Too much of a good thing: Shrub benefactors are less important in higher diversity arid ecosystems

Abstract

The biodiversity–ecosystem function literature provides a useful framework to examine many processes associated with species diversity in ecology. One such context is the maintenance of biodiversity by facilitation in arid ecosystems. Here, we examined the complex interactions between local plant species richness and the intensity of shrub facilitation for maintaining biodiversity in arid plant communities. A synthesis including a meta‐analysis was used to compile nearly 600 papers on positive interactions mediated by shrubs in dryland plant communities (search terms: shrub, positive, facilitat*) to examine whether interactions in these studies changed with reported local species richness. A total of 19 studies and 141 independent instances directly examined and reported facilitation of diversity measures in naturally assembled plant communities and provided estimates of local species richness. Synthesis. The net effect of increasing local plant species richness was negative and shifted the relative frequency of interactions with shrubs from positive to negative with increasing local species richness. This relationship suggests that increases in richness do not always enhance functions that maintain diversity in plants communities likely due to concurrent increases in the indirect negative interactions between species under shrubs or in changes in the local species pool.

The relative effects of artificial shrubs on animal community assembly

“…Ephedra californica also have the potential to act as foundational species within these ecosystems. These foundational species typically exert facilitative interactions with both plant and animal communities (Brewer et al 2021;Lortie et al 2021;Zuliani et al 2021Zuliani et al , 2023a. Foundational shrub species promote the recruitment and association of vertebrates primarily through temperature amelioration, as several species within desert ecosystems will utilize the microclimate produced by shrub canopies to thermoregulate (Attum et al 2013;Ivey et al 2020Ivey et al , 2022Zuliani et al 2023b).…”

Coping with changing plant–plant interactions in restoration ecology: Effect of species, site, and individual variation

“…Plant–plant interactions may shift from facilitation to competition (and vice versa) depending on the ecological context (see recent reviews Lortie et al, 2021; Soliveres et al, 2015 and references therein). Here, we found variation in Chamaerops humilis –woody species interactions at three levels: plant community, study site, and inter‐block.…”

Shrub density effects on the presence of an endangered lizard of the Carrizo Plain National Monument, California

“…Ephedra californica is the dominant shrub species within the Elkhorn Plain in the Carrizo Plain National Monument in San Luis Obispo County, CA, USA (35.11982, −119.62853) (Lortie, Filazzola, et al, 2021 ). Ephedra californica can reach heights of up to 1 m and typically takes 5–10 years to reach 0.5 m in size, suggesting that its cover and density changes over a longer period (Cutler, 1939 ; Filazzola et al, 2020 ; Lortie, Zuliani, et al, 2021 ). With numerous twigs and needle‐like leaves, this species possesses unique characteristics of both gymnosperms and angiosperms, making it well‐adapted to its native semi‐arid and arid environments (Loera et al, 2012 ).…”