Density-Dependent Effects of an Early Season Insect Herbivore on a Later Developing Insect Herbivore

Abstract

Although most North American grasshopper species overwinter as eggs, some species hatch in late summer, overwinter as nymphs, and become adults in late spring. These species periodically reach outbreak densities, but it is unknown if they impact the population dynamics of later developing egg-overwintering grasshopper species. Two experiments were conducted in a northern mixed-grass prairie to examine the effects of herbivory by nymph-overwintering grasshoppers on survival of an egg-overwintering grasshopper, Ageneotettix deorum. When very high densities of nymph-overwintering grasshoppers reduced grass biomass by 80%, survival of A. deorum nymphs was significantly reduced. There was no effect of early season herbivory at a lower density of 16/m(2) on survival of A. deorum nymphs. The effects of early season herbivory appear consistent with exploitative competition. Although a strong reduction in peak grass biomass caused by early season herbivory negatively affected late season grass-feeding grasshopper densities, additional research is needed to examine the potential importance of early summer herbivory on population dynamics of later developing grasshoppers.

Seed wasp invasions promoted by unregulated seed trade affect vegetal and animal biodiversity

“…Thus, differences in the timing of adult emergence might confer a competitive advantage. The increased fitness of seasonallyearlier adapted individuals in competitive interactions has been suggested several times as an argument for the invasion success of exotic insects through a pre-emption of resources that creates size (developmental) or numerical advantages (Branson 2010;Kajita & Evans 2010;Rhainds et al 2010;Louda et al 2011). Nevertheless, the seed chalcid strategies varied with species and the late species did not appear to be systematically disadvantaged.…”

Exotic herbivores on a shared native host: tissue quality after individual, simultaneous, and sequential attack

“…Because of this, even when the initial attacker is no longer present, phenotypic changes in host plants can indirectly impact future enemies by increasing resistance (Inbar et al 1999;Soler et al 2007) or by increasing susceptibility to a second attacker (Thaler et al 2002;Zarate et al 2007). These plant-mediated changes can alter herbivore population dynamics through resource competition (Branson 2010), the attraction of natural enemies (De Boer et al 2008), and/or induced changes in leaf chemistry (Poelman et al 2008).…”

Ecosystem carbon exchange in response to locust outbreaks in a temperate steppe

“…By contrast, Dyer et al (1993) have found that low-level herbivory under non-outbreak conditions could increase plant production, whereas extremely high-intensity herbivory under outbreak conditions results in substantial productivity reduction. At outbreak density, grasshopper herbivory could reduce approximately 70-95 % of the aboveground biomass in short-and mixed-grass prairies (Burleson and Hewitt 1982;Chase 1996;Thompson et al 1996;Carson and Root 2000;Branson 2010;Branson and Haferkamp 2014). Therefore, clipping 80 % of aboveground biomass in this study could well have simulated biomass losses caused by locust feeding under outbreak conditions.…”

“…On the one hand, insects that feed on plant aboveground tissues can substantially suppress plant growth (Hoogesteger and Karlsson 1992;Jardon et al 1994;Coupe and Cahill 2003;Esper et al 2007;Cobb 2010) and biomass (Schowalter et al 1986;Brown 1994;Chase 1996; Thompson et al 1996;Carson and Root 2000;Branson 2010;Branson and Haferkamp 2014) under outbreak conditions, consequently leading to significant declines in ecosystem function. For instance, the depressed plant growth and productivity caused by the outbreaks of mountain pine beetle can suppress forest ecosystem carbon (C) uptake in North America (Kurz et al 2008a, b;Brown et al 2010;Clark et al 2010;Dymond et al 2010;Stinson et al 2011).…”