“Uniform Prey Results in a World Domination by Spider-Eating Spiders,” Reports Nebraska Today

A recent study by the University of Nebraska-Lincoln revealed that a limited menu of prey can cause multiple species of wolf spiders to dine on each other or even cannibalize themselves. Ecologists have previously believed that predators with similar diets split their food sources to facilitate competition, leaving enough prey for everyone. However, when each other’s prey lacked diversity, eight-legged predators would feed on each other instead.

Mating may help maintain ecological equilibrium, but the decline in prey species is bad news for weaker predators, leading to direct competition from stronger opponents. However, predators that occasionally succeed in killing or eating their more competitive peers may benefit from an “equalization mechanism” that reduces the population of better predators, resulting in less competition.

The team collected specimens of eight wolf spider species and their potential prey using a customized vacuum cleaner. The spiders had an almost identical diet which was unexpected, given that they were found in slightly different places, looked different, and behaved differently.

To differentiate spider DNA, the team used unique DNA sequence barcodes for each type of prey consumed by the spiders. However, analyzing nitrogen isotopes in every wolf spider tissue sample collected showed the team that they were more likely to be eating spiders than other prey. The spider’s ranking far exceeded the team’s expectations, indicating that this level of complexity and predation was crucial in determining how the entire system worked.

The team found that only prey diversity, or lack thereof, was associated with wolf spiders attacking their own prey, as opposed to variables such as predator sex and size, environmental characteristics, and prey number and diversity. Foraging in the field is much different from foraging in petri dishes in the lab, as the wild has many other factors at play, such as the fear of being eaten by predators, finding mates, and parasites.

The study’s authors believe that these findings indicate a much more complex and recursive food web than previously thought, with everyone eating everyone and compounding in itself. The implications of how food webs are structured are unlike anything that was previously imagined, and while the research was conducted using wolf spiders, the same can be said for any system.

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