Environmental and hydrological drivers of ectoparasite-fish host interactions in the Southern Amazon: insights from ecological networks and interaction beta diversity.

Abstract

The Teles Pires River, a major tributary of the Tapajós River in the Southern Amazon, has been increasingly affected by anthropogenic activities such as agribusiness, mining, and the construction of hydroelectric dams. These disturbances significantly alter the local ecological dynamics, which remain poorly understood particularly with regard to fish–parasite interactions. Given the scarcity of studies and the ongoing environmental degradation, understanding how environmental and hydrological factors shape these interactions is essential for guiding conservation and management strategies. In the first chapter, we analyzed ectoparasite–fish host interactions across three aquatic environment types (main river channel, floodplain lakes, and tributary streams) during two distinct hydrological periods (rainy and dry seasons). Ecological network metrics (H2’ specialization index and Shannon diversity of interactions H’) and beta diversity indices both taxonomic (βtax) and interaction-based (βst, βrw, βwn)—were used to assess how environmental conditions and seasonal hydrology influence host–parasite network structure. Parasite species specialization was also estimated using the d’ index. In the second chapter, we investigated the parasitic dynamics of candirus (Paracanthopoma parva) by applying Generalized Linear Models (GLMs) to test the effects of host characteristics (standard length, sex, and trophic category), as well as environmental variables (hydrological period and sampling time), on the occurrence and intensity of parasitism. Results showed that host size, rainy season, and nocturnal sampling significantly increased the likelihood of interaction, while parasitism intensity was higher in females. These findings emphasize the importance of incorporating both environmental and biological factors when analyzing parasitic interactions, and demonstrate that ectoparasites particularly in dynamic Neotropical environments like the Amazon are effective models for understanding ecological interactions.