Staying around the mound is sound

Posted on September 21, 2011

The largest family of fishes in the world, the Cyprinidae (minnows and carps) contains over 2400 species.   In North America, cyprinids account for almost a third of all fish species, but around 20% of these are endangered due to the impacts of habitat loss, pollution, overexploitation and invasions of exotic species.  However, there’s growing evidence that the protective spawning behaviour and parental care provided by many minnow species is an important source of resilience in the face of environmental threats.   Around 40% of North American minnows protect their eggs and young, rather than just broadcasting and abandoning their eggs over an unprepared substrate.  Protective behaviours include crevice-spawning, pit-building, pit/ridge-building, saucer-building, mound-building, egg-clumping and egg-clustering.  Interestingly, the nests constructed by these species are also used as spawning sites by minnows of other species, which benefit from the parental care provided by the host, and in return, the increase in the number of deposited eggs serves to dilute predation pressure on the host’s  brood.  A study in the New River, Virginia, U.S.A. suggests that cyprinids that build and spawn on mounds of gravel act as keystone species that allow other fish species to invade headwater streams and persist there.  By comparing the results of contemporary  surveys with those carried out in the same streams in 1938-1941, the authors concluded that 11 fish species had become established in the intervening period.  Of 14 traits related to life history, reproductive strategy, feeding mode, habitat use and taxonomy, the tendency to  associate with mound-building species was the most important predictor of persistence at the sampled sites.  Additional support for this relationship was found in the fact that three species – all natives unassociated with mound-building – were lost from the system over the same period.  This study provides a good example of how the behaviour patterns of particular species can have wide-ranging impacts on the structure of freshwater fish communities.

Reference:  Hitt, N.P. & Roberts, J.H.  2011.  Hierarchical spatial structure of stream fish colonization and extinction.  Oikos 000: 001–011, 2011  doi: 10.1111/j.1600-0706.2011.19482.x  Published online 9 May 2011.