Variation in phenology and density differentially affects predator–prey interactions between salamanders

Abstract

Variation in the timing of breeding (i.e., phenological variation) can affect species interactions and community structure, in part by shifting body size differences between species. Body size differences can be further altered by density-dependent competition, though synergistic effects of density and phenology on species interactions are rarely evaluated. We tested how field-realistic variation in phenology and density affected ringed salamander (Ambystoma annulatum) predation on spotted salamanders (Ambystoma maculatum), and whether these altered salamander dynamics resulted in trophic cascades. In outdoor mesocosms, we experimentally manipulated ringed salamander density (low/high) and breeding phenology (early/late) of both species. Ringed salamander body size at metamorphosis, development, and growth were reduced at higher densities, while delayed phenology increased hatchling size and larval development, but reduced relative growth rates. Survival of ringed salamanders was affected by the interactive effects of phenology and density. In contrast, spotted salamander growth, size at metamorphosis, and survival, as well as the biomass of lower trophic levels, were negatively affected primarily by ringed salamander density. In an additional mesocosm experiment, we isolated whether ringed salamanders could deplete shared resources prior to their interactions with spotted salamanders, but instead found direct interactions (e.g., predation) were the more likely mechanism by which ringed salamanders limited spotted salamanders. Overall, our results indicate the effects of phenological variability on fitness-related traits can be modified or superseded by differences in density dependence. Identifying such context dependencies will lead to greater insight into when phenological variation will likely alter species interactions.

Optimal reproductive phenology under size‐dependent cannibalism

“…The colonization of habitats and arrival times of species or offspring in a seasonal environment is important in predator–prey interactions and in forming the structure of communities (Anderson, Rowland, & Semlitsch, 2017; De Meester, Vanoverbeke, Kilsdonk, & Urban, 2016; Rasmussen, Van Allen, & Rudolf, 2014; Salamolard, Butet, Leroux, & Bretagnolle, 2000; Shulman et al, 1983; Sniegula, Golab, & Johansson, 2019). For instance, a large difference in arrival times of nymphs of two dragonfly species causes the exclusion of a late arrival species (Rasmussen et al, 2014).…”

Optimal reproductive phenology under size-dependent cannibalism

“…The colonization of habitats and arrival times of species in a seasonal environment is important in predator-prey interactions and in forming the structure of communities [5][6][7][8]. This is known as priority effects, which emphasize how the sequence of breeding or other phenologies determine interaction strength.…”

Impacts of phenological variability in a predatory larval salamander on pond food webs

“…Larvae overwinter in ponds, and metamorphose in the late spring and early summer (Hocking et al , ; Semlitsch et al , ). Thus, A. annulatum larvae are typically large enough to be a top predator on aquatic stages of spring‐breeding amphibians (Anderson & Semlitsch, ; Anderson et al , ; Anderson, Rowland & Semlitsch, ). This is important because A. annulatum are sympatric with at least six anurans and two other caudates at our collection sites (Semlitsch et al , ).…”

“…We hypothesized that greater variability in breeding phenology of the ringed salamander ( Ambystoma annulatum , Cope 1886) would increase cannibalism rates among larvae due to greater body size variability (Nyman, Wilkinson & Hutcherson, ; Petranka & Thomas, ), and ultimately result in increased body size at metamorphosis, a correlate of future adult fitness (Semlitsch, Scott & Pechmann, ; Scott, ; Earl & Whiteman, ). Because A. annulatum are a top predator of spring‐breeding amphibians (Anderson & Semlitsch, ; Anderson et al , ; Anderson, Rowland & Semlitsch, ), we also predicted that when more cannibalism occurred, the reduced number of salamander larvae would have less of an impact on the anuran community, resulting in greater amphibian diversity. Lastly, we expected that greater cannibalism in A. annulatum from increased breeding variability would cascade to other trophic levels, that is higher abundances of zooplankton due to decreased predation pressure and subsequently lower biomass of periphyton, the zooplankton and anuran food resource.…”