Daniel U. Greene

Invasion facilitates hybridization with introgression in the Rattus rattus species complex

Biological invasions result in novel species interactions, which can have significant evolutionary impacts on both native and invading taxa. One evolutionary concern with invasions is hybridization among lineages that were previously isolated, but make secondary contact in their invaded range(s). Black rats, consisting of several morphologically very similar but genetically distinct taxa that collectively have invaded six continents, are arguably the most successful mammalian invaders on the planet. We used mitochondrial cytochrome b sequences, two nuclear gene sequences (Atp5a1 and DHFR) and nine microsatellite loci to examine the distribution of three invasive black rat lineages (Rattus tanezumi, Rattus rattus I and R. rattus IV) in the United States and Asia and to determine the extent of hybridization among these taxa. Our analyses revealed two mitochondrial lineages that have spread to multiple continents, including a previously undiscovered population of R. tanezumi in the south‐eastern United States, whereas the third lineage (R. rattus IV) appears to be confined to Southeast Asia. Analyses of nuclear DNA (both sequences and microsatellites) suggested significant hybridization is occurring among R. tanezumi and R. rattus I in the United States and also suggest hybridization between R. tanezumi and R. rattus IV in Asia, although further sampling of the latter species pair in Asia is required. Furthermore, microsatellite analyses suggest unidirectional introgression from both R. rattus I and R. rattus IV into R. tanezumi. Within the United States, introgression appears to be occurring to such a pronounced extent that we were unable to detect any nuclear genetic signal for R. tanezumi, and a similar pattern was detected in Asia.

Integrated models that unite local and regional data reveal larger-scale environmental relationships and improve predictions of species distributions

ContextThe scale of environmental relationships is often inferred through the use of species distribution models. Yet such models are frequently developed at two distinct scales. Coarse-scale models typically use information-poor (e.g., presence-only) data to predict relative distributions across geographic ranges, whereas fine-scale models often use richer information (e.g., presence–absence data) to predict distributions at local to landscape scales.ObjectivesWe unite presence–absence and presence-only data to predict occurrence of species, what we refer to as integrated distribution models. We determine if integrated models improve predictions of species distributions and identification of characteristic spatial scales of environmental relationships relative to presence–absence modeling and ensemble modeling that averages predictions from separate presence-only and presence–absence models.MethodsWe apply recent advances in integrated distribution models to predict Sherman’s fox squirrel (Sciurus niger shermani) distribution in north-central Florida. Presence-only data were collected through a citizen-science program across its geographic range, while presence–absence data were collected using camera trapping surveys across 40 landscapes.ResultsIntegrated models estimated environmental relationships with greater precision and identified larger characteristic scales for environmental relationships than using presence–absence data alone. In addition, integrated models tended to have greater predictive performance, which was more robust to the amount of presence–absence and presence-only data used in modeling, than presence–absence and ensemble models.ConclusionsIntegrated distribution models hold much potential for improving our understanding of environmental relationships, the scales at which environmental relationships operate, and providing more accurate predictions of species distributions. Many avenues exist for further advancement of these modeling approaches.

A Comparison of Four Survey Methods for Detecting Fox Squirrels in the Southeastern United States

Abstract Fox squirrel Sciurus niger populations in the southeastern United States appear to have declined, and 3 (S. n. cinereus, S. n. shermani, and S. n. avicennia) of the 10 subspecies are currently listed with a conservation status of protection. Efforts to conserve and manage fox squirrels in the southeastern United States are constrained by difficulties in studying their populations because of low densities and low detectability. There is a need for an effective survey method to fill knowledge gaps on southeastern fox squirrel ecology. To address this need and to identify a cost-effective and reliable technique to survey and monitor southeastern fox squirrel populations, we compared four survey methods across seasons: live-trapping; camera-trapping; point counts; and line-transect surveys, in regard to whether a detection occurred at a survey point, the total number of detections at a survey point, and the total cost for each method. We assessed the effectiveness of capture and detection methods and...

Reevaluating fox squirrel (Sciurus niger) population declines in the southeastern United States

We used southeastern fox squirrels (Sciurus niger) in the southeastern United States as an example of how modern approaches to estimate density coupled with a reevaluation of previous estimates can provide important new insights into the management and conservation of mammals. There are few rigorous density estimates of southeastern fox squirrels, which hinders our ability to manage and conserve their populations. Based on an initial estimate from 1957 of 38 squirrels/km2 and subsequent decreases in estimates of population densities, noted decreases in hunter harvest reports, and anecdotal observations, southeastern fox squirrels are believed to be declining. To assess the extent of this decline, we first estimated the density of a subspecies of southeastern fox squirrel, Shermans fox squirrel (S. n. shermani), using live trapping and camera trapping and modern analytical approaches for mark–recapture analysis. Then, to compare our densities to previous work, we calculated a standardized effective survey area correction factor for past studies and recalculated their population densities. Once standardized, we found little temporal or geographic variation in densities of southeastern fox squirrels (2.4–8.5 squirrels/km2) spanning nearly 70 years of research. Past densities were substantially lower than initially reported with corrected survey areas, suggesting that densities may have always been naturally low but were incorrectly inflated due to study designs and statistical approaches. Moreover, corrected densities from all studies were correlated with the bounded survey area, suggesting that researches aiming to estimate population densities of southeastern fox squirrels were frequently conducted at scales too small relative to the size of their home ranges. The use of methodological and analytical approaches such as those used in this study may help to avoid misdirected conservation designations or management actions and misuse of conservation funding.

Genetic evidence indicates ecological divergence rather than geographic barriers structure Florida fox squirrels

For polytypic mammal species, biogeographic barriers including rivers have often been used to delineate taxonomic units under the assumption that barriers have structured their distribution. We tested the importance of major riverine systems as biogeographic barriers in fox squirrels (Sciurus niger) across the state of Florida, where 4 currently recognized subspecies are delineated at major rivers. We also explored whether phylogeographic structure may be limited to ecologically divergent subspecies, specifically between S. n. avicennia and S. n. shermani. Using a multilocus approach to examine diversity, we found that restricted gene flow was only present between S. n. avicennia, located south of the Caloosahatchee River in south Florida, and the rest of S. niger, which is widespread across the state. Mitochondrial DNA revealed that 2 divergent groups of haplotypes are present and widespread across Florida, thus supporting the hypothesis that fox squirrels persisted in multiple refugia during the Pleistocene, and that S. n. avicennia diverged ecologically from other populations of fox squirrels relatively recently. This was supported by isolation with migration models that indicated matrilineal isolation since the onset of divergence between S. n. avicennia and S. n. shermani, which corresponds to the onset of ecological divergence in south Florida during the early Holocene. Isolation by distance at 8 microsatellite loci from the western panhandle to the southern end of the peninsula was significant only when S. n. avicennia was included; however, this was due to the hierarchical genetic patterns identified between S. n. avicennia and the other subspecies as determined by Bayesian clustering, and not due to spatially restricted dispersal. We postulate that the demographic isolation of S. n. avicennia is the result of adaptation to the unique ecological conditions of south Florida.

Reintroduction of captive-born beach mice: the importance of demographic and genetic monitoring

Reintroducing native wildlife populations is a common conservation-management approach aimed at reducing the threat of extinction and restoring ecosystem function. Captive-born individuals are sometimes used in reintroductions, but the effectiveness of this strategy is poorly understood due to insufficient post-reintroduction monitoring and evaluation. Our objective was to evaluate the utility of using captive-born individuals of an endangered rodent, the Perdido Key beach mouse (Peromyscus polionotus trissyllepsis) to reestablish a population on the western end of Perdido Key at Gulf State Park, Alabama, from which it was extirpated in 1997. We released 48 captive-born mice in March 2010 and monitored the population through livetrapping across 8 sessions spanning 5 years. We evaluated temporal changes in microsatellite genetic diversity to determine whether mice born in the wild were derived from released mice. The number of mice declined by 73% to 13 individuals in the first 2 weeks after release but increased to an estimated 206 (95% confidence interval = 195–217) individuals after 5 years. Genetic monitoring demonstrated a slight decrease in diversity during the first 3 months but an increase by year 5. Admixture from a neighboring population was detected in year 2 and year 5, which corresponded to the largest increase in population size between trapping sessions. This change in abundance corresponded with a doubling of Ne/N signifying a possible role of admixture in population growth and resilience. This study demonstrates the feasibility of using captive-born beach mice to reestablish populations when wild populations are too small to serve as donors for a translocation. We could not, however, discern how gene flow from an expanding neighboring population affected growth or persistence of the reintroduced population. Our study emphasizes that in future reintroductions, genetics should be monitored together with demographic patterns, because cryptic gene flow could affect how we interpret reintroduction success.