Generality in ecology: testing North American grassland rules in South African savannas

Abstract

Ecology has emerged as a global science, and there is a pressing need to identify ecological rules – general principles that will improve its predictive capability for scientists and its usefulness for managers and policy makers. Ideally, the generality and limits of these ecological rules should be assessed using extensive, coordinated experiments that ensure consistency in design and comparability of data. To improve the design of these large‐scale efforts, existing data should be used to test prospective ecological rules and to identify their limits and contingencies. As an example of this approach, we describe prospective rules for grassland responses to fire and rainfall gradients, identified from long‐term studies of North American grasslands and tested with existing data from long‐term experiments in South African savanna grasslands. Analyses indicated consistent effects of fire on the abundance of the dominant (grasses) and subdominant (forbs) flora on both continents, but no common response of grass or forb abundance across a rainfall gradient. Such analyses can inform future research designs to refine and more explicitly test ecological rules.

Convergence and contingency in production–precipitation relationships in North American and South African C4 grasslands

“…We also explore more fully purported diVerences in interannual variability in climatic regimes and ANPP between North American and South African grasslands. Mesic grasslands in North America and South Africa are quite similar structurally; C 4 grasses (NADP-ME subtype, Sage and Monson 1999) dominate the herbaceous layer, with the abundance of C 3 shrubs and trees dependent on Wre and grazing history (Scholes and Archer 1997;Knapp et al 1998;du Toit et al 2003;Knapp et al 2004). Moreover, in these two long-term study sites, mean annual precipitation was nearly identical, and growing season length, temperature, and precipitation amount were also similar ( Fig.…”

Plant community response to loss of large herbivores differs between North American and South African savanna grasslands

“…Multiple disturbances shape herbaceous plant community composition and dynamics of mesic (.500 mm MAP [mean annual precipitation] in the tropics and .600 mm MAP outside the tropics; Bond et al 2003) grasslands and savannas globally, hereafter referred to as savanna grasslands (sensu Scholes and Walker 1993), with fire and grazing considered key, shared drivers of these systems (Knapp et al 2004). Moderate grazing by large herbivores generally increases plant community diversity in mesic savanna grasslands, subject to various contingencies, such as climate, productivity, grazing intensity, and herbivore diversity (Milchunas et al 1988, Olff and Ritchie 1998, Bakker et al 2006.…”

“…Comparative studies focusing on the implications of large-herbivore loss and how these impacts vary with alterations in fire regime are lacking, particularly in savanna grasslands that differ in large-herbivore assemblages. Yet, such studies are critical for gaining a more general understanding of the global-scale impacts of modified disturbance regimes (Knapp et al 2004).…”

Generalities in grazing and browsing ecology: using across-guild comparisons to control contingencies

“…Controlling such contingencies can require large-scale replication using global research networks to standardize multiple local studies for testing postulated generalities in community-level patterns (adler et al 2011). another approach is to make comparisons across similar ecosystem types on different continents (Knapp et al 2004) or even across marine and terrestrial ecosystems (webb 2012), with the one ecosystem serving as the "control" for the other. For example, it has been found helpful to compare marine and terrestrial predatorprey systems to identify universal behavioral responses by which prey animals reduce their risk of predation (wirsing and Ripple 2011).…”