Cyclic Drought, Dispersal, and the Conservation of the Snail Kite in Florida: Lessons in Critical Habitat

Estudios realizados sobre el Halcón Caracolero de Florida, un ave en peligro de extinción que habita areas pantanosas y se alimenta de caracoles, ilustra los problemas asociados con la protección de hábitats de especies migratorias y nómadas que requieren de habitats disyuntos. Anteriomente a una sequía en el año 1985, la muyoría de halcones caracoleros se observaban en las areas extensas de la región pantanosa de los Everglades a donde nidificaban Sin embargo, durante la sequía el 60% de los halcones observados se localizaron en areas pantanosas más pequeñas ubicadas, en su mayoria eta la región de Palm Beach y et condados vecinos A pesar de que estas pequeñas areas sirven como importantes refugios de emergencia para los hálcones durante epocas de sequia, estas no estan designadas como "hábitat critico" y estan siendo rápidamente transformadas por las presiones de desarrollo. Se discuten problemas de incertidumbre, de efectosa cumulativos, y de transigencia en la evaluación de propuestas para el desarrollo y en la protección de pequeños hábitats aislados Hemos identificado areas de refugio, usadas por los hálcones durante la epoca de sequia y sugerimos maneras para conservar esta especie en Florida mitigando las grandes disminuciones de la población causadas por las sequias. Tambien se evalua la utilidad de una red de comunicación para el reporte de observaciones que sirva para la evaluación de datos de dispersión     

Strategic Habitats for Biodiversity Conservation in Florida

Abstract: Privately owned lands support a large portion of the biodiversity in some areas, but procedures for identifying those private lands critical to the maintenance of biodiversity vary tremendously. We used habitat-based distribution maps in combination with population conservation goals to help identify strategic habitats on private lands in Florida. We used a vegetation map, occurrence data, and published life-history information to create habitat-based distribution maps for 179 rare taxa. We estimated the security of 130 of the taxa by overlaying public land boundaries on habitat maps and then estimating whether conservation lands satisfied a population goal of supporting at least 10 populations of approximately 200 breeding adults. The remaining taxa were evaluated in terms of number of occurrence records on conservation lands. Of the 179 taxa evaluated, existing conservation lands did not adequately protect 56. We then identified habitats on private lands that could best satisfy the minimum conservation goal or else significantly enhance the survival potential of inadequately protected taxa. Strategic habitats included a mix of large and small sites, incorporated some corridor or stepping-stone connections among habitat patches, and protected multiple species. Additional strategic habitats were identified for shorebirds, four natural plant communities, and 105 globally rare plants. The strategic habitats identified in Florida cover 1.65 million ha (12% of the land area) and would cost $8.2 billion (about 15% of Florida's annual state budget) to purchase and $122 million per year to manage. Existing conservation lands account for 3.07 million ha (22% of the land area).     

Targeting Ecosystem Features for Conservation: Standing Crops in the Florida Everglades

Abstract: The Everglades in southern Florida, U.S.A., is a major focus of conservation activities. The freshwater wetlands of the Everglades do not have high species richness, and no species of threatened aquatic animals or plants live there. We have, however, identified a distinctive ecological feature of the Everglades that is threatened by canal construction, draining, and nutrient enrichment from agricultural runoff. Compared to values reported from other freshwater systems, standing stocks of periphyton in relatively undisturbed areas of the Everglades were unusually high, and standing stocks of invertebrates and fish were unusually low. Averaging data gathered from nine sites and five sampling periods spanning 1 year, we found that periphyton standing crop was 88.2 g/m² (ash-free dry mass), invertebrate standing stock was 0.64 g/m² (dry mass), and fish standing stock was 1.2 g/m² (dry mass of large and small species combined). We found that fish standing stocks were much higher in phosphorus-enriched sites than in nearby reference sites but that invertebrate standing stocks were similar in enriched and reference sites. Our results support the notion that oligotrophy is at least partially responsible for the low standing stocks of fish, but they also suggest that species interactions and a paucity of deep-water refugia are important. Anthropogenic eutrophication in Everglades marshes will lead to the loss of distinctive ecosystem features. A focus on species richness and "hot spots" of threatened species provides no basis for conservation of ecosystems like the Everglades. If oligotrophic ecosystems often have low species richness, they will be underrepresented in preservation networks based on some common criteria for establishing conservation priorities.     

The Potential for Species Conservation in Tropical Secondary Forests

Abstract: In the wake of widespread loss of old‐growth forests throughout the tropics, secondary forests will likely play a growing role in the conservation of forest biodiversity. We considered a complex hierarchy of factors that interact in space and time to determine the conservation potential of tropical secondary forests. Beyond the characteristics of local forest patches, spatial and temporal landscape dynamics influence the establishment, species composition, and persistence of secondary forests. Prospects for conservation of old‐growth species in secondary forests are maximized in regions where the ratio of secondary to old‐growth forest area is relatively low, older secondary forests have persisted, anthropogenic disturbance after abandonment is relatively low, seed‐dispersing fauna are present, and old‐growth forests are close to abandoned sites. The conservation value of a secondary forest is expected to increase over time, as species arriving from remaining old‐growth forest patches accumulate. Many studies are poorly replicated, which limits robust assessments of the number and abundance of old‐growth species present in secondary forests. Older secondary forests are not often studied and few long‐term studies are conducted in secondary forests. Available data indicate that both old‐growth and second‐growth forests are important to the persistence of forest species in tropical, human‐modified landscapes.     

Household Location Choices: Implications for Biodiversity Conservation

Abstract: Successful conservation efforts require understanding human behaviors that directly affect biodiversity. Choice of household location represents an observable behavior that has direct effects on biodiversity conservation, but no one has examined the sociocultural predictors of this choice relative to its environmental impacts. We conducted a case study of the Teton Valley of Idaho and Wyoming (U.S.A.) that (1) explored relationships between sociodemographic variables, environmental attitudes, and the environmental impact of household location choices, (2) assessed the potential for small household sizes in natural areas to multiply the environmental impacts of household location decisions, and (3) evaluated how length of residency predicted the environmental attitudes of people living in natural areas. We collected sociodemographic data, spatial coordinates, and land‐cover information in a survey of 416 households drawn from a random sample of Teton Valley residents (95% compliance rate). Immigrants (respondents not born in the study area) with the lowest education levels and least environmentally oriented attitudes lived in previously established residential areas in disproportionately high numbers, and older and more educated immigrants with the most environmentally oriented attitudes lived in natural areas in disproportionately high numbers. Income was not a significant predictor of household location decisions. Those living in natural areas had more environmental impact per person because of the location and because small households (<3 people/household) were 4 times as likely in natural areas as large households. Longer residency in natural areas predicted less environmentally oriented attitudes, suggesting that living in natural areas does not foster more concern for nature. Because populaces are rapidly aging, growing more educated, and potentially growing more environmentally oriented, these patterns are troubling for biodiversity conservation. Our results demonstrate a need for environmentalists to make household location decisions that reflect their environmental attitudes and future research to address how interactions between education level, environmental attitudes, population aging, and household location choices influence biodiversity conservation.     

Natural Die-Offs of Large Mammals: Implications for Conservation

The viability of populations is a central concern of biological conservation. The occurrence of catastrophic die-offs may greatly reduce the long-term viability of populations. Theoretical extinction models and viability analyses require information on the frequency of die-offs and on the distribution of die-off severities. A review of literature identified 96 natural die-offs in large mammal populations, with a die-off being defined as a peak-to-trough decline in estimated population numbers of at least 25%. If such die-offs are common, population viability analyses that ignore them may be overly optimistic. The severities of the natural die-offs of large mammals presented here are not uniformly distributed. There is a relative overabundance of die-offs in the 70–90% range, and an underabundance of die-offs greater than 90%. This may indicate the presence of buffers against population extinction. The reported causes of large mammal die-offs were significantly related to trophic level: herbivore die-offs were more often attributed to starvation, while carnivore die-offs were more often attributed to disease. Populations subject to large-scale phenomena such as drought and severe winters may not be protected from die-offs by population subdivision. On the other hand, populations subject to catastrophic disease epidemics may be protected by subdivision, and threatened by corridors between conservation areas and by translocation efforts.     

Exploited species impacts on trophic linkages along reef-seagrass interfaces in the Florida Keys

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.     

Local Population Dynamics in Metapopulation Models: Implications for Conservation

Abstract: Habitat fragmentation and the division of populations into spatially separated units have led to the increasing use of metapopulation models to characterize these populations. One prominent model that has served as a heuristic tool was introduced by Levins and is based on a collection of simplifying assumptions that exclude information on the dynamics and spatial distribution of local populations. Levins's and similar models predict the proportion of occupied habitat patches at equilibrium and the conditions needed to avoid total extinction. There are many obvious concerns about using such models, including how realistic alterations might change the predictions and whether occupancy has any relationship to population-level processes. Although many of the assumptions of these simple models are known to be unrealistic, we do not know how the assumptions affect model predictions. We simulated a metapopulation, and our results show that assumptions such as homogeneity of habitat patches, random migration among patches, equivalent extinction probabilities in all patches, and a large number of patches can lead to large overestimations of habitat occupancy. But when we explicitly modeled the underlying population dynamics within each patch, we found (1) that there was a strong correlation between proportion of occupied patches and total metapopulation size and (2) that the distribution of individuals among patches was relatively insensitive to model assumptions. Thus, our results show that although realistic modifications will change model predictions for occupancy, occupancy and population trends will be correlated. These correlations between occupancy and population size suggest that occupancy models may have some utility in conservation applications.     

Dynamics of larval fish assemblages over a shallow coral reef in the Florida Keys

Few time series collections have been made of the larval ichthyofauna in waters directly above shallow coral reefs. As a result, relatively little is known regarding the composition and temporal dynamics of larval fish assemblages in shallow-reef waters, particularly those near a major western boundary current. We conducted a series of nightly net tows from a small boat over a shallow reef (Pickles Reef) along the upper Florida Keys during four new moon and three third-quarter moon periods in July (two new moons), August, and September 2000. Replicate tows were made after sunset at 0–1 m and at 4–5 m depth to measure the nightly progression in community composition, differences in depth of occurrence, and abundance and diversity with lunar phase. A total of 66 families was collected over the 3-month period, with a mean (±SE) nightly density of 23.7±2.1 larvae per 100 m ³ and diversity of 24.2±0.9 taxa per tow. A total of 28.8% of the catch was composed of small, schooling fishes in the families Atherinidae, Clupeidae, and Engraulidae. Of the remaining catch, the top ten most abundant families included reef fishes as well as mangrove and oceanic taxa (in descending order): Scaridae, Blennioidei (suborder), Gobiidae, Paralichthyidae, Lutjanidae, Haemulidae, Labridae, Gerreidae (mangrove), Balistidae, and Scombridae (oceanic). These near-reef larval fish assemblages differed substantially from those collected during previous offshore collections. Taxa such as the Haemulidae were collected at a range of sizes and may remain nearshore throughout their larval period. Overall, the abundance and diversity of taxa did not differ with depth (although within-night vertical migration was evident) or with lunar phase. Temporal patterns of abundance of larval fish families clustered into distinct groups that in several cases paralleled family life-history patterns. In late July, a sharp shift in larval assemblages signaled the replacement of oceanic water with inner shelf/bay water. In general, the suite and relative abundance of taxa collected each night differed from those collected on other nights, and assemblages reflected distinct nightly events as opposed to constant or cyclical patterns. Proximity to the Florida Current likely contributes to the dynamic nature of these near-reef larval assemblages. Our results emphasize the uniqueness of near-reef larval fish assemblages and point to the need for further examination of the biophysical relationships generating event-related temporal patterns in these assemblages.     

Changes in barnacle population structure along an intertidal community gradient in the Florida Keys

Population distributions, densities and percentage deaths and individual size variations of the barnacles Chthamalus stellatus and Tetraclita squamosa, and the distribution of the vermetid snail Spirogluphus annulatus are measured to clarify determinants the Florida Keys (USA). The species composition of the pilings community and barnacle population densities correspond to physical gradients dependent on piling distance from shore. Interspecific competition for space is insignificant in determining C. stellatus presence or absence on pilings. Intraspecific crowding in highdensity zones of adult T. squamosa is evidenced by a significant decrease in basal diameter as density increases. The peak percentage of dead C. stellatus coincides with peak densities. The percentage of dead T. squamosa is at a low point at peak densities due to the ability of T. squamosa cyprids to settle and survive on adult shells in high-density regions. Feasible perturbation experiments for testing the importance of interspecific competition in determining the densities and vertical distributions of the species are discussed. The results of such experiments can be used to test the assumptions and predictions of the widely applied competition coefficient measure proposed by Levins (1968). Several theoretical deficiencies of Levins' measure are discussed.     

Genetic differentiation of bicolor damselfish (Eupomacentrus partitus) populations in the Florida Keys

Electrophoretic variation in proteins encoded by 23 loci revealed substantial genetic differentiation among populations of bicolor damselfish (Eupomacentrus partitus) collected from four coral reefs in the Florida Keys, USA, during 1986–1988. Genetic differentiation was concentrated between a sample collected from Little Grecian Rocks Reef (LGR) and the remaining samples, including fish from a reef only 600 m distant (Grecian Rocks Reef). Genetic distinction of the LGR sample derived from significantly heterogenous allelic frequencies at six of eight polymorphic loci. Aco-1 (aconitase); Ada (adenosine deaminase); Gpi-2 (glucosephosphate isomerase); Ldh-2 and Ldh-3 (lactate dehydrogenase); and Me-1 (malic enzyme); nevertheless, differentiation at cytosolic aconitase (Aco-1) far exceeded that observed for other loci (fixation index, F _ST=0.482), and differences in Aco-1 allele frequencies were largely responsible for large genetic distances (0.20) between LGR and the other reefs. Paradoxically, estimates of numbers of migrants exchanged between reefs per generation (mN _e=17.47) indicated the potential for extensive gene flow. The extent of genetic differentiation among these populations is evaluated relative to models of population genetic structure based on equilibrium between gene flow and natural selection or genetic drift.     

Redwood of the reef: growth and age of the giant barrel sponge Xestospongia muta in the Florida Keys

The growth of animals in most taxa has long been well described, but the phylum Porifera has remained a notable exception. The giant barrel sponge Xestospongia muta dominates Caribbean coral reef communities, where it is an important spatial competitor, increases habitat complexity, and filters seawater. It has been called the ‘redwood of the reef’ because of its size (often >1 m height and diameter) and presumed long life, but very little is known about its demography. Since 1997, we have established and monitored 12 permanent 16 m diameter circular transects on the reef slope off Key Largo, Florida, to study this important species. Over a 4.5-year interval, we measured the volume of 104 tagged sponges using digital images to determine growth rates of X. muta. Five models were fit to the cubed root of initial and final volume estimates to determine which best described growth. Additional measurements of 33 sponges were taken over 6-month intervals to examine the relationship between the spongocoel, or inner-osculum space, and sponge size, and to examine short-term growth dynamics. Sponge volumes ranged from 24.05 to 80,281.67 cm³. Growth was variable, and specific growth rates decreased with increasing sponge size. The mean specific growth rate was 0.52 ± 0.65 year⁻¹, but sponges grew as fast or slow as 404 or 2% year⁻¹. Negative growth rates occurred over short temporal scales and growth varied seasonally, significantly faster during the summer. No differences in specific growth rate were found between transects at three different depths (15, 20, 30 m) or at two different reef sites. Spongocoel volume was positively allometric with increasing sponge size and scaling between the vertical and horizontal dimensions of the sponge indicated that morphology changes from a frustum of a cone to cylindrical as volume increases. Growth of X. muta was best described by the general von Bertalanffy and Tanaka growth curves. The largest sponge within our transects (1.23 × 0.98 m height × diameter) was estimated to be 127 years old. Although age extrapolations for very large sponges are subject to more error, the largest sponges on Caribbean reefs may be in excess of 2,300 years, placing X. muta among the longest-lived animals on earth.