David R. Breininger

SETTING RELIABILITY BOUNDS ON HABITAT SUITABILITY INDICES

We expressed quantitative and qualitative uncertainties in suitability index functions as triangular distributions and used the mechanics of fuzzy numbers to solve for the distribution of uncertainty around the habitat suitability indices derived from them. We applied this approach to a habitat model for the Florida Scrub-Jay. The results demonstrate that priorities and decisions associated with management and assessment of ecological systems may be influenced by an explicit consideration of the reliability of the indices.

TERRITORY QUALITY TRANSITIONS AND SOURCE–SINK DYNAMICS IN A FLORIDA SCRUB‐JAY POPULATION

Source–sink theory provides an approach to identify habitat arrangements needed to sustain populations in spatially and temporally varying landscapes. Our objective was to investigate whether source–sink ideas could be applied to quantify how habitat arrangements influenced Florida Scrub-Jay (Aphelocoma coerulescens) population dynamics, in order to enhance habitat restoration. From 1988 to 2001, we measured reproductive success, survival, immigration, emigration, pair bond fidelity, and the duration of delayed breeding by young. The arrangement of shrub height in each territory was used to classify habitat quality each year, according to the following categories: short ( 170 cm), and tall (>170 cm). Annual demographic performance rates were calculated in each territory by summing the recruitment of potential breeders (the number of yearlings produced) and then subtracting the number of breeders that died. The mean demographic performance per breeding pair was −0.57, 0.33, −0.26, and −0.35, respectively, for short, optimal, tall mix, and tall territories. Optimal territories functioned as sources because recruitment exceeded mortality; hence, the optimal territories were net exporters to marginal habitat. Potential breeders were exported to sink territories by active dispersal and by “territory quality transitions,” whereby territories produced an excess of potential breeders while in optimal condition and then became marginal because of shifting territory boundaries and habitat conditions. Short, tall mix, and tall territories functioned as sinks because they were net importers, mortality exceeded recruitment, and because there were no density-dependent reductions in their demographic performance. The population declined because there were too few optimal territories to offset declines in sinks, which usually had too much tall scrub even though most of the landscape had been burned recently. Successful habitat restoration requires greater emphases on improving habitat quality at the territory scale because this is the fundamental landscape unit related to demography. Source–sink ideas, complemented by territory quality transitions, provide a quantitative approach to directly relate habitat and demographic objectives. Corresponding Editor: D. J. Levey.

Coupling past management practice and historic landscape change on John F. Kennedy Space Center, Florida

Historic landcover dynamics in a scrubby flatwoods (Tel-4) and scrub landscape (Happy Creek) on John F. Kennedy Space Center were measured using aerial images from 1943, 1951, 1958, 1969, 1979, and 1989. Landcover categories were mapped, digitized, geometrically registered, and overlaid in ARC/INFO. Both study sites have been influenced by various land use histories, including periods of range management, fire suppression, and fire management. Several analyses were performed to help understand the effects of past land management on the amount and spatial distribution of landcover within the study sites. A chi-squared analysis showed a significant difference between the frequency of landcover occurrence and management period. Markov chain models were used to project observed changes over a 100-year period; these showed current management practices being effective at Tel-4 (restoring historic landscape structure) and much less effective at Happy Creek. Documenting impacts of past management regimes on landcover has provided important insight into current landscape composition and will provide the basis for improving land management on Kennedy Space Center and elsewhere.

FLORIDA SCRUB-JAY DEMOGRAPHY AND DISPERSAL IN A FRAGMENTED LANDSCAPE

I measured population dynamics and cooperative breeding in an isolated population of Florida Scrub-Jays (Aphelocoma coerulescens) on an urban barrier island in southern Brevard County, Florida. In 1992, the scrub-jay population consisted of 29 breeding pairs within six population clusters that comprised two subpopulations. By 1998, the pop- ulation declined to 10 pairs in four clusters because of poor reproductive success. The fre- quency of breeding by one-year-olds was related to the availability of breeding vacancies that increased as the population declined. Nearly half of the breeding vacancies were filled

Waterbird use of coastal impoundments and management implications in east-central Florida

Monthly surveys were conducted on Kennedy Space Center for one year to determine densities of waterbirds within impounded salt marshes that were predominantly open water with little emergent vegetation. The objective was to assess the importance of these impoundments to waterbirds, particularly wading birds, which are species of special conservation concern. Water-level management for mosquito control and waterfowl provided habitat for an abundance of ducks, shorebirds, coots, and wading birds. Average densities throughout the year for these groups were 5.26, 4.12, 2.80, and 2.20 birds/ha, respectively. The majority of waterfowl were present during the winter. Shorebirds were most common during spring migration. Wading bird densities increased with declining water level. Due to the extensive alteration and development of coastal wetlands in central Florida, properly managed impoundments may provide important feeding areas for maintaining certain waterbird populations.

Estimating Occupancy of Gopher Tortoise (Gorpherus polyphemus) Burrows in Coastal Scrub and Slash Pine Flatwoods

One hundred twelve plots were established in coastal scrub and slash pine flatwoods habitats on the John F. Kennedy Space Center (KSC) to evaluate relationships between the number of burrows and gopher tortoise (Gopherus polyphemus) density. All burrows were located within these plots and were classified according to tortoise activity. Depending on season, bucket trapping, a stick method, a gopher tortoise pulling device, and a camera system were used to estimate tortoise occupancy. Correction factors (% of burrows occupied) were calculated by season and habitat type. Our data suggest that <20% of the active and inactive burrows combined were occupied during seasons when gopher tortoises were active. Correction factors were higher in poorly-drained areas and lower in well-drained areas during the winter, when gopher tortoise activity was low. Correction factors differed from studies elsewhere, indicating that population estimates require correction factors specific to the site and season to accurately estimate pop- ulation size.

Gopher Tortoise (Gopherus polyphemus) Densities in Coastal Scrub and Slash Pine Flatwoods in Florida

Densities of gopher tortoises were compared with habitat characteristics in scrub and in flatwood habitats on the Kennedy Space Center, Florida. Tortoises were distributed widely among habitat types and did not have higher densities in well-drained (oak-palmetto) than in poorly-drained (saw palmetto) habitats. Fall densities of tortoises ranged from a mean of 2.7 individuals/ha in disturbed habitat to 0.0 individuals/ha in saw palmetto habitat. Spring densities of tortoises ranged from a mean of 2.5 individuals/ha in saw palmetto habitat to 0.7 individuals/ha in oak-palmetto habitat. Densities of tortoises were correlated positively with the percent herbaceous cover, an indicator of food resources. Plots were divided into three burn classes; these were areas burned within three years, burned four to seven years, and unburned for more than seven years prior to the study. Relationships between densities of tortoises and time-since-fire classes were inconsistent.

Metapopulation dynamics of the california least tern

The California least tern (Sterna antillarum browni) is federally listed as an endangered species. Its nesting habitat has been degraded, and many colony sites are vulnerable to predation and human disturbance. We examined a metapopulation model for the California least tern that can be used to predict persistence of populations along the Pacific coast and the effects of various management actions. We used the model to estimate the effect of reducing predation impact, an important source of reduced fecundity, in various populations. Apart from restricting human access to nesting sites, most management efforts have concentrated on predation. In the model, each cluster of nearby colonies is defined as a population. Within each population, the model includes age-structure, year-to-year changes in survival and fecundity, regional catastrophes (strong El Nino/Southern Oscillation [ENSO] events), and local catastrophes (reproductive failure due to predation). The model predicted a continuing population increase and a low risk of substantial decline over the next 50 years. However, this prediction was sensitive to assumptions about survival and fecundity. Under a pessimistic scenario, the model predicted a high risk of decline, although a low risk of extinction. We simulated the effect of predator management by reducing the probability of reproductive failure due to predation. The improvement in viability ranged from 1% to 4% for single populations and up to 8% when all populations were included. Results indicated that the number and location of populations selected for focused management influenced the effectiveness of management efforts.

DO HABITAT POTENTIAL, POPULATION DENSITY, AND FIRES INFLUENCE SCRUB‐JAY SOURCE–SINK DYNAMICS?

The concept of source and sinks can guide conservation, but empirical studies are needed to demonstrate that this concept applies to the real world. We investigated whether the source–sink concept could help to clarify the influence of habitat potential (scrub ridge characteristics), population density, and fires (shrub heights) on Florida Scrub-Jay (Aphelocoma coerulescens) demography and dispersal. We mapped territories and measured survival, recruitment, emigration, immigration, and shrub heights annually for 12 years. We classified territories as oak if they overlapped well-drained ridges, oak–palmetto if they overlapped poorly drained ridges >0.4 ha, and palmetto–oak if they only overlapped poorly drained ridges <0.4 ha. Territory size differed little among these categories but was negatively correlated with the annual number of breeding pairs, which ranged from 12 to 27. Scrub ridge characteristics influenced the locations of sinks and potential sources, whereas population density and fires caused t...

Relationships between Fire and Bird Density in Coastal Scrub and Slash Pine Flatwoods in Florida

-Bird densities within coastal scrub and slash pine flatwoods were compared with time since fire, mean shrub height, number of snags and percent burn. Most shrubdwelling birds preferred older stands (>10 yr since last fire) with taller shrubs, or intermediate stands (4 yr since last fire) than recently burned stands (1-2 yr since last fire). Five species were negatively correlated with percent burn in stands burned 1-2 yr previously. The downy woodpecker was most abundant in recently burned areas. Densities of three species of woodpeckers and the northern bobwhite were positively correlated with snag density. The results suggest that extensive burns occurring every 4 yr or less are likely to have a negative influence on shrub-dwelling birds that are a natural component of these coastal communities.