title: From endogenous to exogenous pattern formation: Invasive plant species changes the spatial distribution of a native ant.
abstract: Invasive species are a significant threat to global biodiversity, but our understanding of how invasive species impact native communities across space and time remains limited. Based on observations in an old field in Southeast Michigan spanning 35 years, our study documents significant impacts of habitat change, likely driven by the invasion of the shrub, Elaeagnus umbellata, on the nest distribution patterns and population demographics of a native ant species, Formica obscuripes. Landcover change in aerial photographs indicates that E. umbellata expanded aggressively, transforming a large proportion of the original open field into dense shrubland. By comparing the ant's landcover preferences before and after the invasion, we demonstrate that this species experienced a significant unfavorable change in its foraging areas. We also find that shrub landcover significantly moderates aggression between nests, suggesting nests are more related where there is more E. umbellata. This may represent a shift in reproductive strategy from queen flights, reported in the past, to asexual nest budding. Our results suggest that E. umbellata may affect the spatial distribution of F. obscuripes by shifting the drivers of nest pattern formation from an endogenous process (queen flights), which led to a uniform pattern, to a process that is both endogenous (nest budding) and exogenous (loss of preferred habitat), resulting in a significantly different clustered pattern. The number and sizes of F. obscuripes nests in our study site are projected to decrease in the next 40 years, although further study of this population's colony structures is needed to understand the extent of this decrease. Elaeagnus umbellata is a common invasive shrub, and similar impacts on native species might occur in its invasive range, or in areas with similar shrub invasions.
authors.affiliation: Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, NC, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Li
authors.affiliation: School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Yifan
authors.identifier: 0000-0002-8312-8071
authors.initials: Y
authors.lastname: He
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Susanna K
authors.initials: SK
authors.lastname: Campbell
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: A Shawn
authors.initials: AS
authors.lastname: Colborn
authors.affiliation: School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Eliot L
authors.initials: EL
authors.lastname: Jackson
authors.affiliation: School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Austin
authors.initials: A
authors.lastname: Martin
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Ivan V
authors.initials: IV
authors.lastname: Monagan
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Theresa Wei Ying
authors.initials: TWY
authors.lastname: Ong
authors.affiliation: School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Ivette
authors.initials: I
authors.lastname: Perfecto
mesh_terms: D000818:Animals; D001000:Ants; D017753:Ecosystem; D058865:Introduced Species; D008824:Michigan; D010944:Plants
keywords: 
  Elaeagnus umbellata
  ; 
  Formica obscuripes
  ; autumn olive; invasive species; landcover change; pattern formation; spatial distribution; thatching ant