I. Jack Stout

Effects of repeated burning on species richness in a Florida pine savanna: A test of the intermediate disturbance hypothesis

Abstract. We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaikes Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model.

Population genetics and conservation of the threatened southeastern beach mouse (Peromyscus polionotus niveiventris): subspecies and evolutionary units

We investigated genetic diversity within the southeastern beach mouse (SEBM-Peromyscus polionotus niveiventris) and also tested the hypothesis that the subspecies recognition of P.p. niveiventris, based on size and color differences, is congruent with this taxon representing a discrete evolutionary lineage. We used ten polymorphic microsatellite loci and mitochondrial cytochrome-b gene DNA sequences to investigate genetic diversity and population structure within the SEBM, and to determine the level of divergence between the SEBM and the nearest known inland subspecies of the oldfield mouse (Peromyscus polionotus rhoadsi). Moderate genetic distances were observed between the SEBM and the inland oldfield mouse based on microsatellite data, with FST values ranging from 0.11 to 0.22 between these taxa. Additionally, mitochondrial DNA haplotypes of the SEBM formed a distinct monophyletic group relative to haplotypes sampled from P. p. rhoadsi. Based on previous estimates of rates of mitochondrial DNA evolution in rodents, we inferred that Pleistocene sea-level fluctuations are likely responsible for the historical isolation of the SEBM lineage from mainland P. polionotus. Our data demonstrate the genetic distinctiveness of the SEBM, justifying the current subspecies designation for the SEBM and its continued protection under the United States Endangered Species Act. We classify the Cape Canaveral and Smyrna Dunes Park populations of SEBM as a single evolutionary significant unit. The two known extant allopatric populations of the SEBM showed some differentiation in microsatellite frequencies and were moderately reciprocally distinguishable based on assignment to distinct genetic clusters by a Bayesian admixture procedure. These results justify the classification of these two extant SEBM populations as distinct management units that should be independent targets of management and conservation attention.

Dispersion and habitat occupancy of the beach mouse, Peromyscus polionotus niveiventris

Dispersion and intragrid movements of Peromyscus polionotus were studied in coastal dune vegetation on Merritt Island, Florida, USA. Three contiguous zones of vegetation ran parallel with the beach and dune lines. Zone 1 was seaward and supported sea oats, Uniola paniculata. Zone 2 was characterized by clumps of palmetto, Serenoa repens , and sea grape, Coccoloba uvifera , and expanses of open sand. Zone 3 was interior and consisted of dense scrub dominated by palmetto, sea grape, and wax myrtle, Myrica cerifera. The ranking of the zones in terms of observed first captures was zone 1 > 3 ≥ 2, whereas for recaptures it was zone 2 > 3 > 1. A reasonable explanation for the discrepancy between the distributions of first captures and recaptures among zones was a net movement of individuals from zone 1 to zones 2 and 3. The distribution of first-captures among the zones was not significantly different during the stable, exponential, and peak phases of population growth; however, significantly ( P < 0.05) more first captures were from zone 1 during the decline phase. Average recapture density was greater in zones 2 and 3 than in zone 1 during all phases of population change. Most of the movement of animals from zone 1 to zones 2 and 3 occurred during the periods of stable low densities and exponential population growth. The overall pattern of habitat occupancy seems to have been one in which the preferred habitat (zones 2 and 3) filled first, with the marginal area (zone 1) filling more slowly and even contributing individuals to the preferred sites. At peak and declining densities, the preferred habitat no longer received individuals from the marginal area.

Qualitative and Quantitative Studies on Chironomidae (Diptera) and Selected Physico-Chemical Parameters in Two Tributaries of the Wekiva River, Central Florida

Aquatic midge (Chironomidae: Diptera) larval densities, 24-h adult emergence, and larval and adult dry biomass were estimated monthly for two years in two tributaries of the Wekiva River, central Florida, along with selected physico-chemical water parameters. Twenty-four genera of midges were identified in Blackwater Creek and 26 in Rock Springs Run, with subfamily Chironominae dominating the midge fauna. Larval densities in the former stream ranged from 56 to 757 per m 2, with 24-h periods adult emergence ranging from 0 to 95 per m 2 . The latter stream supported 138 to 1277 larvae per m 2 with 0 to 68 emergent adults per m 2 taken during 24-h periods. Mean larval biomass in Rock Springs Run (42 mg per m 2 ) was significantly (P<0.05) higher than in Blackwater Creek (27 mg per m 2 ), while mean adult biomass in both habitats was essentially identical (1.1 mg per m 2 ). Annual midge productivity estimates (1.12 g dry wt per m 2 ) in each stream indicated that both were oligotrophic. Water volume was the overriding abiotic factor noted in both habitats, influencing many of the observed water parameters and altering the midge generic composition, especially in Blackwater Creek.

Life History and Productivity of Hexagenia limbata (Ephemeroptera: Ephemeridae) and Selected Physico-Chemical Parameters in Two Tributaries of the Wekiva River, Central Florida

Nymphal densities and size frequency distribution of Hexagenia limbata (Serville), a burrowing mayfly, were determined monthly for two years in two tributaries of the Wekiva River, central Florida, along with selected physico-chemical water parameters. Blackwater Creek supported a mean number of 112 (range 0-434) and Rock Springs Run 89 nymphs per m 2 (range 11-258). The mayfly species displayed a univoltine life history with adult emergence peaking in August. Productivity in Blackwater Creek was estimated at 4.688 g per m 2 and in Rock Springs Run at 3.123 g per m 2 . Productivity/biomass ratios were estimated at 4.09 and 4.59 in Blackwater Creek and Rock Springs Run, respectively. The nymphal densities in both streams were positively correlated with water pH and negatively correlated with water volume. Apparently, water volume was the overriding abiotic factor in both streams, influencing several measured water parameters and as well as nymphal populations during the study period.

Unraveling natural versus anthropogenic effects on genetic diversity within the southeastern beach mouse (Peromyscus polionotus niveiventris)

Anthropogenic habitat loss is among the greatest threats to biodiversity. Populations undergoing fragmentation and loss of habitat are also threatened by erosion of genetic diversity. However, contemporary genetic diversity may be the legacy of natural processes acting prior to anthropogenic influences. Measurements of genetic diversity from contemporary and historical samples can evaluate the relative impact of natural and anthropogenic effects on its status. We investigated the genetic diversity of a threatened subspecies occupying Atlantic Coast barrier islands of Florida, Peromyscus polionotus niveiventris (southeastern beach mouse). To test for recent loss of genetic diversity, we compared cyt b data from museum samples (historical—prior to human impact) with contemporary samples throughout their range. Ten microsatellite loci were genotyped for samples from the contemporary range, to determine current population interconnectedness and structure. The results using cyt b data revealed no statistically significant loss of genetic diversity between historical and contemporary populations of P. p. niveiventris. Both nuclear and mitochondrial data support our conclusion that the observed capture and conservation of historical genetic diversity is explained by the large federally protected region of continuous habitat that remains with minimal human impact. Whereas, the two disjunct populations isolated by anthropogenic habitat destruction, exhibit significant losses of genetic diversity. Collectively, these findings offer a sound basis from which to formulate a conservation strategy to maintain the genetic diversity of P. p. niveiventris. Furthermore, our study underscores the importance of large expanses of continuous habitat within the geographic range of species to facilitate the maintenance of genetic integrity.

Sample Grain Influences the Functional Relationship Between Canopy Cover and Gopher Tortoise (Gopherus polyphemus) Burrow Abandonment

Abstract Change in vegetation structure alters habitat suitability for the threatened gopher tortoise (Gopherus polyphemus). An understanding of this dynamic is crucial to inform habitat and tortoise management strategies. However, it is not known how the choice of the sample grain (i.e., cell size) at which vegetation structure is measured impacts estimates of tortoise–habitat relationships. We used lidar remote sensing to estimate canopy cover around 1573 gopher tortoise burrows at incrementally larger sample grains (1–707 m2) in 450 ha of longleaf pine (Pinus palustris) savanna. Using an information theoretic approach, we demonstrate that the choice of grain size profoundly influences modeled relationships between canopy cover and burrow abandonment. At the most supported grain size (314 m2), the probability of burrow abandonment increased by 1.7% with each percent increase in canopy cover. Ultimately, detecting the appropriate sample grain can lead to more effective development of functional relationships and improve predictive models to manage gopher tortoise habitats.

Cotton Rat Invasion of Sand Pine Scrub Habitat

Cotton rats ( Sigmodon hispidus ) invaded sand pine scrub in central Florida in 1974. One episode of dispersal was observed in January–March and a second commenced in May and ceased in November. Invasion was not observed on three study grids during 1973, 1975, or 1976. Small numbers of immigrant cotton rats settled on the grids during 1974 and breeding took place; however, 60% of the individuals tagged and released were not recaptured. These latter animals were presumed to have continued to disperse. Supplemental food on one of the study grids did not prevent the decline of cotton rats in 1974. The sand pine scrub appeared to have acted as a dispersal sink for cotton rats which underwent dispersal from more optimal habitat in surrounding pine flatwoods. Dispersing animals were healthy, equally divided between the sexes, and included all weight classes.

Colonization and divergence: phylogeography and population genetics of the Atlantic coast beach mice

Barrier island taxa provide an opportunity to investigate recent evolutionary processes, such as colonization and isolation of recently diverged taxa, and provide important insights into understanding contemporary diversity and the assessment of conservation units. Using rapidly evolving genetic markers (mitochondrial DNA and microsatellites), we studied the Atlantic coast beach mouse subspecies (Peromyscus polionotus decoloratus, P. p. niveiventris, and P. p. phasma). Our data indicate that each of the extant coastal subspecies (P. p. niveiventris and P. p. phasma) is comprised of unique haplotypes indicative of their isolation, while the extinct subspecies, P. p. decoloratus, contain a single haplotype, which was shared with P. p. phasma. Moreover, all the coastal haplotypes originate from a single mainland haplotype found in central Florida, USA. The microsatellite data indicated high levels of genetic structure among our sampled populations. Additionally, these data group the populations into three distinct genetic clusters, with each of the extant coastal subspecies belonging to their own cluster and the mainland individuals forming a separate cluster. The extant Atlantic coast beach mice are on separate evolutionary trajectories, thus representative of separate taxonomic units. Therefore, the data support that two extant subspecies on the Florida Atlantic coast fit the Distinct Population Segment designation and should be managed and conserved as two separate independent units.