Effects of ecological niche construction on life history and mating patterns

Animals often modify the environments in which they live. They may build structures to help them raise offspring, take shelter from predators, or escape harsh abiotic conditions. They may burrow into the ground as they seek food, or rearrange resources as they establish and maintain territories. Even their mere presence in a habitat can produce physical and chemical changes to the landscape that can have a myriad of knock-on consequences for all the organisms sharing the same space. The idea that animals exert effects on their surroundings in ways that can then feed back on them and even affect their evolutionary selection pressures is encapsulated by the concept of “ecological niche construction”. In theory, ecological niche construction can have a staggeringly broad range of effects, but specifically measuring these effects in the wild is notoriously difficult. 

In this project, I take advantage of a unique natural experiment taking place in Lake Tanganyika, East Africa, to measure consequences of ecological niche construction. Within Lake Tanganyika, there are habitats called ‘shell beds’, which are regions of the sandy lake floor covered by vast accumulations of empty snail shells. These habitats are home to an assemblage of cichlid fish species that are specially adapted to use these shells as shelters – which they dig up from the lake floor. In some regions of the shell bed, the fish are able to use the sand that they scoop up to build sand walls between themselves and their neighbours, which produces a cratered, almost lunar, landscape on the lake floor with clusters of shells denoting their territories. However, in other regions of the shell bed (very nearby) there is no sand, and so the fish cannot construct sand walls and the shells do not get rearranged into clusters. This presents an excellent opportunity to compare and contrast the populations of fish living under these two habitat types that differ primarily in the fish’s own ability to niche construct (i.e., to build sand walls). 

This fieldwork involves a combination of genetic parentage analyses and morphometric measurements to assess how the fish’s own niche construction behaviours can produce differences in mating patterns, social structure, and life history.