Robert T. M'Closkey

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.

Community Structure in Sympatric Rodents

Species diversity, microhabitat separation, microhabitat shifts and body size patterns are examined in seven sympatric rodent species. Habitat separation and seasonal shifts are identified by multiple-group discriminant analysis on microhabitat variables repre- senting shrub structure and substrate patchiness. The rodents form two functional groups. Four permanent, year-round residents (Pero- mnyscus eremicus, Neotoma lepida, Neotoma fuscipes, and Dipodomys agilis) show significant separation on habitat structure and some temporal habitat shifts. Three seasonal residents (Peromyscus maniculatus, Peromyscus californicus, and Reithrodontomys megalotis) show no microhabitat shifts and have a greater frequency of microhabitat overlap with one another and with permanent residents. There is no relationship between niche breadth and population density for any given species; however, as a group, seasonal residents show reduced breadth with increased popula- tion density. The significance of this pattern is discussed with respect to ecological opportunism of seasonal residents. The pattern of body size differences within the fauna is examined in light of habitat structure. Pairwise differences in habitat structure and body size are positively correlated. The data show that permanent residents are more different from one another in body size and structural habitat than pairs in which at least one species is a seasonal resident. Increased similarity in body size and microhabitat structure may not favor year-round coexistence in some pairs of species. The most similar-sized pair of species are congeneric deer mice (P. eremnicus and P. inaniculatus), and in addition to seasonal separation, they show niche dif- ference by habitat structure.

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.

Ecological Separation of Sympatric Rodents (Peromyscus and Microtus)

This paper quantifies the ecological separation of locally sympatric Peromyscus leucopus and Microtus pennsylvanicus . Major niche dimensions examined were food, arboreal habitat, and overall structural habitat. Diet overlap was low and arboreal activity of Peromyscus was independent of Microtus presence or absence. Significant structural habitat separation was identified by discriminant function analysis and was due to differences in foliage profile diversity, tree density, and depth of the mat of perennial grass.

Determinants of Local Distribution and Abundance in White‐Footed Mice

To establish plausible explanations of the factors determining patterns of local distribution and abundance of white-footed mice, Peromyscus leucopus, concurrent measures of habitat structure, plant species composition, and mouse density were performed in several seral stages at Point Pelee National Park, southern Ontario. Population density covaries with foliage profile structure among habitats in which P. leucopus occur, whereas floristic com- position is unimportant. White-footed mouse distribution and restriction to nongrassland habitats may be due to a significant structural difference between grassland and nongrassland habitats.

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.

Habitat Dimensions of White-footed Mice, Peromyscus leucopus

Analysis of arboreal components of two habitats of white- footed mice (Peromyscus leucopus) revealed that use of the components (branch height, angle and diameter) was proportional to their occur- rence. Frequency of mouse activity, monitored in 8 m3 volumes of habi- tat, was correlated with measurements of habitat structure which described the configuration of branches in the habitat. Only two plant species (Rhus typhina and Vitis riparia) were significantly associated with P. leucopus habitat use.

Lizard microhabitat and fire fuel management

Abstract For many species, dead vegetation is important microhabitat necessary for survival and reproduction. We compared the use of three categories of trees: living, dead standing and dead prone, within and among four species of phrynosomatid lizard (Sceloporus undulatus, Sceloporus graciosus, Urosaurus ornatus, and Uta stansburiana) on the Colorado Plateau during 1990, 1992 and 2000. All four species used dead trees (both prone and standing) more frequently than live trees, despite an opposite pattern of availability. U. ornatus used dead standing more often than dead prone trees, reflecting this lizards arboreal nature. Tree use did not differ among lizard species, and the lizard species by tree category interaction was not significant. Current policy mandates the removal of dead vegetation and debris on US Federal lands as basic maintenance in order to decrease fire risk. Active removal of “fuel” may limit the local distribution, abundance, and diversity of these lizards, which include dead trees in their microhabitat for shelter, perching, foraging, courting, and defending territories.

Defense of mates: a territory departure rule for male tree lizards following sex-ratio manipulation

SummaryMale tree lizards (Urosaurus ornatus) abandon their territories following the removal of potential mates. Departure time averages 25 days but varies from 1 to 7 weeks. We show that most of the variation (r2=0.78) in departure of males can be accounted for by the number of females removed from male territories and adjacent trees. Males occupying higher quality territories (more potential mates) have short departure times, whereas males on poorer territories (fewer fameles) stay longer after female removal. We hypothesize that the inverse relationship between male departure time and the number of females removed from their territories is a consequence of the males previous expectation of envountering prospective mates. In addition, experimental introduction of non-resident males into the territories of resident males revealed the inability of intruder males to become established on occupied territories.

SPATIAL PATTERNS IN SIZES OF SEEDS COLLECTED BY FOUR SPECIES OF HETEROMYID RODENTS

This research was designed to provide information on the spatial variation in size of seeds collected by four species of heteromyid rodents. During summer 1975, rodents (Dipodomys merriami, Perognathus amplus, P. baileyi, and P. penicillatus) were live-trapped on several Sonoran Desert habitats at the Saguaro National Monument in southern Arizona, USA. In 1976 and 1977 a single study area containing all four rodent species was live-trapped to provide information on mi- crohabitat and seed use among coexisting species. Any seeds contained in the cheek pouches of the rodents were identified and their linear dimensions were measured. Microhabitats were quantified by enumeration of shrubs and measurement of their size. Much of the variation in collection of different-sized seeds is attributable to habitat and micro- habitat differences between rodent species. Not only do rodent species collect seeds of different size among different habitats, but within a habitat, locally coexisting rodent species collect seeds of different size. As a test of the concept of independent use of two resources (seed size and microhabitat) by coexisting species, seed size differences were compared to microhabitat differences between all pairs of heteromyid rodents. The results show that the difference between rodent species in the size of seeds they collect depends upon the difference in microhabitat selection of the species. Hence, these two components of the niche (seed size and microhabitat) of coexisting heteromyid rodents reduce to a single dimension.