George W. Tanner

USE OF TEMPORARY WETLANDS BY ANURANS IN A HYDROLOGICALLY MODIFIED LANDSCAPE

We examined larval anuran assemblages at 12 temporary wetlands occurring on the MacArthur Agro-Ecology Research center (MAERC) in southcentral Florida. MAERC is an active cattle ranch, and the wetlands on the site are heavily influenced by an extensive series of ditches that drain the landscape. Ditching has resulted in a change from a historically extensive marsh system to a series of isolated wetlands surrounded by upland habitats. Because a majority of anurans in Florida breed exclusively or facultatively in wetlands whose drying regime excludes fish, we were interested in determining the value of these modified wetlands as breeding sites. We examined the effect of wetland size and hydrology on anuran use, and compared breeding activity across three summers that varied greatly in rainfall pattern. We sampled tadpoles from May 93 to August 93 and from May 94 to September 95. A total of 3678 tadpoles from 11 species was collected. Rana utricularia was the most abundant species and the only species found in every wetland Species richness was related positively to wetland size (r=0.65, p=0.023) but not hydroperiod (r=0.03, p=0.93). Tadpole abundance was not related to wetland size (r=0.35, p=0.29) nor hydroperiod (r=0.40, p=0.22). Annual variation in rainfall resulted in significant changes in species composition. A drought during 1993 resulted in no breeding. A high water table in the spring of 1995 resulted in localized flooding in early summer on part of the ranch. Wetlands in these areas were exposed to spillover of water from ditches containing fishes. Wetlands so impacted showed significant changes in species composition from the previous year (x2=1008, p < 0.0001), whereas wetlands that were not impacted did not differ in composition. The wetlands at MAERC provide dynamic habitats that offer varying breeding opportunities that are highly dependent on meteorological conditions.

Effects of cover and predator size on survival and development of Ranautricularia tadpoles

Abstract Size-limited predation is an important process during the development of many aquatic species, and mortality rates of early larval stages and small individuals can be particularly high. Structurally complex habitats can mediate predator-prey interactions and provide a potentially important mechanism for decreasing predation pressure on larvae. To determine whether structurally complex habitats mediate predation on tadpoles of the southern leopard frog (Ranautricularia), we designed a factorial experiment, crossing two levels of cover with three predator treatments (none, small, or large Trameacarolina naiads). Predator size had a larger effect on tadpole performance (survival, mass and age at metamorphosis) than did cover level, largely because small predators were ineffective. Within the large-predator treatment, however, tadpole survival was higher (78%) under high than under low cover (46%), suggesting that increased cover decreased predator foraging efficiency allowing more larvae to reach a size refuge. This study demonstrates that habitat structural complexity can play an important role in mediating predator-prey interactions, even when tadpoles start out at a size disadvantage relative to predators. Consideration of habitat structural complexity in future research should provide a more complete understanding of the role of size relationships in predator-prey systems.

Fire in key deer habitat improves brownse, prevents succession, and preserves endemic herbs

Habitat quality reduced by fire suppression may have influenced the recent decline of Key deer (Odocoileus virginianus clavium). A major foraging habitat for Key deer, the rockland pine community, as well as several plants endemic to this habitat, depend on periodic fires for continued existence. Refuge burning is opposed by residents of nearby urban development. To quantify effects of fire, we measured use and nutritive content of browse for the year following fire, monitored growth of the vegetation after fire, and documented succession in relation to time since the last fire. Browsing by deer was most intense early in the growing season. Deer chose species high in crude protein (CP), phosphorus (P), and in vitro digestibility (IVOMD)

Ungulate relative abundance in hunted and non-hunted sites in Calakmul Forest (Southern Mexico)

The relative abundance of an ungulate community in hunted and non-hunted areas was studied in Calakmul, a tropical forest in southern Mexico that includes a 723,815 ha Biosphere Reserve where no hunting is allowed and communal lands where hunting activity does take place. Tapir, white-lipped peccary (WLP), collared peccary, two species of brocket deer and white-tailed deer were the focal species. Relative abundance of ungulates was obtained by counting tracks along transects in three hunted sites and in the southern core area of the Calakmul Biosphere Reserve, a enforced part of the protected area of 350,000 ha where no hunting has been-permitted since 1989. A total of 1708 ungulates tracks were obtained along 206.1 km (n = 90 transects) divided among the four sites. Relative abundance of the species was estimated from the track encounter rate (TER) calculated as the number of tracks per species encountered per km of transect. No significant differences in brocket deer and collared peccary TER was found among hunted and non-hunted areas. TER for WLP was significant higher in the non-hunted area, while TER for white-tailed deer and tapir was significant higher in hunted sites. Hunting activity affected the ungulate species in Calakmul differently. Brocket deer, white-tailed deer and collared peccary are more resistant species toward the hunting pressure than the WLP, who needs an immediate protection plan throughout Calakmul. Hunting areas are important habitat refuges for tapir populations and they should be protected in these areas.ResumenLa abundancia relativa de seis especies de ungulados fue obtenida a través de conteos de huellas a lo largo de transectos en tres sitios con cacería y en la parte sur de la Reserva de la Biosfera de Calakmul, una área de alrededor de 350,000 ha donde la cacería ha sido prohibida desde 1989. Tapir, pecarí de labios blancos, pecarí de collar, dos especies de venados temazates y el venado cola blanca fueron las especies estudiadas. Un total de 1708 huellas de ungulados fueron obtenidos a lo largo de 206.1 km (90 transectos) divididos en los cuatro sitios. La abundancia relativa de las especies fue estimada por medio de la tasa de encuentro de huellas (TEH) calculado como el número de huellas encontradas por km de transecto recorrido. La TEH de los venados temazates y el pecarí de collar fue similar entre las áreas con cacería y sin cacería. La TEH para el pecarí de labios blancos fue significativamente mayor en el área sin cacería, mientras que la TEH del venado cola blanca y el tapir fueron significativamente mayor en los sitios con cacería. La actividad de cacería afecta a las especies de ungulados diferente en la región de Calakmul. Los venados temazates, el venado cola blanca y el pecarí de collar están resistiendo mejor la presión de cacería que el pecarí de labios blancos quien necesita un plan inmediato de protección en toda el área. La evidencia sugiere que las áreas con cacería en este estudio son importantes para las poblaciones de tapir, y que se debe prestar atención a su protección en dichas áreas.

Home Range and Habitat Preferences of White-Lipped Peccaries (Tayassu pecari) in Calakmul, Campeche, Mexico

Abstract The white-lipped peccary (Tayassu pecari) is a neotropical ungulate that forms some of the largest groups living in dense tropical forest. Populations of this species have declined throughout Mesoamerica during the last 50 years at alarming rates. Home-range and habitat preferences of this species have been documented in Brazil and Costa Rica for humid tropical forest. Here we studied home-range features and habitat preferences of white-lipped peccaries for a seasonally dry tropical forest of the Yucatan Peninsula—the Calakmul Biosphere Reserve—where water and food can be temporarily scarce or even absent. By using radiotelemetry and direct observations for 18 months of individuals in 4 groups, we documented some of the largest home ranges reported for some of the smallest group sizes documented for this species. Dry-season home ranges were constrained to the close vicinity of a few available water sources, whereas during the rainy season peccary groups were more mobile and traversed long distances. Compositional analyses of habitat preferences indicated that groups preferred ponds and Medium Sub-Perennial Forest in combination with Low Flooded Forest, whereas the least preferred was the Dry Forest. Apparently, the combination of ranging over large areas to access widely dispersed resources while living in smaller groups and sharing space allows white-lipped peccaries to survive in Calakmul.

Species diversity and diversity profiles: concept, measurement, and application to timber and range management.

The concepts and use of several diversity assessments are presented and applied to a practical situation. Burning, mechanical methods of site preparation, and cattle grazing are common disturbances in forests of the South. Their influence on plant diversity indices are examined in a longleaf-slash pine forest of north Florida. Species richness, Shannons index, and Simpsons index showed increases in diversity shortly following burning and site preparation and a trend toward pre-treatment conditions after 6 years. Deferred-rotation grazing systems had no influence. Comparative diversity profiles showed similar trends but were more informative by providing both qualitative and quantitative information. These techniques are useful for assessing community responses to management practices, that is, they are effective methods for understanding the impacts of forest management and range management practices on plant community structure and succession.

Effects of Cover and Predator Identity on Predation of Hyla squirella Tadpoles

Habitat structural complexity can strongly affect biotic interactions. In particular, the intensity of predator-prey interactions can be mediated by habitat complexity because the effectiveness of predators often decreases in structurally complex habitats (Werner et al., 1983; Diehl, 1988; Babbitt and Jordan, 1996). Typically, increased habitat complexity reduces predation rates by providing refuges for prey or by decreasing predator efficiency (Crowder and Cooper, 1982; Savino and Stein, 1982; Werner et al., 1983). The role of habitat structure in mediating predatortadpole interactions is potentially important because predation is a significant source of mortality of anuran tadpoles (Calef, 1973; Heyer et al., 1975; Smith, 1983). Species breeding in permanent ponds display a wide array of anti-predator defenses for avoiding predation by fish (Formanowicz and Brodie, 1982; Kats et al., 1988; Lawler, 1989). In general, such defenses are lacking in species that breed in ephemeral ponds (Kats et al., 1988). In addition, activity rates of tadpoles in temporary ponds often are higher compared to species in permanent ponds (Woodward, 1983). Because many predators of tadpoles are gape-limited, rapid growth to a size refuge is an important mechanism for escaping predation (Crump, 1984; Travis et al., 1985; Richards and Bull, 1990; but see Crump and Vaira, 1991). For species breeding in ephemeral environments, rapid growth is also important for decreasing risk of desiccation (Wilbur, 1987; Newman, 1989). However, trade-offs exist between rapid growth and predator avoidance because actively foraging tadpoles are more likely to be detected by predators (Woodward, 1983; Werner and Anholt, 1993; Skelly, 1994). Although ephemeral ponds lack fish predators, these sites often contain aquatic insect predators that also are significant mortality agents (Smith, 1983; Wilbur and Fauth, 1990). Therefore, any mechanism that can reduce predator efficiency without decreasing foraging activity could enhance tadpole survival, particularly in ephemeral environments. Because structurally complex habitats can reduce predator foraging efficiency, complex environments may provide tadpoles with partial protection from predators, even when tadpoles are actively foraging. In this study we examine how habitat structure affects predation rates on squirrel treefrog (Hyla squirella) tadpoles. Hyla squirella is a common anuran in Florida, and is often numerically dominant in the ephemeral sites in which it breeds (Babbitt, unpubl. data). Hyla squirella tadpoles are active foragers even

Graminoid community composition and structure within four everglades management areas

Estimates of species density, percentage vegetative cover, biomass, and sawgrass (Cladium jamaicense) height were made in Tall Sawgrass, Medium Sawgrass, and Wet Prairie communities in the SE portion of Water Conservation Area 3A (3A), the SW portion of Water Conservation Area 3B (3B), the NW portion of Northeast Shark Slough (NSS), and the NE portion of Everglades National Park (ENP) during dry season and wet season sampling periods in 1986 and 1987. We summarized the history of water management and hydroperiod manipulation in the study area. Wet Prairie had the deepest water of the three plant communities studied, while 3A had deepest water and longest hydroperiod of the four areas. Generally, the greatest species density occurred in NSS, where water was shallowest. Individual sawgrass plants and their basal tussocks were taller in 3A than in the other three areas, which may make plants in 3A more susceptible to damage by airboats and fire. Cover and biomass of sawgrass fluctuated more between sampling periods than among management areas, which rendered lower measurements in Tall Sawgrass in 3B non-significant. Species composition of Wet Prairies, particularly in 3A whereRhynchospora spp. were absent, andNymphaea odorata was dominant, resembled aquatic sloughs. The low species density in the study area may be related to rapid fluctuations in water levels that could drown slow-growing plants, and to infrequent dry periods that preclude seed germination. Species richness was low, compared with other Everglades plant community studies. No annual emergent plants were encountered.

Avian community response to fire and mechanical shrub control in south Florida.

Effects of prescribed fire and roller chopping applied in 2 seasons on woody vegetation and the associated avian community of a southwestern Florida former dry prairie were studied. There were 5 vegetation treatments with 2 replications of each; treatments were control, winter burn, winter chop, summer burn, and summer chop. Percent shrub cover was sampled with line intercept transects. Birds were censused 25 times using the variable circular plot method. Burning in either season reduced shrub cover temporarily; chopping in either season reduced shrub cover significantly and it remained reduced throughout the 15 months of this study. Bird species richness and abundance were similar in control and burn plots. Birds were not seen in summer chop plots up to 5 months posttreatment. Bird species richness and abundance remained low in both winter and summer chop plots. Bird species that were observed in chop plots were mostly open country, grassland inhabitants, indicating a trend toward prairie restoration.

SPATIAL AND TEMPORAL ECOLOGY OF EASTERN SPADEFOOT TOADS ON A FLORIDA LANDSCAPE

Effective amphibian conservation must consider population and landscape processes, but information at multiple scales is rare. We explore spatial and temporal patterns of breeding and recruitment by eastern spadefoot toads (Scaphiopus holbrookii), using nine years of data from continuous monitoring with drift fences and pitfall traps at eight ephemeral ponds in longleaf pine-wiregrass sandhills. Breeding events (≥25 adults at a pond within a month) occurred 23 times on nine occasions at seven of the eight study ponds, but substantial recruitment (≥100 metamorphs) followed only five events. Recruitment ranged from 0–4648 among ponds. Only four ponds functioned as population “sources”, and only during some years. The other ponds, and even “source” ponds during some years, functioned either as “sinks,” where breeding occurred with no resulting recruitment, or were not used at all for breeding. Most recruitment occurred during four years. Recruitment was correlated with adult breeding effort, but only during some years. Recaptures were rare, and inter-pond exchange of adults was minimal and short-distance (<130 m; one was 416 m). Most (83.5%) individuals captured were metamorphs, and 15.9% were ≥51 mm (est. ≥4 yr). We conservatively estimated a 7-yr lifespan. Adult “population” trends clearly reflected breeding effort rather than numbers per se; capture rates fluctuated dramatically among years, but showed no overall trends during the 9-yr study. Our paper is provides empirical information that can be used to generate realistic metapopulation models for S. holbrookii as a tool in conservation planning.