An experimental test of the response of macroecological patterns to altered species interactions

Abstract

Abstract. Macroecological patterns such as the species-area relationship (SAR), the species-abundance distribution (SAD), and the species-time relationship (STR) exhibit regular behavior across ecosystems and taxa. However, determinants of these patterns remain poorly understood. Emerging theoretical frameworks for macroecology attempt to understand this regularity by ignoring detailed ecological interactions and focusing on the influence of a small number of community-level state variables, such as species richness and total abundance, on these patterns. We present results from a 15-year rodent removal experiment evaluating the response of three different macroecological patterns in two distinct annual plant communities (summer and winter) to two levels of manipulated seed predation. Seed predator manipulations significantly impacted species composition on all treatments in both communities, but did not significantly impact richness, community abundance, or macroecological patterns in most cases. However, winter community abundance and richness responded significantly to the removal of all rodents. Changes in richness and abundance were coupled with significant shifts in macroecological patterns (SADs, SARs, and STRs). Because altering species interactions only impacted macroecological patterns when the state variables of abundance and richness also changed, we suggest that, in this system, local-scale processes primarily act indirectly through these properties to determine macroecological patterns.

How species richness and total abundance constrain the distribution of abundance

“…Instead, ecological processes may influence emergent patterns indirectly through their influence on constraints or state variables (Supp et al . ; White et al . ).…”

“…) and experimental (Supp et al . ) studies. However, even when these approaches successfully characterize empirical patterns, they do not indicate that ecological processes are not operating.…”

Species‐level and community‐level responses to disturbance: a cross‐community analysis

“…Clearly, changes in the list of species present and how abundance is divided among those species could impact any metrics using this information. However, experimental and observational studies suggest that changes in composition may not always scale up to impact community-level properties (e.g., Harte 2011, Supp et al 2012. This creates the possibility that disturbances that influence species may not influence higher levels of biological organization.…”

An experimental investigation of top–down effects of consumer diversity on producer temporal stability

“…Such top–down effects were likely driven by differences in overall levels of granivory on treatment plots, with the highest level of granivory on C plots (because kangaroo rats were only present on C plots), followed in order by ‐D, and then ‐R plots because quadrupedal mice abundance and diversity were similar on ‐D and C plots during the years studied (Thibault et al, ). Experimental reduction in rodent granivory likely enhanced annual plant seed survival explaining the higher abundance of total plants on Dipodomys and all rodent removal plots (Supp, Xiao, Ernest, & White, ). The increase in large‐seeded E. cicutarium abundance on such plots can also explain the concomitant decrease in annual plant richness and diversity because this exotic is known to competitively suppress natives: experimental removal of E. cicutarium is known to result in higher abundance and diversity of native annuals (Ignace, & Chesson, ; Schutzenhofer & Valone, ).…”