Habitat complexity effects on diversity and abundance differ with latitude: an experimental study over 20 degrees

Abstract

Habitat complexity is accepted as a general mechanism for increasing the abundance and diversity of communities. However, the circumstances under which complexity has the strongest effects are not clear. Over 20 degrees of Australia's east coast, we tested whether the effects of within-site structural habitat complexity on the diversity and community structure of sessile marine invertebrates was consistent over a latitudinal gradient where environmental conditions and species composition vary. We used experimental arrays with varied structural treatments to detect whether community cover, species richness, diversity and community composition (β-diversity) changed with increasing complexity. Community response to complexity varied over latitude due to differences in species richness and community development. Increased complexity had the greatest positive effects on community cover and species richness at higher latitudes where recruitment and growth were low. At lower latitudes, community cover and species richness were higher overall and did not vary substantially between complexity treatments. Latitudinal variation in within-treatment β-diversity relative to complexity further suggest divergent community responses. At higher latitudes, increased similarity in more complex treatments suggests community dominance of successful taxonomic groups. Despite limited effects on species richness and community cover at lower latitudes, β-diversity was higher in more complex treatments, signifying potential positive effects of increased complexity at these sites. These results demonstrate the context-dependency of complexity effects in response to variation in species richness and community development and should be taken into consideration to help direct conservation and restoration efforts.

A global analysis of complexity–biodiversity relationships on marine artificial structures

“…We predicted that patch-scale complexity would have a positive influence on the taxa richness and abundances of all sessile and mobile invertebrate functional groups but not algae, which have higher light requirements, because of greater shading in the crevices (Strain et al, 2020). Furthermore, we expected that the positive effects of increased complexity on richness and abundances of sessile and mobile invertebrates would increase with tidal elevation and with decreasing latitude, as desiccation stress and extreme high temperatures increase, respectively (Bracewell et al, 2018). Finally, we hypothesized that complexity would have a reduced effect on the richness and abundances of sessile and mobile invertebrates in highly polluted environments such as those located near marinas or ports, where the effects of pollution can over-ride the effects of complexity (Mayer-Pinto et al, 2016).…”

“…The environmental variation among sites at local and biogeographic scales may influence patch-scale habitat complexity (hereafter complexity)-biodiversity relationships by determining resource availability, environmental conditions, as well as the species pool on which complexity can act (Bracewell et al, 2018;Johnson et al, 2003).…”

“…The stress gradient hypothesis (Bertness & Callaway, 1994) proposes that positive interactions among species (e.g., between habitat-forming and dependent taxa) will be most prevalent in environmentally stressful environments, where local habitat amelioration is critical to organismal survival (Bracewell et al, 2018;McAfee et al, 2016). Hence, microhabitats that ameliorate extreme temperatures and/or desiccation stressors could increase in importance with increasing tidal elevation (Bateman & Bishop, 2016) and decreasing latitude (Bracewell et al, 2018). Conversely, the patch-scale effects of complexity may be consistent across latitude if the local species are adapted to their local conditions or could have a greater influence in locations where there is a greater difference between the air and sea temperatures.…”

“…Additionally, complexity may be expected to have greatest patch-scale effects on biodiversity in environments where there is a diverse species pool on which it can act, whereby, the effects of complexity may vary across latitudinal gradients in species richness (Bracewell et al, 2018). At local scales, anthropogenic stressors such as contaminants may over-ride the effects of complexity when they create conditions that are inhibitory to the survival of most species (Mayer-Pinto et al, 2016).…”

Environmental filtering underpins the island species—area relationship in a subtropical anthropogenic archipelago

“…greater habitat diversity, which enables a greater range of habitat specialists to exist on an island (Bracewell, Clark, & Johnston, 2018;Hortal, Triantis, Meiri, Thebault, & Sfenthourakis, 2009). Third, based on the equilibrium theory of island biogeography (IBT) (MacArthur & Wilson, 1963, 1967, larger islands sustain larger populations of species which reduces the probability of stochastic extinction (also known as ecological drift, Gilbert & Levine, 2017;Vellend, 2016).…”