From species to communities: the signature of recreational use on a tropical river ecosystem

Abstract

Disturbance can impact natural communities in multiple ways. However, there has been a tendency to focus on single indicators of change when examining the effects of disturbance. This is problematic as classical diversity measures, such as Shannon and Simpson indices, do not always detect the effects of disturbance. Here, we instead take a multilevel, hierarchical approach, looking for signatures of disturbance in the capacity and diversity of the community, and also in allocation and demography at the population level. Using recreational use as an example of disturbance, and the freshwater streams of Trinidad as a model ecosystem, we repeatedly sampled the fish communities and physical parameters of eight pairs of recreational and nonrecreational sites every 3 months over a 28‐month period. We also chose the Trinidadian guppy (Poecilia reticulata) as the subject of our population‐level analyses. Regression tree analysis, together with analysis of deviance, revealed that community capacity and community species richness were greater at sites with higher levels of recreational use. Interestingly, measures of community diversity that took into account the proportional abundance of each species were not significantly associated with recreational use. Neither did we find any direct association between recreational use and proportion of guppy biomass in the community. However, population‐level differences were detected in the guppy: Sex ratio was significantly more female‐biased at more disturbed sites. Our findings emphasize the importance of considering multiple levels when asking how disturbance impacts a community. We advocate the use of a multilevel approach when monitoring the effects of disturbance, and highlight gaps in our knowledge when it comes to interpreting these effects.

Predation pressure shapes brain anatomy in the wild

“…; Botham et al 2006;Deacon et al 2015;Endler 1980;Rodd and Reznick 1991;Seghers 1974). We found several other fish species at those sites, but they are not believed to consume adult guppies (personal communication Rajindra Mahabir).…”

“…The data on predation pressure was originally collected for a study on temporal patterns of biodiversity and the impact of human recreational use of rivers on community ecology in Trinidad's Northern Range; see Deacon et al (2015) for detailed sampling protocol. In brief, 16 sites (50 m stretches), closely matched in terms of stream order, flow rate, size, and isolation were sampled over a 5-year period, at 3-monthly intervals.…”

“…The logic behind this is that a higher biomass of predators needs more food to support its existence (Endler 1978). As the sites are of similar size and topography (Deacon et al 2015), predator biomass should determine predator pressure. We used only animals [1 g in those calculations, as smaller individuals are unlikely to consume adult guppies.…”

“…Here we take advantage of the recent and most complete investigation of Trinidadian river biodiversity to date (Deacon et al 2015) to investigate the effect of predation on brain anatomy in wild populations. We do this by relating data on predator community composition to brain anatomy of guppies from 16 wild populations that are closely matched in stream characteristics (Deacon et al 2015).…”

“…We do this by relating data on predator community composition to brain anatomy of guppies from 16 wild populations that are closely matched in stream characteristics (Deacon et al 2015). Because a larger brain confers a cognitive advantage and so improves predator-related performance (Kotrschal et al 2015a;van der Bijl et al 2015), we predict that increased predation pressure selects for larger brains.…”