Epigenetic Variation May Compensate for Decreased Genetic Variation with Introductions: A Case Study Using House Sparrows (Passer domesticus) on Two Continents

Epigenetic mechanisms impact several phenotypic traits and may be important for ecology and evolution. The introduced house sparrow (Passer domesticus) exhibits extensive phenotypic variation among and within populations. We screened methylation in populations from Kenya and Florida to determine if methylation varied among populations, varied with introduction history (Kenyan invasion <50 years old, Florida invasion ~150 years old), and could potentially compensate for decrease genetic variation with introductions. While recent literature has speculated on the importance of epigenetic effects for biological invasions, this is the first such study among wild vertebrates. Methylation was more frequent in Nairobi, and outlier loci suggest that populations may be differentiated. Methylation diversity was similar between populations, in spite of known lower genetic diversity in Nairobi, which suggests that epigenetic variation may compensate for decreased genetic diversity as a source of phenotypic variation during introduction. Our results suggest that methylation differences may be common among house sparrows, but research is needed to discern whether methylation impacts phenotypic variation

Effects of Fragmentation on the Richness of Vertebrates in the Florida Scrub Habitat

Structures of habitat fragments interact with autecologies of resident species to produce patterns in taxonomic richness. Understanding this interaction is crucial to habitat conservation. We studied the vertebrates inhabiting fragments of the severely threatened sand pine scrub habitat of interior peninsular Florida. We surveyed 16 scrubs in south—central Florida that were categorized as either “large,” “medium,” or “small.” For each scrub, we determined (1) vegetational structure, (2) vegetational composition, (3) distance to the nearest scrub, (4) distance to the nearest larger scrub, (5) presence/absence of potential “corridor“ habitats between scrubs, (6) types of habitats between scrubs, (7) distance to the nearest permanent water, (8) percent coverage of surrounding habitats, and (9) area reduction over time. The principal methods used to census nonavian taxa were pitfall and double—ended funnel traps, while the principal method for avian taxa was transect surveys. Many of the nine scrub attributes were intercorrelated. Scrub size was the only attribute that correlated strongly with vertebrate richness. Distance, both to permanent water and to the nearest scrub, correlated strongly with nonavian richness after the influence of size was removed, however. We detected significant nestedness, but when the taxon—area relationship was taken into consideration, we could not demonstrate that any taxa were excluded from small scrubs. We constructed joint lists of taxa from various hypothetical “archipelagos” of the 16 individual scrubs, and found that the archipelagos often supported more taxa than large individual scrubs. We found no tendency for small scrubs to be depauperate, in general, and no matter how rare taxa were identified, they were more common than expected in medium and small scrubs, and less common than expected in large scrubs. The mere observation of either a taxon—area relationship or a nested taxonomic composition reveals little about underlying ecological processes. Our detailed analysis leads us to conclude that no evidence indicates the need for single large scrub reserves for resident vertebrates: an archipelago of individually smaller reserves could support at least as many taxa. This conclusion is based solely on the simple presence—absence of taxa in scrubs that were treated as replicates within size categories, however, and consideration of the abundances and distributions of individual taxa, and of the variation among scrubs of similar size, may lead to a different conclusion

Studying a Species in Decline: Changes in Populations of the Gopher Tortoise on Federal Lands in Florida

In 1987-88, 14 populations of the gopher tortoise, Gopherus polyphemus (Daudin), residing on federal lands in Florida were surveyed. These populations had been surveyed in 1978 79. For the five lands for which surveys could he compared, it was found that the percent of burrows that were active increased on one of the lands, decreased on another, and remained about the same on the other three. No systematic differences in size distributions between surveys were correlated with the changes in the percent of burrows that were active. For two sites that were sampled completely, Everglades National Park and J.N. Ding Darling National Wildlife Refuge, the data permitted a more precise evaluation of the differences in size distributions between surveys. This evaluation clearly illustrated that substantial, and potentially detrimental, changes in population structure have taken place on at least one federal land. Because at least one population appeared to have declined, residence on protected land cannot be assumed to assure the continued existence of a population. It follows that gopher tortoise populations even on reserves need continuous monitoring and management to prevent their decline

Studying a Species in Decline: Changes in Populations of the Gopher Tortoise on Federal Lands in Florida

In 1987-88, 14 populations of the gopher tortoise, Gopherus polyphemus (Daudin), residing on federal lands in Florida were surveyed. These populations had been surveyed in 1978 79. For the five lands for which surveys could he compared, it was found that the percent of burrows that were active increased on one of the lands, decreased on another, and remained about the same on the other three. No systematic differences in size distributions between surveys were correlated with the changes in the percent of burrows that were active. For two sites that were sampled completely, Everglades National Park and J.N. Ding Darling National Wildlife Refuge, the data permitted a more precise evaluation of the differences in size distributions between surveys. This evaluation clearly illustrated that substantial, and potentially detrimental, changes in population structure have taken place on at least one federal land. Because at least one population appeared to have declined, residence on protected land cannot be assumed to assure the continued existence of a population. It follows that gopher tortoise populations even on reserves need continuous monitoring and management to prevent their decline

Use of Experimental Enclosures to Examine Foraging Success in Water Snakes: a Case Study

Vegetation structure is an important component of habitat that may affect the outcome of a predator-prey interaction. Studies of fish have focused on how habitat structure affects a predator\u27s ability to capture prey (Crowder and Cooper, 1982; Savino and Stein, 1982; Nelson and Bonsdorff, 1990). Collectively, the results indicate either that thresholds of structural complexity exist, below or above which predation rates are hindered (Nelson, 1979; Heck and Orth, 1980), or that prey capture rate decreases monotonically as habitat complexity increases (Nelson and Bonsdorff, 1990). Generally, a stable supply of prey is available in habitats of optimal complexity, where foraging success (prey captured per unit time) is highest (Royama, 1970; Heck and Crowder, 1991). Foraging behavior may change from that of an ambush predator in densevegetation to that of active pursuit in lower vegetation densities in order to maintain a constant capture rate (Savino and Stein, 1982). Here, we present a protocol for experimentally examining the effects of varying structural complexity on predator-prey interactions using a snake as the predator. We test our methods by observing the mangrove salt marsh snake, Nerodia clarkii conlpressicauda (Lawson et al., 1991), foraging in an environment which simulates field conditions