Aggregated Distribution as an Explanation for the Paradox of Plankton and Collective Animal Behavior

Abstract

This work analyzes the evolutionary consequences of different aggregation levels of species distribution with an Evolutionary Cellular Automaton (ECA). We have found that in habitats with the same carrying capacity, aggregated distributions preserve smaller populations than do uniform distributions, i.e., they are less efficient. Nonetheless, we have also found that aggregated distributions, among other factors, can help the evolutionary stability of some biological interactions, such as predator–prey interactions, despite their granting less individual fitness. Besides, the competitive exclusion principle does not usually stand in populations with aggregated distribution. We have applied ECA to study the effects of aggregated distribution in two notorious cases: in the so-called paradox of the plankton and in gregarious animals. In doing so, we intend to ratify long-established ecological knowledge explaining these phenomena from a new perspective. In the first case, due to aggregate distribution, large aggregations of digital organisms mimicking very abundant planktonic species, leave large patches or oceanic areas free for other less competitive organisms, which mimic rare species, to prosper. In this case, we can see how effects, such as ecological drift and the small portion, act simultaneously. In the second case of aggregation, the aggregate distribution of gregarious animals could be explained under specialized predator–prey interactions and interdemic competition. Thus, digital organisms that imitate predators reduce the competitive capacity of their prey, destabilizing their competitiveness against other species. The specialized predator also goes extinct if the prey goes extinct by natural selection. Predators that have an aggregate distribution compensate the prey and thus avoid exclusion. This way there are more predator-free patches in which the prey can prosper. However, by granting greater colonization capacity to its prey, the predator loses competitiveness. Therefore, it is a multilevel selection event in which group adaptation grows to the detriment of the predator as an individual.

Distinctive chemotactic responses of three marine herbivore protists to DMSP and related compounds

“…Our study also demonstrates that chemotaxis favours protist aggregation on or around a DMSP source. In marine ecology, aggregation brings a trade-off of advantages and risks that is hard to resolve: contradictory results exist on the effects of aggregation on the probability of feeding and being predated [ 73 , 74 ]. For heterotrophic dinoflagellates, enhanced feeding by aggregation on marine snow has been documented [ 75 ], and marine snow particles can be DMSP-rich [ 27 ]; therefore, chemotaxis-driven aggregation on marine snow may be a beneficial collective behaviour for micrograzers.…”