Wood ants on the edge: how do the characteristics of linear edges affect the population dynamics of an edge specialist?

Landscape structure may facilitate or inhibit the dispersal of species by presenting barriers or opportunities. Slow dispersing edge specialists are likely to be most affected by local topography and land management practices because they require two different adjacent habitats within their limited dispersal range. The northern hairy wood ant, Formica lugubris, requires adjacent forest and open habitats to access aphid honeydew, invertebrate prey, and direct sunlight for thermoregulation. In plantation forest, canopy gaps that provide this combination are often linear and anthropogenic, such as paths, firebreaks, and roads (collectively termed ‘rides’), and their orientation determines shade distribution. Using population data spanning 10 years, we ask how properties of rides, such as bearing and width, affect the distribution and dispersal of wood ant populations in the North York Moors. Regardless of orientation, nests were more abundant on the north side of rides, where they receive more sunlight, and nests were generally larger on narrower rides. Furthermore, we found that F. lugubris dispersed approximately 3 times quicker along rides that were oriented north-south or east-west compared to NE-SW or NW-SE. Because wood ants can suppress defoliating pests, these findings have potential forest management implications and may apply to other forest dwelling edge specialists.