Kenneth M. Portier

Density-dependent habitat selection and performance by a large mobile reef fish.

Many exploited reef fish are vulnerable to overfishing because they concentrate over hard-bottom patchy habitats. How mobile reef fish use patchy habitat, and the potential consequences on demographic parameters, must be known for spatially explicit population dynamics modeling, for discriminating essential fish habitat (EFH), and for effectively planning conservation measures (e.g., marine protected areas, stock enhancement, and artificial reefs). Gag, Mycteroperca microlepis, is an ecologically and economically important warm-temperate grouper in the southeastern United States, with behavioral and life history traits conducive to large-scale field experiments. The Suwannee Regional Reef System (SRRS) was built of standard habitat units (SHUs) in 1991-1993 to manipulate and control habitat patchiness and intrinsic habitat quality, and thereby test predictions from habitat selection theory. Colonization of the SRRS by gag over the first six years showed significant interactions of SHU size, spacing, and reef age; with trajectories modeled using a quadratic function for closely spaced SHUs (25 m) and a linear model for widely spaced SHUs (225 m), with larger SHUs (16 standardized cubes) accumulating significantly more gag faster than smaller 4-cube SHUs (mean = 72.5 gag/16-cube SHU at 225-m spacing by year 6, compared to 24.2 gag/4-cube SHU for same spacing and reef age). Residency times (mean = 9.8 mo), indicative of choice and measured by ultrasonic telemetry (1995-1998), showed significant interaction of SHU size and spacing consistent with colonization trajectories. Average relative weight (W(r)) and incremental growth were greater on smaller than larger SHUs (mean W(r) = 104.2 vs. 97.7; incremental growth differed by 15%), contrary to patterns of abundance and residency. Experimental manipulation of shelter on a subset of SRRS sites (2000-2001) confirmed our hypothesis that shelter limits local densities of gag, which, in turn, regulates their growth and condition. Density-dependent habitat selection for shelter and individual growth dynamics were therefore interdependent ecological processes that help to explain how patchy reef habitat sustains gag production. Moreover, gag selected shelter at the expense of maximizing their growth. Thus, mobile reef fishes could experience density-dependent effects on growth, survival, and/or reproduction (i.e., demographic parameters) despite reduced stock sizes as a consequence of fishing.

Soil Phosphorus, Cattle Stocking Rates, and Water Quality in Subtropical Pastures in Florida, USA

Abstract Minimizing nonpoint source nutrient pollution is important to the sustainability of grazing lands. Increased nutrient loads have reduced water quality in Lake Okeechobee in south Florida, prompting establishment of a Total Maximum Daily Load (TMDL) that will require large reductions in phosphorus (P) runoff into the lake. A significant portion of this reduction must come from beef cattle ranches, the major land use in the region. A large-scale research project, consisting of a 420-ha array of 8 improved summer and 8 semi-improved winter pastures, was established from 1998–2003 to investigate the influence of beef cattle stocking rate on nutrient loads in surface runoff. Each pasture type had two replicates of four different cattle stocking rates including a control with no cattle and stocked pastures with low, medium, and high stocking rates (1.3, 1.0, 0.6 ha·AU−1 [animal unit] in summer pastures; 2.1, 1.6, and 0.9 ha·AU−1 in winter pastures). Cattle stocking rate did not affect nutrient concentrations or loads in surface runoff during the study period. Average annual P discharges were 1.71 kg·ha−1 from summer pastures and 0.25 kg·ha−1 from winter pastures. Average total P concentrations in runoff were 0.63 mg·L−1 for summer pastures and 0.15 mg·L−1 for winter pastures. Differences in runoff P were related to differences in soil P test results, a difference believed to be due to prior fertilization practices. Our findings show that reducing cattle stocking rates on beef cattle pastures is not an effective practice for reducing nutrient loads, and that accumulation of P in soil from historical fertilization has an overriding influence on P loads in surface runoff. Results indicate that reducing the overall volume of surface discharges would be a more effective strategy than altering cattle stocking practices to reduce nonpoint runoff of P from cattle pastures in this region.

Dicotyledonous wood anatomical characters as predictors of climate

Abstract The relationships among wood anatomical characters and climate are examined for 50 wood anatomical features in floras from 37 regions in North America, South America, Africa and Malaysia. Correlations, simple regressions and multiple regressions, were used to develop models for the prediction of climate from wood anatomy. The climate variables considered were: mean annual temperature, mean annual range in temperature, cold month mean temperature, mean annual precipitation, precipitation of the driest month and length of the dry season. Good correlations were found with temperature; poorer correlations with precipitation. The climate variables, especially the temperature-related ones, were best predicted by two or more wood anatomical characters considered together. Characters that we selected to calculate climate variables are: vessels with multiple perforations; spiral thickenings present in the vessels; vessel mean tangential diameter less than 100 μm; fibers septate; rays commonly more than 10 cells wide; rays heterocellular with four or more rows of upright cells; rays storied; axial parenchyma absent or rare; marginal parenchyma present; and wood ring-porous. Models were validated on seven temperate and six tropical sites. Based on these results, a method for determining paleoclimate from fossil wood assemblages is suggested.

Evaluation of Prerelease, Postrelease, and Total Mortality, of Largemouth Bass Caught during Tournaments, in Two Florida Lakes

Abstract Eleven fishing tournaments for largemouth bass Micropterus salmoides floridanus, held on two Florida lakes during July 1984-June 1985, were studied to quantify fish mortality and to evaluate associations between mortality and environmental and tournament conditions. Post-release mortality was determined by holding largemouth bass in floating mesh cages for 14 or 21 d. Prerelease, postrelease, and total mortality averaged 18.6% (range, 0.8-42.8%), 10.0% (2.2-26.7%), and 26.7% (5.2-47.8%), respectively. Prerelease and total mortality were significantly (P ≲ 0.05) related to water temperature but not significantly related to air temperature, cumulative radiation, number of teams, mean catch per team, or mean weight per fish. Postrelease mortality was not significantly related to any measured variable. Most postrelease mortality occurred during the first 6 d after the tournament, and the greatest single-day postrelease mortality occurred within 24 h. We observed no gross pathology among the fish held...

Patterns of change in tree islands in Arthur R. Marshall Loxahatchee National Wildlife Refuge from 1950 to 1991.

Size, shape, orientation, and distribution of tree islands in a remnant of northern Everglades wetland were examined from 1950 and 1991 aerial photography. The objectives were to quantify the patterns of tree islands in Loxahatchee National Wildlife Refuge, to determine if the patterns of tree islands had changed between the two dates, and to relate the tree island patterns to modeled pre-and post-drainage hydrologic patterns. There was considerable variation in the patterns of tree islands spatially and temporally Changes in the size and shape of tree islands from 1950 to 1991 are consistent with changes in the modeled pre-and post-drainage hydrologic patterns. Photo plots along the edges of the refuge, where hydroperiods are longer and depths deeper than they were historically, show a decrease in tree island size and in overall area of tree islands in the plots. Photo plots in the interior, where hydroperiods are shorter than they were pre-drainage, show an increase in tree island area. Overall, there is a tendency for more tree islands to be irregularly shaped in the 1991 photo plots than in the 1950 plots, a reflection of the loss of water flow, reduction of pulse magnitude, and the ponding of water along the perimeter dikes. This study illustrates the importance of considering long-term changes in hydroperiod, depths, and water flows in the restoration of this area.

Life history analysis for black bears (Ursus americanus) in a changing demographic landscape

We used matrix population models to evaluate the relative importance of different vital rates to population growth (λ) for female black bears on the Southeastern Coastal Plain (SCP) of the United States, and to determine whether reductions in subadult and adult survival due to ongoing habitat fragmentation and human disturbance will cause shifts in the relative importance of vital rates. Additionally, we evaluated how well predictions made by Heppell et al. [Ecology 81 (2000) 654] concerning elasticity patterns for mammals apply to black bears over realistic variation in vital rates, and how much correlations between vital rates will influence their relative effects on λ. We generated 500 model replicates based upon different combinations of vital rate values for each of nine scenarios, where scenarios represented different combinations of reduction in survival and level of correlation among vital rates. Elasticity analysis indicated that adult survival, and litter size of three- and four-year-old females are most important to λ in 99.3 and 0.7% of all replicates, respectively; the few replicates with higher elasticity for litter size occurred in scenarios with some type of correlation among vital rates; of these, 21 (70.0%) occurred in scenarios with 20% reductions in subadult and adult survival. Results from elasticity analysis, indicating the strong and consistent effect of adult survival, are also supported by results from regression analysis. In all scenarios, the regressions of λ on the vital rates showed that adult survival accounted for the majority of variation in λ. Our results suggest that adult survival should be the primary target of conservation and management strategies. Ongoing human impacts on subadult and adult survival reduce the frequency of conditions in which populations on the SCP are stable or increasing. Without conservation strategies that reverse this trend, local extinctions will become more likely, and recovery of at-risk populations will be more difficult to achieve.

Modeling Florida panther movements in response to human attributes of the landscape and ecological settings

This paper describes the development and results of an individual-based spatially explicit model created to assist in the potential reintroduction of the Florida panther (Puma concolor coryi) to northern Florida, an area within its former range. The PANTHER model was created to incorporate human attributes of the landscape with ecological attributes to evaluate and identify landscape features and conservation strategies that will be critical to a population of panthers. The model mimics panther movement behavior using a C++ program, and implements panther moves over Geographic Information Systems (GIS) maps depicting land cover, roads, deer densities, and human densities. Sensitivity analysis revealed home range sizes were most sensitive to how panthers perceived the landscape, their place of reintroduction on the landscape, and gender-based rules. Panther interactions were dependent on perception distances. Home range placement within the study area was most similar to field studies when panthers ranked cypress as a tertiary rather than a secondary preferred land cover type. Model simulation results indicated locations along the Suwannee River where Florida panthers and humans would prefer to reside, both under 1990s landscape conditions, and under two possible future scenarios that predicted future human development. As human density and development were increased the use of hardwood hammocks (a land cover preferred by panthers) was predicted to decrease. Simulation results also indicated that panthers increased use of several other land cover types, were subjected to increased mortality on roads, and constricted their home ranges as human density and development increased. Model results can be used to support conservation actions that restrict development in areas along rivers and identify landowners who own land panthers would most likely use.

Effects of local extinction of the plains vizcacha (Lagostomus maximus) on vegetation patterns in semi-arid scrub

We studied spatial and temporal effects of local extinction of the plains vizcacha (Lagostomus maximus) on plant communities following widespread, natural extinctions of vizcachas in semi-arid scrub of Argentina. Spatial patterns in vegetation were examined along transects extending outward from active and extinct vizcacha burrow systems. Responses of vegetation to removal of vizcachas were assessed experimentally with exclosures and by documenting vegetation dynamics for 6 years following extinctions. Transect data demonstrated clear spatial patterns in plant cover, particularly an increase in perennial grasses, outward from active vizcacha burrows. These patterns were consistent with predictions based on foraging theory and studies that document grasses as the preferred food of vizcachas. Removal of vizcachas, experimentally and with extinctions, resulted in an immediate increase in perennial and annual forbs indicating that intense herbivory can depress forb cover, as well as grasses. After a 1-year lag following cessation of herbivory, cover of grasses increased. Forbs declined as grasses increased. The long-term effect of extinction of vizcachas was a conversion of colony sites from open patches dominated by forbs to dense bunch grass characteristic of the matrix. Major changes in vegetation occurred within 2–3 years after extinction, resulting in a large pulse of landscape change. However, some species of grasses were uncommon until 5–6 years after the vizcacha extinction. With extinction and colonization, vizcachas generate a dynamic mosaic of patches on the landscape and create temporal, as well as spatial, heterogeneity in semi-arid scrub.

Statistical Issues in Assessing Anthropogenic Background for Arsenic

Conceptual and statistical issues surrounding the estimation of a background concentration distribution for arsenic are reviewed. How background area is defined and samples collected are shown to impact the shape and location of the probability density function that in turn affects the estimation and precision of associated distributional parameters. The overall background concentration distribution is conceptualized as a mixture of a natural background distribution, an anthropogenic background distribution and a distribution designed to accommodate the potential for contamination site samples being included into the background sample set. This concept is extended to a discussion of issues surrounding estimation of natural and anthropogenic background distributions for larger geographic areas. Finally, the mixture model is formally defined and statistical approaches to estimating its parameters discussed.

Protocol Development for Assessing Arsenic Background Concentrations in Florida Urban Soils

Knowledge of arsenic background concentrations in urban soils is important for making remediation decisions. The soil cleanup target level (SCTL) for arsenic in Florida lies within the range of arsenic background concentrations. The residential SCTL is also near the practical quantification limits using analytical procedures. Currently no standard protocols are available for determining arsenic background concentrations in urban soils, apart from site-specific cases. Therefore, a pilot study was conducted to develop and employ appropriate protocols to determine arsenic distribution in urban soils. This involved: site selection (e.g. size and sampling frame), sample collection (e.g. sampling technique), and statistical considerations (e.g. design). Factors such as ease of sample collection and maintaining anonymity of private properties were also considered as they influence the successful implementation of the study. Forty surface soil samples each were collected from five categories in three land use classes (residential-yard and right-of-way, commercial and public land-parks and public building), digested using EPA method 3051a and analysed using graphite furnace atomic absorption spectrometry. Experiences from the pilot study (e.g. complications during sample selection, digestion, data censoring etc.) were used in the development of the final protocol to be used in determining the distribution of arsenic in urban areas.