Conservation & Biodiversity
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Browsing Conservation & Biodiversity by Author "Calle, Leonardo"
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Item Anthropogenic food in the diet of the Sacred Ibis, Threskiornis aethiopicus, a non-native wading bird in southeastern Florida, USA(Florida Field Naturalist, 2011-03) Calle, Leonardo; Gawlik, Dale E.The Sacred Ibis ( Threskiornis aethiopicus ), is native to sub-Saharan Africa. A small breeding population in southeastern Florida, USA, was established in 1992 and expanded to surrounding natural areas until 2008 when an eradication program was initiated. This study investigated the degree to which the population of Sacred Ibis in South Florida consumes food items derived from human activities which may have contributed to its population expansion. Body measurements, the first such data for this species in North America, were obtained for eight adult males and five adult females. The contents of the esophageal tract and gizzards were used to classify ibis diets (N = 22) as being of anthropogenic origin (derived from human activities) if they contained cheese, meat, paper pulp, and/or pellet meal. The diet of the Sacred Ibis was comprised of predominately anthropogenic food items (58% of the cumulative biomass). Ibises with anthropogenic food items found in their diet consumed more biomass (26.99g ± SE 5.35g) than did birds that contained only natural food items in their diet (8.74g ± SE 2.21g). Natural diets, on average, contained a significantly greater percent vegetative matter (63% ± SE 12%) than did anthropogenic diets (8% ± SE 3%). Novel organic and inorganic items found in anthropogenic diets included bacon, glass, hot dog, pellet meal, and plastic. A cluster analysis revealed that some ibises used anthropogenic food as a primary food source whereas others used it as a supplement to natural food items. This study suggests that human food resources, and the habitats that contain them, may have the ability to support this species’ establishment. Further investigation, of ecologically similar species, may elucidate linkages between human food resources in urbanized areas and impacts in nearby natural habitats.Item Effects of tidal periodicities and diurnal foraging constraints on the density of foraging wading birds(American Ornithologists, 2016-07-01) Calle, Leonardo; Gawlik, Dale E.; Zhixiao, Xie; Green, Lauri; Lapointe, Brian; Strong, AllanIn intertidal zones, tidal cycles reduce water depths and provide areas of shallow water where wading birds can forage for aquatic prey (water depths 0–50 cm). However, a bird that forages diurnally can make use of only a portion of the tidal cycle, which can limit fulfillment of energetic demands. Furthermore, daily and biweekly (spring–neap) tides may compound effects on shallow-water availability for foraging birds. However, the relative effects of daily and biweekly tidal periodicities on the foraging ecology of wading birds are seldom investigated due to a lack of appropriate tools. Therefore, we developed a tidal simulation model to provide dynamic spatiotemporal estimates of the availability of water depths that are within the upper and lower bounds of the birds’ foraging water depth limits (‘‘shallow-water availability’’). We studied two wading bird species, the Little Blue Heron (Egretta caerulea), a daytime-only forager, and the Great White Heron (Ardea herodias occidentalis), which feeds both diurnally and nocturnally, to evaluate the relative effects of daily and biweekly tides on shallow-water availability and on patterns in abundance of foraging birds. Seasonal foraging surveys (n ¼ 38; 2011–2013) were conducted by boat along a 14-km transect adjacent to extensive intertidal flats in the lower Florida Keys, USA. For both species combined, biweekly tides resulted in a 0.61- to 6.09-fold change in abundance, whereas daily tides resulted in a 1.03- to 5.81-fold change in abundance. Diurnal shallow-water availability was not consistently correlated in magnitude or direction with spring–neap tidal cycles because differences in tide height between consecutive low tides were larger than changes in tidal amplitude from spring–neap tide cycles. Thus, the strong response by birds to the spring–neap tide was likely driven by mechanisms other than diurnal shallow-water availability aloneItem Evaluating temporal and spatial transferability of a tidal inundation model for foraging waterbirds(Ecosphere, 2022-04-03) Martinez, Marisa T.; Calle, Leonardo; Romañach, Stephanie S.; Gawlik, Dale E.For ecosystem models to be applicable outside their context of development, temporal and spatial transferability must be demonstrated. This presents a challenge for modeling intertidal ecosystems where spatiotemporal variation arises at multiple scales. Models specializing in tidal dynamics are generally inhibited from having wider ecological applications by coarse spatiotemporal resolution or high user competency. The Tidal Inundation Model of Shallow-water Availability (TiMSA) uniquely simulates tides to empirically derive a time-integrated measure of availability for a shallow-water depth range defined by the user. To evaluate temporal and spatiotemporal transferability, we employed TiMSA at the development site in the Florida Keys and at novel subsites in the Florida Bay (application site) under a different time period (application period). We used foraging little blue herons (Egretta caerulea) as the ecological unit with which to constrain the model's “water depth window,” that is, range of water depths to estimate shallow-water availability. At the development site, temporally consistent water depth windows contrasted with interannual variation in shallow-water availability, which revealed short-term changes in Little Blue Heron foraging habitat. At the application site, water depth accuracy varied by subsite and was correlated with spatial error in bathymetric elevation. Although TiMSA parameters were sensitive to environmental temporal variation and uncertainty in spatial data, a spatially explicit water depth window generated reliable estimates of shallow-water conditions over space and time at the development and application sites. By exploring the contributing factors to model error, we provide solutions to reduce uncertainty of TiMSA parameters at potential application sites and recommendations for addressing bathymetric inaccuracy in digital elevation models. Accurately quantifying spatiotemporal changes of shallow water has implications for monitoring habitat conditions for tidally influenced species and projecting future changes to coastal ecosystems in response to anthropogenic stressors and natural disturbances such as sea level rise.Item Relative effects of physical and small-scale nutrient factors on the distribution of tropical seagrasses in the Great White Heron National Wildlife Refuge, Lower Florida Keys(Elsevier B.V., 2015-03-26) Green, Lauri; Gawlik, Dale E.; Calle, Leonardo; Lapointe, Brian E.We tested the relative effects of physical factors such as exposure time and water depth as well as nutrient availability on Thalassia testudinum, Halodule wrightii and Syringodium filiforme distribution within the Great White Heron National Wildlife Refuge, Florida Keys. We quantified the percent cover of each sea- grass species in 1-m2 plots (n = 325) along intertidal and shallow subtidal flats adjacent to Upper Harbor Key Water Keys and Howe Key. We used model selection to evaluate the effects of physical parameters and water column nutrients on the percent cover and composition of seagrass species within plots. Best models were selected based on lowest Akaike’s information criteria (AIC) values and maximum model weights (ωi). We found that the presence of the other species, distance to nearest island and time of exposure during diurnal low tides best explained the distribution of T. testudinum (ωi = 0.44). Model averaged parameter estimates (ˇ) showed that H. wrightii and S. filiforme had the greatest negative influence on T. testudinum (ˇ = −0.396, −0.278, respectively). H. wrightii distribution was affected strongly by the presence of the other species, distance to Pine Channel, exposure time and mean lower low water (MLLW) (ωi = 0.56) with T. testudinum and S. filiforme exerting the greatest negative influences (ˇ = −0.450, −0.184, respectively). The best model indicated that S. filiforme was strongly influenced by the other species, distance to Pine Channel and MLLW (ωi = 0.5). Model averaging indicated that S. filiforme was associated with deep water (ˇMLLW = −28.0.018). Our study showcased that small scale (<100 m) habitat heterogeneity influenced the composition of seagrass communities.Item Time‐integrated habitat availability is a resource attribute that informs patterns of use in intertidal areas(Ecological Monographs, 2018-05-30) Calle, Leonardo; Green, Lauri; Strong, Allan; Gawlik, Dale E.In dynamic environments, resource availability may change by several orders of magnitude, over hours to months, but the duration of resource availability is not often included as a characteristic attribute of resources even though temporal resource dynamics might limit patterns of use. In our study of wading birds foraging in intertidal areas, tides cause large changes in the areal extent of shallow‐water foraging habitat (i.e., the resource), but tides also constrain the duration of availability, which is often overlooked. We hypothesized that temporal constraints on habitat availability from tides would be reflected in patterns of habitat use by foraging birds. We estimated the time‐integrated habitat availability and compared it to traditional habitat attributes (seagrass cover, substrate type, instantaneous water depth, and proximity to mangrove islands or deep water) that have strong evidential support for influencing patterns of use. To evaluate our hypotheses, we quantified habitat attributes at intertidal areas in the Florida Keys, USA, where wading birds were observed foraging (Little Blue Heron, Egretta caerulea: N = 183; Great White Heron, Ardea herodias occidentalis: N = 162). We tested for nonrandom use by sampling habitat attributes at two spatial scales around the observed feeding locations and we analyzed the data using a conditional logistic regression model. There was no evidence that seagrass cover or substrate explained patterns of use. The proximity of foraging locations relative to mangroves and to deep water were important at both spatial scales but had lower effect sizes (odds ratios) than time‐integrated habitat availability and water depth, and the latter may only serve as a physical constraint on access. We found support that time‐integrated habitat availability was a distinct resource attribute, had the greatest effect size (four‐ to eightfold change in relative probability of use), and best explained patterns of habitat use at the largest spatial scale. In studies of resource use where changes in resource availability are nonlinear or when strong constraints on access are imposed by behavior, incorporating time‐integrated estimates of resource availability into analyses can improve insights into spatiotemporal patterns of resource use.