DOI: 10.5061/dryad.h70rxwdrg
title: Trophic cascade within and across ecosystems: the role of anti-predatory defenses, predator type, and detritus quality

description: Species in one ecosystem can indirectly affect multiple biodiversity
 components and ecosystem functions of adjacent ecosystems. The magnitude
 of these cross-ecosystem effects depends on the attributes of the
 organisms involved in the interactions, including traits of the predator,
 prey and basal resource. However, it is unclear how predators with
 cross-ecosystem habitat interact with predators with single-ecosystem
 habitat to affect their shared ecosystem. Also, unknown is how such
 complex top-down effects may be mediated by the anti-predatory traits of
 prey and quality of the basal resource. We used the aquatic invertebrate
 food webs in tank bromeliads as a model system to investigate these
 questions. We manipulated the presence of a strictly aquatic predator
 (damselfly larvae) and a predator with both terrestrial and aquatic
 habitats (spider) and examined effects on survival of prey (detritivores
 grouped by anti-predator defense), detrital decomposition (of two plant
 species differing in litter quality), nitrogen flux and host plant growth.
 To evaluate the direct and indirect effects of each predator type on
 multiple detritivore groups and ultimately on multiple ecosystem
 processes, we used piecewise structural equation models. For each response
 variable, we isolated the contribution of different detritivore groups to
 overall effects by comparing alternate model formulations. Alone,
 damselfly larvae and spiders each directly decreased survival of
 detritivores and caused multiple indirect negative effects on detritus
 decomposition, nutrient cycling, and host plant growth. However, when
 predators co-occurred, the spider caused a negative non-consumptive effect
 on the damselfly larva, diminishing the net direct and indirect top-down
 effects on the aquatic detritivore community and ecosystem functioning.
 Both detritivore traits and detritus quality modulated the strength and
 mechanism of these trophic cascades. Predator interference was mediated by
 undefended or partially defended detritivores as detritivores with
 anti-predatory defenses evaded consumption by damselfly larvae but not
 spiders. Predators and detritivores affected ecosystem decomposition and
 nutrient cycling only in the presence of high-quality detritus, as the
 low-quality detritus was consumed more by microbes than invertebrates. The
 complex responses of this system to predators from both recipient and
 adjacent ecosystems highlight the critical role of maintaining
 biodiversity components across multiple ecosystems. 
description: Between January and March 2010 (35 days), we manipulated
 predators and detritivores within bromeliads settled within experimental
 cages. Each cage consisted of a rectangular wire frame (0.50m × 0.60m)
 covered with a white fabric mesh that allowed moderate light to pass
 through, fixed to the top edge of a pot into which the experimental
 bromeliad was planted. An emergence trap, made of an inverted plastic
 bottle, was placed on top of each cage to capture adults of detritivores
 that emerged during the experiment. We randomly
 arranged these 48 bromeliads into 12 blocks of four bromeliads, with a
 minimum distance of 20 meters between blocks. We randomly assigned each
 block to the following treatments: (i) only detritivores, without
 predators (control treatment); (ii) detritivores + damselfly larva; (iii)
 detritivores + spider; (iv) detritivores + damselfly larva + spider. We
 used an additive design, in which the density of each predator species is
 held constant since this design, unlike a substitutive design, avoids
 confounding the absolute effect of interspecific interactions (in the
 predator co-occurrence treatment) with intraspecific interactions (Sih et
 al.1998; Romero & Srivastava, 2010). This allows us to assess
 predator impact regarding individual and multiple effects (i.e.,
 considering potential interspecific interactions between spider and
 damselfly larvae). Prior to the inclusion of the organisms, we added
 portions of approximately 15 previously dried and weighed leaves
 of <em>Eugenia uniflora</em> (Myrtaceae) (mean = 0.24g; SD ±
 0.002g) and of <em>Ocotea pulchella</em> (Lauraceae) (mean =
 0.57g; SD ± 0.009g) distributed equally among the bromeliad tanks. The
 litter of both plant species is commonly found inside the bromeliad tanks
 in the study area. We consider <em>E. uniflora</em> to be the
 higher quality litter for two reasons: (1) it has higher specific leaf
 area than <em>O. pulchella</em>, (97.77
 cm<sup>2</sup>.g<sup>-1</sup> ± 27.3, Migliorini
 et al., 2018; and 67.9
 cm<sup>2</sup>.g<sup>-1</sup> ± 5.0, Boerger
 & Wisniewski, 2003, respectively), often an indicator of higher
 palatability (Kurokawa et al., 2010; Schädler et al., 2003), which can
 also increase detrital decomposition rates (Migliorini et al., 2018); (2)
 it was fertilized with <sup>15</sup>N in order to trace
 nitrogen flux from detritus to bromeliads.  Once the
 litter was added, we added ten chironomids, five culicids, three
 limoniids, three scirtids, and two trichopterans in each experimental
 plant. The abundance of detritivorous groups in this experiment was based
 on natural abundance in bromeliads of similar size to the experimental
 bromeliads. After one day, we added a larva of the damselfly <em>L.
 andromache</em> (average body length = 11.3 mm ± 0.21 mm) and/or an
 adult female of the spider <em>C. demersa </em>according to
 predator treatments. We simulated the natural colonization of detritivores
 on the 18th day of the experiment by adding a further five chironomids,
 two culicids, a limonid, two scirtids, and a trichopteran. The abundances
 used in this simulated colonization were smaller than the initial quantity
 to avoid competition within each detritivore group in the phytotelmata.
 Thus, the inclusion of new individuals maintains the abundance of
 organisms that died or emerged during the experiments with other living
 organisms in each group of detritivores (Bernabe et al. 2018). We
 inspected the bottle traps daily for emerging adults, collecting and
 fixing the adults in 70% ethanol. At the end of the
 experiment, we removed each plant from the pot, counted the final number
 of bromeliad leaves (including new leaves), and clipped and collected
 three bromeliad leaves for isotopic analyses of
 <sup>15</sup>N. We then dissected the bromeliad, washing the
 leaves and contents on a white tray with water. We collected all the
 detritus, separating the dead leaves according to species and drying these
 in paper bags. Finally, we collected and recorded all of the
 macroinvertebrates. To verify whether the presence of the spider
 interferes with the growth of <em>L. andromache</em> larvae,
 we collected all damselfly exuviae, which indicates an increase in
 damselfly instar. We quantified the survival of each
 group of detritivores as the ratio between the abundance of survivors
 (i.e., remaining larvae and captured adults) and the total number of
 larvae used in the experiment. Thus, the survival percentage of
 detritivores considers the permanence of living organisms throughout the
 experiment, being an important approach to evaluate the role that
 detritivores play in the ecosystem. We estimated detritus decomposition as
 the percentage of original biomass lost of the two litter
 species, <em>O. pulchella</em> and <em>E.
 uniflora</em>. We measured the transfer of
 <sup>15</sup>N from <em>E. uniflora</em> debris to
 the bromeliad by quantifying the δ<sup>15</sup>N
 of <em>Q. arvensis</em> leaves at the end of the experiment
 (Appendix B). The vegetative growth of the bromeliads was approximated as
 the number of new leaves produced, that is, the difference between the
 initial marked leaves and final number of leaves.
description: # Trophic cascade within and across ecosystems: the role of anti-predatory
 defenses, predator type, and detritus quality
 The dataset is from a
 field experiment, in which we investigate how predators from adjacent
 ecosystems (aquatic and ecross ecosystem predators) affect functional
 groups of aquatic detritivores which differ in anti-predator defense, and
 indirectly detritus decomposition, nutrient cycling, and host plant
 growth. We used the aquatic invertebrate food webs in tank bromeliads as a
 model system to investigate these questions. We manipulated the presence
 of a strictly aquatic predator (damselfly larvae) and a predator with both
 terrestrial and aquatic habitats (spider), and examined effects on
 survival of prey (detritivores grouped by anti-predator defense), detrital
 decomposition (of two plant species differing in litter quality), nitrogen
 flux (15N) and host plant growth. Damselfly larvae and spiders each
 directly decreased survival of detritivores and caused multiple indirect
 negative effects on detritus decomposition, nutrient cycling, and host
 plant growth. However, when predators co-occurred, the spider caused a
 negative non-consumptive effect on the damselfly larva, diminishing the
 net direct and indirect top-down effects on the aquatic detritivore
 community and ecosystem functioning. Both detritivore traits and detritus
 quality modulated the strength and mechanism of these trophic cascades.
 Predator interference was mediated by undefended or partially defended
 detritivores as detritivores with anti-predatory defenses evaded
 consumption by damselfly larvae but not spiders. Predators and
 detritivores affected ecosystem decomposition and nutrient cycling only in
 the presence of high-quality detritus, as the low-quality detritus was
 consumed more by microbes than invertebrates. ## Description of the data
 and file structure The dataset is organized according to predictor and
 response variables obtained from the experiment. The abbreviation of each
 variable are: Trat: treatments Bloco: Block ZYG: Aquatic predator
 (Zygoptera) - presence/absence ARN: Cross ecosystem predator (spider) -
 presence/absence CHR: Chironomidae survival (percentage of survival) CLC:
 Culicidae survival (percentage of survival) LMN: Limoniidae survival
 (percentage of survival) SRT: Scirtidae survival (percentage of survival)
 TRC: Trichoptera survival (percentage of survival) Survtotal: Total
 detritivore survival (percentage of survival) Nleaves: New leaves
 production - plant growth BMTloss.perc: total detritus decomposition
 (percentage of detritus loss) BMOloss.perc: low quality detritus
 decomposition (percentage of detritus loss) BMEUloss.perc: high quality
 detritus decomposition (percentage of detritus loss) d15N: δ15N isotope
 det.prot: survival of protected detritivores (percentage of survival)
 det.p.prot: survival of partially protected detritivores (percentage of
 survival) det.unprot: survival of unprotected detritivores (percentage of
 survival) ## Sharing/Access information Data was derived from the
 following sources: * Original experiment, designed and conducted by the
 authors.