documented in studies conducted in 1972 and 1991. Bullfrogs (Rana catesbeiana) have not been observed since spring 1990 and are now considered to be locally extinct in the park. Relative abundance of the green frog (R clamitans) has increased 4X since bullfrog extinction. Similarities in the natural history of bullfrogs and green frogs suggest that interactions should be greatest between this pair. The predaceous habits of bullfrogs are well-documented, and the experimental literature suggests that bullfrogs and green frogs are competitors. Changes in the pattern of ranid relative abundance that we observed suggest that the bullfrog is important in structuring amphibian communities.

Effects of human disturbance on five-lined skink, Eumeces fasciatus, abundance and distribution

We studied the effects of human disturbance on five-lined skinks at Point Pelee National Park, Canada. Surveys indicated low skink abundance and a lack of woody debris in areas heavily used by humans and a downward population trend concurrent with high disturbance levels. Skinks preferentially used large moderately decayed logs and boards for refuge sites. Human disturbance resulted in degradation and removal of debris. Degradation by fragmentation and accelerated decay resulted in decreased quality of available debris. To test the hypothesis that skink absence in human high-use areas was caused by a lack of suitable debris, we placed artificial microhabitats in areas which previously lacked woody debris and skinks. Experimental debris were colonized quickly and heavily used despite high disturbance rates. Skinks are resilient to minor disturbances such as displacements, but not to removal or degradation of debris. Essential microhabitat features must be actively preserved as well as suitable habitat to ensure the conservation of target species.

Trap Response and Genetic Structure of Eastern Subterranean Termites (Isoptera: Rhinotermitidae) in Point Pelee National Park, Ontario, Canada

Abstract Reticulitermes flavipes (Kollar) is best known throughout southwestern counties of Ontario, Canada, as an urban pest. Little is known, however, of the presence of this termite in nonurban settings in Ontario. In this study, we confirmed the existence of a population of R. flavipes on the shores of Lake Erie within Point Pelee National Park. A systematic trap survey conducted along the parks semi-vegetated west beach revealed several zones of termite activity. An analysis of trap response at one location indicated an association between termite activity and smaller sized, moderately decayed woody debris. Further, microsatellite DNA analysis suggested the presence of at least three genetically distinct colonies, each likely headed by multiple inbred reproductives. Together these data suggest that termite activity is linked to food quality, and that single colonies are potentially long-lived through multiple generations of inbreeding. Assuming it is derived from a population reported from Point Pelee in 1929, the study population is the oldest known eastern subterranean termite population in Ontario.

Size distributions and sex ratios of colonizing lizards

Abstract This paper reports the body size distributions and sex ratios of four species of phyrnosomatid lizard that colonized experimentally created density sinks. The experiments were conducted in western Colorado in 1992, and lizards colonizing the habitats in 1993 were compared to those removed in 1992 and those present in 1991. Lizards colonizing the density sinks were able to disperse from adjacent habitat. For two of the species (Urosaurus ornatus and Sceloporus undulatus), colonizing lizards were significantly smaller than either those removed in 1992 or those present in 1991. Two other species (S. graciosus and Uta stansburiana) showed no difference in the size distribution of colonizing and removed lizards. In addition, sex ratios of colonizing lizards did not differ from those removed in 1992 or present in 1991. The results of the experiments have implications for the dynamics of the target populations, rescue of local populations from extinction, the regional persistence of populations subject to turnover in patchy environments, and priority effects in colonization.

Effects of Lampricide on Olfaction and Behavior in Young-of-the-Year Lake Sturgeon (Acipenser fulvescens)

The lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), is a primary component to sea lamprey control in the Laurentian Great Lakes. Though the lethal effects of TFM are well-known, the sublethal effects on fishes are virtually unknown. Here we studied the effects of TFM on the olfactory capabilities and behavior of young-of-the-year (YOY) lake sturgeon (Acipenser fulvescens). At ecologically relevant concentrations of TFM there was reduced olfactory response to all three cues (l-alanine, taurocholic acid, food cue) tested, suggesting that TFM inhibits both olfactory sensory neurons tested. Sturgeon exposed to TFM also showed a reduced attraction to the scent of food and reduced consumption of food relative to unexposed fish. Exposed fish were more active than control fish, but with slower acceleration. Fish were able to detect the scent of TFM, but failed to avoid it in behavioral trials. The connection between neurophysiological and behavioral changes, and the commonality of habitats between sturgeon and lamprey ammocoetes, suggests that there may be effects at the ecosystem level in streams that undergo lamprey control treatments.

Colonization and saturation of habitats by lizards

We studied the colonization of habitats by four species of iguanid lizard (Urosaurus ornatus, Sceloporus graciosus, S. undulatus, and Uta stansburiana) to determine differences among the species in colonization, differences among habitat types in colonization, and the time trajectory of colonization. We surveyed lizards on eight study plots in three habitats after a density reduction experiment. We discovered no difference among lizard species in their recovery relative to numbers removed. However, there were significant differences in recovery among habitats, suggesting an important role of habitat type in the resilience of the lizards to the perturbation. Colonization by lizards was rapid and most study plots were colonized within 2 to 3 mo of the manipulation. One year after the experiment, all species were represented on all plots. Saturation (ratio of marked lizards to the number removed on each plot) was significantly different between the first and all other post-manipulation census periods. There was no significant difference in saturation among the second (1 yr), third (15 mo) and fourth (27 mo) census periods, suggesting asymptotic saturation within 1 yr of the perturbation. The pattern of colonization by resident lizards was similar to that of all lizards (residents and transients). There was no difference in saturation among species, but there were significant habitat and census period differences in saturation.

Interspecific Spatial Overlap

Interspecific spatial overlap profiles are constructed for several pairs of iguanid lizard species. The profiles depict the proportion of activity points within the territories and home ranges of target lizards that are shared with individuals of other lizard species. Results show that within populations some individuals may incur little or no spatial overlap from other lizard species, whereas others have high spatial overlap. These patterns of overlap may be sustained through entire seasons of lizard activity. Profile shapes included distributions that were unimodal and strongly skewed, bimodal, and uniform with roughly equivalent proportions of low, intermediate, and high overlaps. Spatial overlap profiles are idiosyncratic, neither characterizing a particular pair of lizard species, nor typifying a specific habitat type. The observations provide insight into the results of experimental studies that show weak or undetectable effects of competition at the population level, but may include asymmetric effects targeted at specific individuals. In addition, because spatial overlap profiles for a pair of species are variable, interactions cannot be characterized by the results of an experimental manipulation conducted in just one habitat.