Estimating the relative roles of top-down and bottom-up forces on insect herbivore populations: A classic study revisited

Abstract

Although most ecologists agree that both top-down and bottom-up forces (predation and resource limitation, respectively) act in concert to inf luence populations of herbivores, it has proven difficult to estimate the relative contributions of such forces in terrestrial systems. Using a combination of time-series analysis of population counts recorded over 16 years and experimental data, we present the first estimates of the relative roles of top-down and bottom-up forces on the population dynamics of two terrestrial insect herbivores on the English oak (Quercus robur). Data suggest that temporal variation in winter moth, Operophtera brumata, density is dominated by time-lagged effects of pupal predators. By comparison, spatial variation in O. brumata density is dominated by host-plant quality. Overall, top-down forces explain 34.2% of population variance, bottom-up forces explain 17.2% of population variance, and 48.6% remains unexplained. In contrast, populations of the green oak tortrix, Tortrix viridana, appear dominated by bottom-up forces. Resource limitation, expressed as intraspecific competition among larvae for oak leaves, explains 29.4% of population variance. Host quality effects explain an additional 5.7% of population variance. We detected no major top-down effects on T. viridana populations. An unknown factor causing a linear decline in T. viridana populations over the 16-year study period accounts for most of the remaining unexplained variance. We discuss the observed differences between the insect species and the utility of time-series analysis as a tool in assessing the relative importance of top-down and bottom-up forces on herbivore populations.

Os tricomas de Capsicum spp. interferem nos aspectos biológicos do ácaro-branco, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)?

“…A longo prazo, podem ter consequências sobre a dinâmica populacional desses organismos, já que atuam sobre seu desenvolvimento, sobrevivência e reprodução. O papel que plantas e inimigos naturais desempenham na regulação das populações de herbívoros tem sido tema de diversas pesquisas (Power 1992, Hunter et al 1997, Kindlmann & Dixon 2001, Nachman & Zemek 2003. Algumas pesquisas consideram os inimigos naturais como determinantes da abundância de herbívoros nas plantas (efeito "top-down") (Polis 1994, Pace et al 1999, Persson 1999.…”

Predators drive community structure in coral reef fish assemblages

“…Such ''top-down effects'' from predation may be mediated by or interact with ''bottom-up effects'' such as variation in primary production and nutrient supply. For many systems it is likely that both top-down and bottom-up effects interact to structure communities (Hunter et al 1997, Shurin et al 2010. Further, variations in habitat quality may interact to either ameliorate or exacerbate top-down effects, depending on the nature of habitat associations (Wilson et al 2008).…”

Opposing survivorship and fecundity effects of host phenology on the gall‐forming aphid Hormaphis hamamelidis

“…Host plant phenology affects the distribution and abundance of herbivores by producing temporal variation in host quality and quantity (Basset & Burckhardt, 1992;Floate et al, 1993;Hunter et al, 1997;Ishihara, 1998;Rossi et al, 1999). Insect herbivores often adapt to this temporal variation in resources by synchronising their life cycles with the phenologies of host plants (Ohgushi, 1991;Raffa et al, 1992;Yela & Herrera, 1993;Mopper & Simberloff, 1995;Matter et al, 1999;Gould & Sweet, 2000).…”