Download Appendix S1: Literature review on Habitat Structure–Species

Appendix S1: Literature review on Habitat Structure–Species Diversity relationships:
methods and results
Methods
In an earlier review (Tews et al. 2004), 85 empirical papers published in 1960–2003 were
surveyed. We revisited 70 of these for which we had online access, and went on to study 199
articles published in 2004–2013. The survey for both periods was selective in nature in a
number of respects. Firstly, it was restricted to studies of animal species diversity, even
though vegetation profiles are also relevant to plants, such as bromeliads segregated into
different vertical niches. An extensive literature exists on plant species diversity in relation to
heterogeneity of habitat patches. Secondly, the literature survey was restricted to the
terrestrial environment and, furthermore, heterogeneity in relation to vegetation
characteristics, land covers and topographic relief. Hence, marine, intertidal and freshwater
systems were not included, nor studies with a focus on urban or geological structures as
habitat. Thirdly, the survey was based on a Web of Science search using a set number of
topic keywords, being considered as equivalent terms describing habitat structure. These
were: habitat heterogeneity, habitat complexity, habitat diversity, structural diversity,
structural complexity, structural heterogeneity, spatial heterogeneity, spatial complexity,
foliage height diversity, foliage diversity, architectural complexity, vegetation complexity,
vegetation heterogeneity. Studies looking at either species diversity or species richness
patterns were included, but not those that focussed on species assemblage rather than species
number. Fourthly, articles were only included if they included quantified measures of habitat
structure.
For each article, we recorded the following: the species group, ecosystem, principal
climate type (tropical vs. temperate), effect of habitat structure, term used for habitat
structure, and how and at what scale it was measured. We also noted any particularly novel
evidence and explanations for causal links, as well as the use of experimentation and remote
sensing (beyond the use of existing land cover/vegetation maps derived from satellite
imagery). Habitat attributes were categorised into 15 types (Table 1 of article). The scale of
measurement was recorded as the area within which measurements were taken to generate
one value for the habitat structure variable in question. Depending on the nature of the
variable, this was sometimes one measurement or observation (e.g. density of trees, estimated
canopy cover) or else multiple measurements from which a statistic was computed (e.g.
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contacts of foliage with vertical pins). Of underlying interest was the likelihood that the
attribute, and the scale at which it was measured, could be retrieved using airborne lidar.
Results
Here we focus in the literature of 2004–2013, making comparisons where relevant with the
earlier period of 1960–2003 covered by the review of Tews et al (2004). Some 70% of the
199 papers published between 2004 and 2013 that met the criteria for the literature search
came from temperate (including Mediterranean/warm temperate/sub-tropical) zones; 25%
were situated in the tropics, and 5% encompassed both. ‘Habitat heterogeneity’ was by far the
most common term (43% of those used), continuing the trend of increasing usage since the
1960s/70s observed by Tews et al. (2004). ‘Habitat diversity’ (14%) and ‘habitat complexity’
(12%) were the next most applied terms. ‘Landscape heterogeneity’ and ‘landscape
complexity’ entered the lexicon in a significant way, reflecting an increased emphasis on
larger scales of study (see below).
In 2004–2013 there continued to be a disproportionate emphasis on vertebrates in
general (53%) and birds in particular (30%), when compared to their share of the global
species richness (3 and 0.6% of described species respectively; Groombridge & Jenkins
2000) (Figure S1a, Table S1). All but one of the invertebrate research papers (47%) were on
arthropods, the exception being a study of land snails in Greece (Triantis et al. 2005). In the
literature of 1960–2003, arachnids were the most studied arthropods, a particular focus being
on species-specific spider web heights, and how these are supported by plant architectural
forms, as a major organizing principle of species assemblages (Greenstone 1984). In the
2004–2013 publications, beetles (20% of invertebrates) took over as the most studied group
(Figure S1b). Arachnids (16%) and lepidoptera (11%) were again well represented, as were
ants (12%) and other hymenoptera (14%). The relative emphasis on vertebrates and
invertebrates shifted between the main ecosystem types that were the focus of the studies
(Figure S1c). For forest and woodland (35% of all papers), the majority of the studies (51%)
looked at invertebrates, whilst over a third were on birds and the rest on other vertebrates
(11%). This represents a shift from the period 1960–2003 when birds were the most studied
forest taxonomic group. For agricultural habitats (15% of all studies), birds (48%) and
invertebrates (45%) were almost equally well studied groups, with mammals and herptiles
being very poorly studied. A range of other ecosystems were dealt with, most commonly
steppes, prairies and other grasslands (12%) (Figure S1d). Almost a third of the total
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literature did not focus down on particular ecosystems, and this again reflects the increased
interest in species richness patterns at macroscales.
References
Greenstone, M.H. (1984) Determinants of web spider species diversity: vegetation structural
diversity vs. prey availability. Oecologia, 62, 299–304.
Groombridge, B. & Jenkins, M. (2000) Global Biodiversity: Earth’s Living Resources in the
21st Century. Cambridge University Press, Cambridge, UK.
Tews, J., Brose, U., Grimm, V., Tielborger, K., Wichmann, M.C., Schwager, M. & Jeltsch, F.
(2004) Animal species diversity driven by habitat heterogeneity / diversity: the
importance of keystone structures. Journal of Biogeography, 31, 79–92.
Triantis, K.A., Mylonas, M., Weiser, M.D., Lika, K. & Vardinoyannis, K. (2005) Species
richness, environmental heterogeneity and area: a case study based on land snails in
Skyros archipelago (Aegean Sea, Greece). Journal of Biogeography, 32, 1727–1735.
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