Effects of Consumer Interactions on Benthic Resources and Ecosystem Processes in a Neotropical Stream

Abstract

The effect of consumers on their resources has been demonstrated in many systems but is often confounded by trophic interactions with other consumers. Consumers may also have behavioral and life history adaptations to each other and to co-occurring predators that may additionally modulate their particular roles in ecosystems. We experimentally excluded large consumers from tile periphyton, leaves and natural benthic substrata using submerged electrified frames in three stream reaches with overlapping consumer assemblages in Trinidad, West Indies. Concurrently, we assessed visits to (non-electrified) control frames by the three most common large consumers–primarily insectivorous killifish (Rivulus hartii), omnivorous guppies (Poecilia reticulata) and omnivorous crabs (Eudaniela garmani). Consumers caused the greatest decrease in final chlorophyll a biomass and accrual rates the most in the downstream reach containing all three focal consumers in the presence of fish predators. Consumers also caused the greatest increase in leaf decay rates in the upstream reach containing only killifish and crabs. In the downstream reach where guppies co-occur with predators, we found significantly lower benthic invertebrate biomass in control relative to exclosure treatments than the midstream reach where guppies occur in the absence of predators. These data suggest that differences in guppy foraging, potentially driven by differences in their life history phenotype, may affect ecosystem structure and processes as much as their presence or absence and that interactions among consumers may further mediate their effects in these stream ecosystems.

Landscape patterns in top‐down control of decomposition: omnivory disrupts a tropical detrital‐based trophic cascade

“…A study by Marshall et al. (), in the same focal study stream as our current study, found that killifish were active both day and night (cathemerally active), whereas guppies were diurnal and crabs nocturnal. Thus, we deployed four exclosure treatments: 24‐h total exclusion, 12‐h daytime exclusion, 12‐h nighttime exclusion, and a 24‐h access control treatment.…”

The evolution of coexistence: Reciprocal adaptation promotes the assembly of a simple community

“…; Marshall et al. ). This feedback loop between ecological and evolutionary dynamics, often denoted “eco‐evo feedbacks” (Kokko and López‐Sepulcre ; Schoener ; Travis et al.…”

“…) and have shown that the mesocosms are reasonable facsimiles of natural streams (Marshall et al. ).…”

Local adaptation of fish consumers alters primary production through changes in algal community composition and diversity

“…The fence charger produced a 1 J shock every two seconds (for details, see Pringle and Blake , Connelly et al ). This power range was large enough to keep guppies from entering the quadrats, but was not powerful enough to affect the movement of smaller invertebrates or primary producers (Bassar et al , Marshall et al ). Each mesocosm also contained an identical but non‐electrified quadrat.…”

“…Guppies are the dominant consumers of algae in LP streams. Exclosure experiments in natural streams have shown that LP guppies reduce the standing crop of algal biomass (measured as mass of chlorophyll‐a) more than HP guppies (Marshall et al ). HP guppies are less herbivorous than LP guppies and consume more invertebrates in both experiments in mesocosms and in natural streams (Bassar et al , , Zandonà et al ).…”