What are the impacts of introduced piscivores on native food webs?
Another potential consequence of biological invasions is the alteration of native food webs. However, quantifying the impacts of introduced species on native food webs in the field can be challenging, given the large number of species and complex interactions involved. To address this challenge, I use a combination of approaches, including detailed field-based observations, stomach content analysis of both contemporary and historical (museum) specimens, and stable isotope analysis (SIA). SIA offers great promise for disentangling complex trophic relationships and tracking the flow of energy and nutrients in natural ecosystems, but has yet to be widely applied to tropical food webs.
I first explored these questions in Lake Victoria (East Africa), where the introduction of the predatory Nile perch, Lates niloticus, in the 1960s led to dramatic community-level changes, including the extirpation of hundreds of endemic haplochromine cichlids. I hypothesized that such losses of entire functional guilds would present ecological opportunities to resilient species that persisted through the introduction. To test this, I used museum specimens from the 1960s to compare the trophic ecology of a commercially-important, resilient endemic species (Rastrineobola argentea) before versus after the introduction of the Nile perch. I found that R. argentea incorporated novel prey into their diet, leading to a broadening of their trophic niche, potentially signaling competitive release following the extirpation of competitors.
I first explored these questions in Lake Victoria (East Africa), where the introduction of the predatory Nile perch, Lates niloticus, in the 1960s led to dramatic community-level changes, including the extirpation of hundreds of endemic haplochromine cichlids. I hypothesized that such losses of entire functional guilds would present ecological opportunities to resilient species that persisted through the introduction. To test this, I used museum specimens from the 1960s to compare the trophic ecology of a commercially-important, resilient endemic species (Rastrineobola argentea) before versus after the introduction of the Nile perch. I found that R. argentea incorporated novel prey into their diet, leading to a broadening of their trophic niche, potentially signaling competitive release following the extirpation of competitors.
R. argentea had a broader dietary niche after the Nile perch introduction (Sharpe and Chapman 2014)
In Lake Gatun, we are using a combination of stomach contents analysis and SIA to examine the food-web consequences of the introduction of the predatory peacock bass. In collaboration with Marisol Valverde, we have examined trophic interactions between this novel predator and Gatun’s previously-dominant native predator, the dogfish Hoplias microlepis. We are now in the process of expanding this isotopic analysis to the entire lacustrine food web to elucidate trophic pathways between multiple introduced and native species in this very dynamic community.
Publications related to this work:
- Sharpe, D. M. T., De León, L. F., González, R. and Torchin, M. E. 2017. Tropical fish community does not recover 45 years after predator introduction. Ecology, 98: 412–424. doi:10.1002/ecy.1648
- Valverde, M., D.M.T Sharpe, M.E. Torchin, D.G. Buck, and L.J. Chapman. Trophic shifts in a native predator following the introduction of a top predator in a tropical lake (In Review, Biological Invasions)
