On the relationships between size and abundance in plants: beyond forest communities

Abstract

The inverse relationship between size and abundance is a well‐documented pattern in forests, and the form of size–density relationships depends on the balance between growth and mortality rates in the community. Traditionally, studies of plant size distributions have focused on single‐species populations and forests, but here we examine diverse communities dominated by plants with varied life histories, including grasses, forbs, shrubs, and succulents. In particular, we test whether the parameters of the individual size distribution differ systematically across community types, whether they fit the contrasting predictions of metabolic or demographic theories, and whether they share a common cross‐community scaling relationship with forest communities and crop populations. All thirteen of our study sites better fit the predictions of demographic equilibrium theory, but interestingly, fits of both demographic and metabolic models showed little systematic variation across community types, despite large differences in environmental conditions and dominant life forms. Finally, analysis of the cross‐community scaling relationship demonstrates that natural and restored non‐forest communities conform to patterns of size and abundance observed among forest, plantation, and crop systems. Taken together, our results suggest that common ecological mechanisms govern plant community size structure across broad environmental gradients, regardless of the dominant plant life forms or limiting resources.

The sizes of life

“…Our inferred within-group size-biomass relationships ( Fig 2 ) appear reasonable, with fish and plant spectra being comparable to previous community-level results that are relatively well-studied [ 8 , 100 ]. Total biomass in the smallest size classes (<10 −16 g) is dominated by marine bacteria ( Fig 2AA ).…”

“…Withingroup biomass uncertainties are high among some taxa, especially in microbes [30]. Data and synthesis of within and between-study uncertainties on biomass that we base our study on remain crude across groups [30] but are consistent with estimates from independent studies on plant and fish [8,100,108]. We have also filled the important gaps of marine habitat builders [59,88,109,110] and incorporated latest estimates for subterranean microbes [96,111].…”

“…Cross-taxa size-biomass relationships are often described using power laws, with positive [10,13] or negative [8,[15][16][17] exponents resulting in extremely left or right-skewed distributions (where the body size with the maximum biomass is at the end of the size range). For plant communities where community-level sizebiomass relationships are better documented than other groups, the right-skewed Weibull distribution was used [100], which is a special case of the GEV. On the other hand, empirical studies on size-species frequency distributions, though not easily translatable to size-biomass spectra (except when all species have equal biomass), exhibit dome-shaped [130] and becomes less consistently right-skewed as one descends into finer taxonomic classifications [21,131], which are possibilities for size-biomass spectra that cannot be captured by power laws.…”

Energetic context determines species and community responses to ocean acidification

“…We did not find that biomass on the tiles significantly differed between treatments, despite differences in total cover. Perhaps the reduced density of competitors under the Thalassiosira diet and low pH conditions allowed the organisms that were present to feed more effectively, to maintain biomass (i.e., a size–abundance trade‐off; Dillon et al 2019). Although community secondary production has been shown to decline with acidification (Nagelkerken and Connell 2015), we did not find this response to be generally true, although there is a trend for communities fed with the Tetraselmis diet .…”

Abundance and spatial distribution analyses of Stemonoporus moonii Thwaites (Dipterocarpaceae) - a critically endangered species endemic to Sri Lanka

“…However, S. moonii was distributed well throughout their habitat. Resource allocation strategies prioritize the persistence of a species, allowing them to persist for a long period in their habitat below their maximum size (Dillon et al 2019).…”