Time‐integrated habitat availability is a resource attribute that informs patterns of use in intertidal areas

Abstract

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.

Use of Our Future Seas: Relevance of Spatial and Temporal Scale for Physical and Biological Indicators

“…It is evident that changes in the population dynamics of higher trophic levels are likely to reflect those of their preferred prey, which may, in turn, be bottom-up driven by dynamic biophysical oceanographic processes across spatial and temporal scales (Shealer, 2002;Bertrand et al, 2014;Boyd et al, 2015;Woodson and Litvin, 2015;McInnes et al, 2017;Cox et al, 2018; Figure 5). For example, on a local scale, by accounting for the influence of tidal state and stratification on foraging habitat, seabird-fish interactions were identified, highlighting that critical marine habitats occur at limited spatial locations but also within specific temporal intervals (Cox et al, 2013;Calle et al, 2018). The extent to which spatial and tidal temporal oceanographic features are important to seabirds is dependent on the use of such features by their prey (Daunt et al, 2006;Stevick et al, 2008;Heim et al, 2019).…”

Great egret (Ardea alba) habitat selection and foraging behavior in a temperate estuary: Comparing natural wetlands to areas with shellfish aquaculture

“…relative selection of shellfish aquaculture areas did not exceed that for natural wetlands at any water depth. Great egrets appear quite capable of ascertaining the relative benefits and costs of foraging in different areas that result from variance in prey density, prey capturability, and competition [16,54,55]. Generally, the density of foraging great egrets is greatest when water depths are between 20-40 cm [9].…”

“…daily and weekly tide patterns and seasonal climatic patterns) and act to concentrate prey [18,[56][57][58]. In tidal systems in southern Florida, time-integrated habitat availability (due to tidal cycles) was the resource attribute with the strongest effect on probability of use by wading birds across all habitats investigated [54]. The intertidal and shallow subtidal areas of Tomales Bay are characterized by subtle heterogeneity in the substrate surface, and egrets foraging above the tide line often seem to be focusing on small tidal puddles (pers.…”

A general model of temporary aquatic habitat use: Water phenology as a life history filter

“…Sometimes, small‐bodied fish using TAHs for one purpose (e.g., spawning) are closely followed by predatory fish to eat them (McFarland, Wipfli, & Whitman, , Figure ). This is also true in the intertidal zone, where prey fishes take refuge from open water leading to a distributional shift that is tracked by predatory fishes and avian predators (Calle, Green, Strong, & Gawlik, ; Gibson, ). Many well‐known and recreationally important fish species such as bonefish ( Albula vulpes , Albulidae) and permit ( Trachinotus falcatus , Carangidae) regularly access inundated tidal flats with the incoming tide to forage (Murchie et al, ).…”

“…Such stranding events are known to occur in the Parana River system of South America, where an estimated 40,000 tonnes of fish are stranded each year (Bonetto, Dioni, & Pignalberi, 1969). Even if not leading to stranding, TAHs that benefit fishes most (e.g., ones with long durations or ones that are predictable) may lead to equally high use by predators that also select habitat according to duration of resource availability (Calle et al, 2018).…”