Inter‐patch connectivity and intra‐patch structure differentially alter prey consumption by multiple predators

Abstract

Citation: Pitcher, K. A., and D. A. Soluk. 2016. Inter-patch connectivity and intra-patch structure differentially alter prey consumption by multiple predators. Ecosphere 7(11):e01598. 10.1002/ecs2.1598 Abstract. Structural habitat complexity (SHC) and functional habitat connectivity (FHC) have important effects on predator-prey interactions and exert a strong influence on community structure/dynamics in terrestrial and aquatic ecosystems. Although these factors vary simultaneously in most systems, their interactive effects are poorly understood. Using artificial pond mesocosms and multiple prey types, we manipulated plant density (SHC: low, high) and inter-patch distance (FHC: short, long) in a full factorial design to test for potential interactive effects of these factors on competition and predation by a dragonfly larva (Anax junius) and fish predator (Lepomis cyanallus). When inter-patch distances (FHC) were short, A. junius consumed more amphipods (36% AE 4.6%) compared with long treatments (19% AE 4.8%). We detected no significant effects of plant density (SHC) on prey consumption by A. junius. There were significant interactive effects of FHC and SHC on Lepomis cyanellus consumption of amphipods and damselflies. The most counterintuitive of these effects was that sunfish consumed more larval damselflies at high plant density (64% AE 6.0%) than at low plant density (38% AE 8.6%) but only in short connection treatments. This interactive effect of SHC and FHC on damselfly predation by L. cyanellus was likely because damselflies exhibited riskier behavior at higher SHC. Prey consumption with both predators present was additive, but no significant effect of either SHC or FHC on interspecific predation was detected, suggesting compensatory foraging responses. Structural habitat complexity and FHC interactively influence predator foraging behavior in complex, non-intuitive ways that are highly dependent on the predator/prey combination in question. Structural habitat complexity and FHC are currently being influenced by anthropogenic factors in multiple ways (e.g., habitat loss, global climate change), and being able to predict the responses of biotic communities to these changes should be an important consideration in restoration and conservation efforts.

Fish presence and inter‐patch connectivity interactively alter the size of emergent insects in experimental enclosures

“…). Several studies show that increased SHC, both in the field and in mesocosms, can reduce predation by fish on larval insects within aquatic ecosystems (Crowder and Cooper , Diehl , Pitcher and Soluk ). The lack of an effect of SHC on emergent insect biomass in our study was most likely due to noticeable and qualitatively similar algal surface cover within the enclosures that likely provided additional SHC and thus diminished the impact of any differences in the stem density treatments.…”

“…The indirect effects of FHC on the size of emergent damselflies in treatments with fish likely result from the direct effects of FHC on the movement of fish between habitat patches. In a previous study, we reported that green sunfish actively use PVC pipe connectors of the same lengths and diameter to move between enclosures, making an average of 7–17 crosses per hour (Pitcher and Soluk ). Although the initial difference in travel distance between the two connection lengths appears relatively small (1.22 m vs. 0.30 m), the high frequency of movement through them can quickly result in large differences in total distance travelled over time.…”

“…Thus, these systems provide an optimal model for testing the influence that local‐level spatial complexity has on the export of prey resource subsidies (Welborn et al. , Williams , Pitcher and Soluk ). Using a manipulative enclosure design, we evaluate how SHC and FHC in semi‐permanent ponds alter prey resource subsidies (i.e., emergent insects) moving from aquatic to terrestrial ecosystems.…”

“…Both SHC and FHC can alter the way predators impact prey populations independently, or their effects can combine to generate complex interactive effect. Increased plant stem densities (SHC) and increased inter-patch distances (FHC) decrease predation by providing increased refugia for prey (Crowder and Cooper 1982, Gilinsky 1984, Lewis and Eby 2002, Pitcher and Soluk 2016. They can also increase biodiversity by allowing more species to coexist within habitats (Briers and Warren 1999, Finke and Denno 2002, Hampton 2004, Warfe and Barmuta 2006.…”

“…Interactive effects of SHC and FHC on predator-prey dynamics also occur. For example, the negative relationship between plant stem densities (SHC) and predator consumption rates can be reversed when inter-patch distances (FHC) are shortened (Pitcher and Soluk 2016), possibly because prey are more willing to take risks (e.g., forage and emerge) in higher stem densities, but do not respond to the increased risk of predator visitation caused by shorter inter-patch distance (Pitcher and Soluk 2016).…”