Please join us for the seminar "Invasion! A Niche Perspective," presented by Robert Warren, associate professor of biology, on Monday, March 6, from 4:00 to 5:15 p.m. in Bulger Communication Center East 2. All students, staff, and faculty are welcome. This event is sponsored by the Biology Department, the Great Lakes Center, and the Great Lakes ecosystem science program.
Seminar Abstract
Species coexist through a balance of equalizing (similar fitness abilities) and stabilizing (at least somewhat different niche requirements) mechanisms. These forces maintain coexistence if intraspecific competition limits a species more than interspecific competition (Chesson 2000). That is, a species likely competes more with itself than with another species for the same niche requirements. Introduced species often destabilize coexistence and reduce or eliminate other species. Species invasion depends on a fitness advantage or a distinct niche requirement. Most invasion biology theory assumes both: invasive species are better competitors and occupy unique niches. Native ant diversity and abundance generally plummets in the presence of invasive ants. Whether invasive ant dominance is primarily caused by antagonistic interactions in which the invading ant suppresses the natives or by habitat alteration in which the invasive ants exploit novel conditions that do not support natives remains an unsettled question. A third possibility is that invasive ants violate the key assumption of coexistence theory: intraspecific competition > interspecific competition.
A common feature among highly invasive ants is the formation of supercolonies in which multiple ant colonies share queens and workers. We tested the competing hypotheses that strong fitness differences and/or niche differences would explain the dominance of an invasive ant (Myrmica rubra) at Tifft Nature Preserve in Buffalo. We used monthly M. rubra censuses from 1994 and 2015, transect surveys, abiotic and biotic habitat data, M. rubra foraging, lipid content and biomass assessments, potential invasive plant facilitation, isotope analysis, and aggression bioassays to test these hypotheses. We found little evidence of competitive advantage or strong niche differentiation. Instead, we found exceedingly low intraspecific competition among M. rubra colonies relative to the putative dominant native ant, Aphaenogaster rudis, which competed with itself as much as with M. rubra. Our evidence suggests that M. rubra colonies lack intraspecific limitation and exceed carrying capacity before seasons end, resulting in the elimination of co-occurring native species as well as a crash in M. rubra populations. These findings suggest an unexplored mechanism of species invasion: friendly release. That is, freed up from the costs and limitations of territoriality, invasive species may out-compete native species by not competing with themselves. This hypothesis may generalize well to other invaders, such as plants, and it places invasion biology within the context of ecological theory.
