Predation risk and patch size jointly determine perceived patch quality in ovipositing treefrogs, Hyla chrysoscelis

Abstract

Two of the most important factors determining community structure and diversity within and among habitat patches are patch size and patch quality. Despite the importance of patch size in existing paradigms in island biogeography, metapopulation biology, landscape ecology, and metacommunity ecology, and growing conservation concerns with habitat fragmentation, there has been little investigation into how patch size interacts with patch quality. We crossed three levels of patch size (1.13 m , 2.54 m and 5.73 m ) with two levels of patch quality (fish presence/absence, green sunfish [Lepomis cyanellus] and golden shiners [Notemigonus crysoleucus]) in six replicate experimental landscapes (3 × 2 × 6 = 36 patches). Both fish predators have been previously shown to elicit avoidance in ovipositing treefrogs. We examined how patch size and patch quality, as well as the interaction between size and quality, affected female oviposition preference and male calling site choice in a natural population of treefrogs (Hyla chrysoscelis). Females almost exclusively oviposited in the largest fishless patches, indicating that females use both risk, in the form of fish predators, and size itself, as components of patch quality. Females routinely use much smaller natural and experimental patches, suggesting that the responses to patch size are highly context dependent. Responses to fish were unaffected by patch size. Male responses largely mimicked those of females, but did not drive female oviposition. We suggest that patch size itself functions as another aspect of patch quality for H. chrysoscelis, and serves as another niche dimension across which species may behaviorally sort in natural systems. Because of strong, shared avoidance of fish (as well as other predators), among many colonizing taxa, patch size may be a critical factor in species sorting and processes of community assembly in freshwater habitats, allowing species to behaviorally segregate along gradients of patch size in fishless ponds. Conversely, lack of variation in patch size may concentrate colonization activity, leading to intensification of species interactions and/or increased use of lesser quality patches.

Differential oviposition and offspring success of gray treefrogs in the presence of an invasive fish

“…For example, H. chrysoscelis and H. squirella only oviposited in mesocosms with fish on nights when the most eggs were laid Resetarits 2003, 2008). These results contrast with who found that when given a choice among ponds with G. affinis, conspecific eggs, or both G. affinis and conspecific eggs, P. triseriata did not differentiate among the three types of ponds and Resetarits et al (2018) who found no effect of conspecific density on oviposition by H. chrysoscelis in the presence of fish.…”

“…When eggs were removed daily, Hyla chrysoscelis and Hyla squirella only oviposited in the presence of a fish predator on nights with the highest breeding activity Resetarits 2003, 2008). In contrast, Resetarits et al (2018) found no evidence of conspecific density affecting the avoidance of ponds with fish in H. chrysoscelis, but eggs were removed daily for the first 31 d of the 71-d experiment (44% of the experiment). However, the prediction of a shift in oviposition site selection has not been directly tested since in these previous studies, eggs have been removed in the experimental habitats soon after they were deposited for much or all of the duration of the experiment.…”

“…() who found that when given a choice among ponds with G. affinis , conspecific eggs, or both G. affinis and conspecific eggs, P. triseriata did not differentiate among the three types of ponds and Resetarits et al. () who found no effect of conspecific density on oviposition by H. chrysoscelis in the presence of fish.…”

Precipitation-dependent source–sink dynamics in a spatially-structured population of an outbreaking caterpillar

“…Considering that predators can cause local extinctions (Weisser 2000;van Nouhuys and Hanski 2002), determining patch quality through bottom-up studies alone (i.e., laboratory feeding assays or in situ caging experiments, where predators are excluded) could lead to erroneous conclusions. Moreover, because predators can affect colonization decisions, incomplete understanding of top-down influences could obscure the relative importance of local and regional processes (Shurin 2001;Kneitel and Miller 2003;Grainger et al 2017;Resetarits et al 2018).…”

“…Less common proxies are top-down factors. Often considered separately from patch quality, the presence of predators can influence the establishment or persistence of species in a patch (Shurin 2001;Kneitel and Miller 2003;Grainger et al 2017) or deter colonization processes (i.e., habitat selection and immigration; Resetarits et al 2018). The utility of using these proxies is contingent upon the strength of the relationship between the quantifiable dependent variable and actual patch quality.…”