DOI: 10.5061/dryad.76hdr7swx
title: Complex multi-predator effects on demographic habitat selection and community assembly in colonizing insects

description: Running the gauntlet of predators consumes critical time and energy
 resources, as all species are vulnerable to one or, typically, more
 predators at some life stage. Prey employ a vast array of mechanisms to
 avoid predation, and predators, likewise, come in a bewildering variety.
 Thus, defensive adaptations are rarely one size fits all. Considerable
 work has addressed multi-predator consumptive effects, but we now know
 that non-consumptive effects of predators can dramatically impact
 individuals, (meta)populations, and (meta)communities. However, little is
 known regarding the community-wide dynamics of non-consumptive effects
 generated by multiple predators. Predator avoidance by choosing a patch
 that is free of a particular predator or predators can be the most
 effective strategy if conditions at colonization are a reliable predictor
 of absence, which is often true for fish in freshwater systems. We
 experimentally manipulated composition of the predator assemblage in
 aquatic mesocosms in a substitutive design, with zero, one, two, or three
 caged predatory fish species (one benthic, one pelagic, and one surface
 fish) at constant density and biomass, and assayed responses of naturally
 colonizing aquatic insects. We addressed three related questions; first,
 how do members of a diverse assemblage of colonizing aquatic insects
 respond to this variation in species and species combinations, second, do
 individual species (and higher taxa), respond differently to single vs
 multiple predator species (species richness), and third how do any
 responses to fish species and species combinations, and effects on species
 richness, translate into community-wide changes in the composition of
 colonists. Prey had varied responses to specific predators or combinations
 of predators, resulting in distinct community composition across
 treatments and higher β-diversity with predators. Prey showed emergent
 multi-predator effects, where certain species only responded to predator
 species combinations, but not to any individual predator, and stronger
 effects of multiple predator vs single predator treatments, despite strong
 responses to individual predators in many taxa. Habitat selection effects
 can range from the individual to the metacommunity, and the dynamics of
 habitat selection in response to predators is a complex function of
 predator identity, density, richness, species composition, and patch
 spatial context.
description: Materials and
 Methods Our experiment was
 conducted in a large oldfield at the University of Mississippi Field
 Station (UMFS), Lafayette County, MS. There is a diverse assemblage of
 aquatic insects at UMFS, including 132 species of aquatic beetles and over
 40 species of aquatic hemipterans (Pintar and Resetarits 2020a, 2020b). We
 set up five arrays (blocks), each with nine, 1300 L (surface area = 2.54
 m<sup>2</sup>) cylindrical mesocosms (N=45) laid out in
 isosceles trapezoids (Figs. 1a, Appendix 1: Fig. S1).  We crossed the
 presence/absence of three species of fish: golden topminnows
 (<i>Fundulus chrysotus</i>), golden shiners
 (<i>Notemigonus crysoleucas</i>), and brown madtoms
 (<i>Noturus phaeus</i>) (Fig. 1b), which are among the most
 commonly encountered species at UMFS.  Each species represents a different
 habitat/foraging strategy. <i>Notemigonus crysoleucas</i> is a
 small, pelagic, omnivorous-planktivorous, gape-limited fish that is
 widespread and abundant in both lentic and lotic habitats (Lee et al.
 1980). <i>Fundulus chrysotus</i> is a small, gape-limited,
 surface-feeding topminnow and is also widespread and abundant (Lee et al.
 1980). <i>Noturus phaeus</i> is a small, benthic foraging
 catfish typically found in lotic habitats (Lee et al. 1980, Chan and
 Parsons 2000), though is also common in overflow pools, backwaters, slow
 moving wetlands, and ponds that flood, including those at UMFS (pers.
 obs.); it is least gape-limited of the three. 
 We began filling
 mesocosms with well-water on 11 May 2017, one block at a time, completing
 filling on 13 May, at which point 1 kg aliquots of mixed, dried leaf
 litter (mixed hardwoods) were added to each mesocosm. Mesocosms were very
 quickly colonized by zooplankton and numerous small dipterans whose adults
 and/or eggs/larvae can pass through the screens (1.3 x 1.13 mm mesh),
 providing the fish a resource base. The high overall survival rate and
 positive growth of all three fish species supports the presence of an
 adequate food base. On 14 May each patch received 6 fish: 6/species in
 single predator treatments, 3/3 in two predator treatments, and 2/2/2 in
 three predator treatments, plus fishless controls. Density is on the lower
 end of biomass density in previous experiments and natural ponds, but
 above the threshold eliciting avoidance in many aquatic insects and
 treefrogs (Rieger et al. 2004; unpubl. data). To equalize biomass among
 fish treatments within blocks, we created complementary (1 “large,” 1
 “small”) pairs within each of the three species for each block (by eye to
 minimize stress), and randomly assigned the appropriate number of pairs to
 each fish treatment patch within that block, maintaining the same density,
 approximate biomass, and size-structure across patches within blocks. On
 15 May the experiment was begun by submerging screen lids to allow
 efficient collection of insects, and to separate fish from colonists,
 obviating consumptive effects (Appendix 1: Fig. S1). Dead fish (18/210)
 were replaced until 20 May, after which there was no observed mortality.
 Insects were collected weekly from 22 May until 20 November, with one
 final collection on 8 December, and preserved for later identification.
 Insect colonization is not responsive to either intra- or interspecific
 density, even when insects are not removed weekly (Pintar and Resetarits
 2020c), and predation among adult insects is limited to predation by
 <i>Notonecta irrorata</i> on certain beetles, which always
 results in decapitation (Pintar and Resetarits 2021). There was no
 evidence of predation in this experiment, and<i> N.
 irrorata</i> occurred in only 77/1260 samples (97 individuals). We
 have not observed any terrestrial or avian predators at our cattle tanks
 across dozens of experiments. Insect identification
 followed Pintar and Resetarits (and sources therein) (Pintar and
 Resetarits 2020b, 2020a). Only members of the genus
 <i>Sigara</i> (primarily <i>S. pectenata </i>at
 UMFS) and <i>Paracymus</i> (primarily <i>P. subcupreus
 </i>at UMFS) were not all identified to species. Fish survival from
 20 May to 8 December was 91% across all three species: 89% for <i>F.
 chrysotus</i>, 94% for <i>N. phaeus</i>, and 91% for
 <i>N. crysoleucas</i>. Distribution of mortality was such that
 only two patches did not hold their full treatment until the end of the
 experiment; one <i>F. chrysotus</i>×<i>N.
 phaeus</i> (FC×NP) patch had no surviving <i>F.
 chrysotus</i>, and one three predator patch (X3) also had no
 surviving <i>F. chrysotus</i>. We could not track fish
 survival during the experiment, so we cannot determine when mortality
 occurred. Since neither tank was and outlier or otherwise out of the
 ordinary, our assumption was that these tanks held their respective
 treatments for much of the experiment. Given the overall low fish
 mortality, this is not unreasonable<i>. </i>Thus, we included
 both in the final analyses to maintain the balanced design required for
 independent estimates of multivariate community location and dispersion
 using PERMANOVA and PERMDISP (see below, Anderson and Walsh
 2013).
description: See details in excel file.