Eating their way to the top? Mechanisms underlying the success of invasive insect generalist predators

Abstract

Insect generalist predators have been introduced outside of their native range intentionally to improve biological control, or accidentally during commerce, and can subsequently become invasive. Invasive insect generalist predators (IIGP) have widespread impacts on invaded communities because they consume both herbivores and other predators. Also, they often reach higher densities than and displace similar native species. Reflecting the complexity of their ecological roles, a wide variety of mechanisms might contribute to invasive success by IIGP. These species often drive resources to lower levels than do natives, leading to intense resource competition and sometimes competitive exclusion of other predators. The broader range of resources used by many IIGP can heighten their competitive advantage, particularly when IIGP exploit modified habitats. In either case, IIGP improve herbivore suppression by depressing prey densities below preinvasion levels. Coexistence among native and invasive generalists is fostered when species differ substantially in their niche requirements. In this case, a larger proportion of the total prey population is subject to attack post-than pre-invasion, which strengthens prey suppression. On the other hand, some IIGP feed heavily on other predators, at times leading to a weakening of prey suppression. Future research should continue to explore the roles of competition and niche partitioning on larger spatial scales, and in both the native and invasive ranges of IIGP. Additionally, combining data from empirical studies with theory might be an effective way to predict the spread and community impacts of IIGP invasions.

The hitchhiker’s guide to alien ant invasions

“…Depending on local environmental settings and management practices, however, the addition of new predators into natural and managed ecosystems may further reduce herbivore populations or it may reduce overall benefit to primary producers by increasing competition and intraguild predation (e.g. Eubanks 2001;Snyder and Evans 2006;Bruno and Cardinale 2008;Crowder and Snyder 2010). The historic and successful intentional release of Monomorium pharaonis (Linnaeus, 1758) against bed bugs (Cimex lectularius Linnaeus, 1758) (Hemiptera: Cimicidae) in British army barracks in Gibraltar can be mentioned as a curiosity here (Jameson 1932).…”

Eating the competition speeds up invasions

“…This work yields two important general predictions: (i) invasion success of species feeding at multiple trophic levels should be higher, and (ii) their invasion speeds faster, than for introduced species feeding only on lower trophic levels. Prediction (i) is supported by recent theoretical and empirical studies [15,16]. Anecdotal evidence exists for prediction (ii); for example, estimated spread rates for the harlequin ladybird in Britain (58 -144.5 km yr 21 [7]) are an order of magnitude higher than those of another notorious invader, the grey squirrel (7.66 km yr 21 [12]).…”

Comparison of Body Size and Wing Type in Beetles Found on Green Roofs and Adjacent Ground Sites in Portland, Oregon

“…Beetles have caused many issues regarding invasion, by outcompeting with native species for resources and destroying local flora (Crowder and Snyder 2010). Some prominent examples include the Colorado potato beetle and the Asian long-horned beetle.…”

“…In particular, breeding patterns and diet are traits that would be interesting to compare to wings and body size to better create a profile of what types of beetles are successful on green roofs. In one study on feeding habits, the researchers found that the type of predation, generalist or specific, plays a role in successful colonization (Crowder and Snyder 2010). Dispersal is also affected by season and stability of the habitat, which are factors that may differ between green roofs and ground environments (Boivin & Hance 2003).…”

“…Wing size, body size, breeding location, diet, and other traits all play a role in an insect's success, especially in a new environment (Shibuya et al 2014, Yamashita et al 2006, Ogai and Kenta 2015. For example, insects that are generalist predators tend to be more successful at entering new environments because they are able to thrive on whatever food is most available (Crowder and Snyder 2010).…”