Trait‐mediated environmental filtering drives assembly at biogeographic transition zones

Abstract

Abiotic filtering is a major driver of gradients in the structure and functioning of ecosystems from the tropics to the poles. It is thus likely that environmental filtering is an important assembly process at the transition of biogeographical zones where many species occur at their range limits. Shifts in species abundances and association patterns along environmental gradients can be indicative of environmental filtering, which is predicted to be stronger in areas of high abiotic stress and to promote increased similarity of ecological characteristics among co-occurring species. Here we test these hypotheses for scleractinian corals along a broad latitudinal gradient in high-latitude eastern Australia, where corals occur at the margins of their ranges and environmental tolerances. We quantify variation in taxonomic, zoogeographic, and functional patterns combined with null model approaches and demonstrate systematic spatial variation in community structure and significant covariance of species abundance distributions and functional characteristics along the latitudinal gradient. We describe a strong biogeographic transition zone, consistent with patterns expected under abiotic filtering, whereby species are sorted along the latitudinal gradient according to their tolerances for marginal reef conditions. High-latitude coastal reefs are typified by widely distributed, generalist, stress-tolerant coral species with massive and horizontally spreading morphologies and by diminishing influence of tropical taxa at higher latitudes and closer to the mainland. Higher degree of ecological similarity among co-occurring species than expected by chance supports the environmental filtering hypothesis. Among individual traits, the structural traits corallite size and colony morphology were filtered most strongly, suggesting that characteristics linked to energy acquisition and physical stability may be particularly important for coral survival in high-latitude environments. These findings highlight interspecific differences and species interactions with the environment as key drivers of community organization in biogeographic transition zones and support the hypothesis that environmental filters play a stronger role than biotic interactions in structuring ecological communities in areas of high abiotic stress.

Coral Community Structure and Recruitment in Seagrass Meadows

“…Golbuu et al, 2016), reduced pH has been shown to limit the abundance (Price et al, 2012) and diversity (Fabricius et al, 2011;Crook et al, 2012) of calcifying organisms at other locations. In the present study, pH at the seagrass sites routinely dropped to values considered unfavorable for most corals (e.g., <7.8, Figure 2; see also Camp et al, 2016a), and therefore may have resulted in environmental filtering against some coral species (Sommer et al, 2014). The ability to tolerate reduced pH varies among coral species (McCulloch et al, 2012), and importantly, low pH appears to inhibit settlement of Acropora palmata, potentially through alteration of larval settlement processes or chemical settlement cues from crustose coralline algae (Albright et al, 2010).…”

Species Sorting of Benthic Invertebrates in a Salinity Gradient – Importance of Dispersal Limitation

“…In nature, community assembly may result from several interacting factors like species—environment relationships together with stochastic dispersal and demographic processes [9]. Chase [6] suggested from experiments that the relative importance of dispersal and niche processes will depend on the harshness of the environmental filter, and the interaction between the environment and dispersal may also be influenced by species functions or ecological traits [7, 10]. For instance, differences in dispersivity traits were of major importance for community assembly in metacommunities [11, 12], which by definition are communities connected by dispersal [4].…”

High Latitude Corals Tolerate Severe Cold Spell

“…Low temperatures, low light availability and high attenuation in winter, low aragonite saturation and high competition with seaweeds are pervasive stressors for corals in these environments (Miller, 1995;Miller and Hay, 1996;Kleypas et al, 1999;Sommer et al, 2017). These stressors filter species so that high latitude coral communities are largely dominated by corals which are generalists with broad niche requirements (Sommer et al, 2014;Keith et al, 2015;Mizerek et al, 2016). The stress tolerant nature of most high latitude species could thus explain the low impact of the 2016 MCS.…”

“…These species are largely generalists with broad niche requirements (Sommer et al, 2014;Keith et al, 2015;Mizerek et al, 2016), and they regularly experience temperatures that are considered "cold" (<18 • C), for these inherently tropical taxa (Veron, 1995). Although resilient, these corals are not impervious to the stressful conditions at high latitudes.…”