Untangling the complex food webs of tropical rainforest streams

Author(s)

Saito, Victor S. ; Kratina, Pavel ; Barbosa, Gedimar ; Ferreira, Fabio Cop ; Leal, Jean Barbosa ; Zemelka, Gabriela ; Sarmento, Hugo ; Perkins, Daniel M.

• Document type: Journal article
• Source: Journal of Animal Ecology; v. 93, n. 8, p. 14-pg., 2024-06-07.

Abstract

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems. Here, we first characterised a tropical stream meta-food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population-level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka-Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability. The model resulted in a stable meta-food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta-food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non-specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale. Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size-dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human-impacted landscapes. As teias alimentares representam um emaranhado de intera & ccedil;& otilde;es tr & oacute;ficas associadas ao funcionamento de um ecossistema. Compreender os mecanismos que proporcionam estabilidade a estas teias alimentares & eacute;, portanto, vital para os esfor & ccedil;os de conserva & ccedil;& atilde;o e gest & atilde;o dos sistemas naturais. Aqui, primeiro caracterizamos uma meta teia alimentar de riachos tropicais e cinco teias alimentares individuais usando uma abordagem hier & aacute;rquica Bayesiana unificando tr & ecirc;s fontes de informa & ccedil;& atilde;o (an & aacute;lise de conte & uacute;do estomacal, compila & ccedil;& atilde;o de literatura, dados de is & oacute;topos est & aacute;veis). Com dados sobre biomassa em n & iacute;vel populacional e massa corporal medida individualmente, aplicamos um modelo bioenerg & eacute;tico e avaliamos a estabilidade da cadeia alimentar usando um sistema de equa & ccedil;& otilde;es Lotka-Volterra. Em seguida, avaliamos a resili & ecirc;ncia do sistema & agrave;s extin & ccedil;& otilde;es de esp & eacute;cies individuais usando simula & ccedil;& otilde;es e investigamos os padr & otilde;es de rede associados a sistemas com maior estabilidade. O modelo resultou em uma meta teia alimentar est & aacute;vel com 307 liga & ccedil;& otilde;es entre os 61 componentes. Na escala regional, 70% do fluxo total de energia ocorreu atrav & eacute;s de um conjunto de dez taxa com grande varia & ccedil;& atilde;o nas massas corporais. Os restantes 30% do fluxo total de energia dependiam de 47 taxa diferentes, apoiando uma depend & ecirc;ncia significativa de uma comunidade diversificada. A meta teia alimentar foi est & aacute;vel contra extin & ccedil;& otilde;es de esp & eacute;cies individuais, com uma maior resili & ecirc;ncia em teias alimentares que abrigam esp & eacute;cies de peixes on & iacute;voros capazes de conectar m & uacute;ltiplos compartimentos da teia alimentar atrav & eacute;s de intera & ccedil;& otilde;es fracas e n & atilde;o especializadas. Al & eacute;m disso, estas esp & eacute;cies de peixes contribu & iacute;ram amplamente para a varia & ccedil;& atilde;o espacial entre as cadeias alimentares individuais, sugerindo que estas esp & eacute;cies poderiam operar como predadores m & oacute;veis conectando diferentes riachos e estabilizando a variabilidade & agrave; escala regional. Nossos resultados descrevem dois mecanismos principais de estabilidade da cadeia alimentar operando em riachos tropicais: (i) a diversidade de esp & eacute;cies e massas corporais que protegem contra dist & uacute;rbios aleat & oacute;rios e dependentes do tamanho (ii) alta diversidade regional e fracas intera & ccedil;& otilde;es on & iacute;voras de predadores que protegem contra a varia & ccedil;& atilde;o estoc & aacute;stica local na composi & ccedil;& atilde;o de esp & eacute;cies. Estes mecanismos dependem de uma elevada biodiversidade local e regional em riachos tropicais, que s & atilde;o conhecidos por serem fortemente afetados pelos impactos humanos. Portanto, um desafio urgente & eacute; compreender como a cont & iacute;nua perda sistem & aacute;tica de diversidade p & otilde;e em risco a estabilidade das teias alimentares em paisagens impactadas pelo homem. We described a tropical stream food web and estimated its stability. We found stable systems where species contributed to ecosystem functioning in two ways: A diverse set of small taxa contributes to total energy flow, while large omnivorous taxa stabilise the system by connecting compartments at local and regional scales.image (AU)

• FAPESP's process: 20/07522-6 - Testing trophic stochasticity in tropical streams through allometric relationships
• Grantee: Jean Barbosa Leal
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 19/05464-1 - Comparing the structure and dynamics of tropical and temperate freshwater communities
• Grantee: Hugo Miguel Preto de Morais Sarmento
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• FAPESP's process: 22/01452-1 - Understanding the role of stochasticity in metacommunity assembly under global changes
• Grantee: Victor Satoru Saito
• Support Opportunities: Regular Research Grants