Habitat complexity is touted as the mechanism for high-functionality in a variety of ecosystems, yet measuring habitat complexity is difficult and studies rarely agree in methodology. This paper addresses the use of habitat complexity in research from terrestrial, freshwater, and marine systems. The goal of the study is to provide a systematic review of methods of measuring habitat complexity, and recommendations that will allow ecologists to move towards an agreement of methods or a means of providing relevant information so that measures of habitat complexity can be compared between studies and between systems.
To review habitat complexity studies we searched ISI Web of Science with the search term “habitat complexity” for peer-reviewed literature published in a 33 year period, 1985-2018. Papers were included that attempted to quantify or categorize habitat complexity. From each study we recorded the habitat or system (marine, freshwater, terrestrial) and methodologies used to quantify habitat complexity. We also present a meta-regression of studies using fractal dimension to assess the relationship between habitat complexity and a biological response (typically biomass or species diversity), and to assess if that relationship changes depending on system studied or the scale of habitat complexity.
Results/Conclusions
Preliminary results are described for the literature review 1985-2014. Habitat complexity study publication rates increased in the early 2000s. Studies from marine habitats accounted for 53% of all habitat complexity studies examined; the rest of the studies were evenly split between freshwater and terrestrial habitats, with only 0.5% of studies including habitats from multiple systems. The most frequently used method for documenting habitat complexity in all systems was categorization of natural habitat types (ex. from most to least complex, high-relief reef, low-relief reef, sand), which accounted for 26% of all methods used across systems. Fractal dimension is a quantitative metric which is used across systems and has the potential to be comparable between systems, but only if the scale of habitat complexity (ex. the size of the organisms using the habitat) is accounted for. Defining habitat complexity in the context of the organisms using the habitat will likely allow for direct comparison of habitat complexity across marine, freshwater, and terrestrial habitats. This use of habitat complexity metrics over a broader scale will advance the theory and help researchers understand the mechanism by which habitat complexity contributes to species distribution and persistence.