Vol. 7 - What happens to food webs after environmental catastrophes?
Studying fish communities post-dam failure reveals trophic changes and highlights the fragility of food webs in disrupted environments.
Over the past few years, with the help of truly fantastic grad students, I got more invested in the idea of using food web structure to get clues about the state of the environment in which these food webs operate.
And so, today's paper caught my eye because it is a really thorough chronicle of the recovery of the fish communities following the Doce River basin dam failure, which took place in 2015.
de Carvalho, D.R., Ferreira, F.F., Dergam, J.A., Moreira, M.Z. & Pompeu, P.S. (2024). Food web structure of fish communities of Doce River, 5 years after the Fundão dam failure. Environ. Monit. Assess., 196.
When the Fundão dam failed, millions of cubic meters of mining tailings spread over hundreds of kilometres, until reaching the Atlantic Ocean. Close to a decade later, the authors sampled several locations in the same watershed, including seven directly downstream of the dam, and three controls in locations upstream of the tailing mud flow. These later locations are proxies for the variation that we could expect in this region without the influence of the dam failure and subsequent position.
At the locations closer to the rupture, the trophic structure of the fish communities was the most simplified. This simplification was expressed as a loss of diversity, but also as more homogeneous feeding strategies. The trophic complexity did not increase until the locations further away from the rupture.
One of the neatest results in the paper, I think, is the relationship between the distance to the rupture and the trophic niche breadth. Fishes further away from the rupture were three to four times more generalists than fishes closest to the rupture. This is a substantial difference in terms of complementarity, albeit one that is not unexpected for stream-dwelling communities.
Taken together, these results point to an interesting signature of how food webs can react to a massive environmental disruption: trophic simplification, loss of richness, and more diet specificity. What is intriguing is that these conditions are the opposite of homogenization: they result in food webs that are fragile because they are perilously close to unravelling.
Tracking the empirical differences in food webs at different distances from a perturbation is a great way to develop insights about how we can tailor indicators (based on food web structure) to track recovery (or, more broadly, status). Food web ecology has generated an immense corpus of measures of structure; and yet, these measures are not always indicators, in that we do not have a high confidence that they measure aspects of food webs that are relevant for management or monitoring. In order for food web monitoring to become mainstream, there is an interesting work of translation ahead of us, to pick (and evaluate) which measures can guide actions.
With all that said, stay tuned for Vol. 8 next week, where I will Have Opinions about outreach (and why it is over-rated).