[show abstract][hide abstract] ABSTRACT: Despite edges being common features of many natural habitats, there is little general understanding of the ways assemblages respond to them. Every edge between two contrasting habitats has characteristics governed by the composition of adjoining habitats and/or by the nature of any transitions between them. To develop better explanatory theory, we examined the extent to which edges act independently of the composition of the surrounding landscape and to which transitions between different types of habitats affect assemblages. Using experimental landscapes, we measured the responses of assemblages of marine molluscs colonising different experimental landscapes constructed with different compositions (i.e. different types of habitats within the landscape) and different types of transitions between habitats (i.e. sharp vs gradual). Edge effects (i.e. proximity to the edge of the landscape) were independent of the internal composition of experimental landscape; fewer species were found near the edges of landscapes. These reductions may be explained by differences in differential larval settlement between edges and interiors of experimental landscapes. We also found that the sharpness of transitions influenced the magnitude of interactions in the different types of habitats in experimental landscapes, most probably due to the increased number of species in areas of transition between two habitats. Our experiments allowed the effects of composition and transitions between habitats to be disentangled from those of proximity to edges of landscapes. Understanding and making predictions about the responses by species to edges depends on understanding not only the nature of transitions across boundaries, but also the landscape in which the edges are embedded.
PLoS ONE 01/2013; 8(4):e61349. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Loss of habitat is commonly identified as a reduction in area (or patch size) and its effects are often investigated using species−area relationships to evaluate loss of biodiversity. In many habitats, however, area alone is not sufficient to explain the decline of populations because natural habitats are rarely homogeneous. In fact, reductions in the diversity of habitats (e.g. destruction of microhabitats) might have even greater effects on the diversity of assemblages. Although these are 2 well-known attributes of habitats (i.e. area and diversity), there have been few empirical studies that have attempted to separate their effects by experimental manipulation. Experiments were carried out to separate the effects of number, relative proportion and identity of patches of habitat using additive designs. Predictions were tested using assemblages of marine molluscs colonizing artificial mimics of macroalgal habitats on rocky intertidal platforms. Our experiments to disentangle different attributes of habitat heterogeneity showed that these are complex and highly interactive. In particular, not all heterogeneous habitats had the numbers of species expected from a simple species−area relationship. Instead, the presence of more species in heterogeneous habitats could, to a great extent, be explained by the presence or absence of particular types of sub-habitats and not just by patch size. The complexity we found in responses of assemblages to composition of heterogeneous habitats was not predicted and could not have been observed without appropriate manipulations of habitat composition. A mechanistic understanding of the associations between species and particular types of habitats is essential for better predictions of species’ responses to loss of natural habitats.
Marine Ecology Progress Series 01/2011; 437:135-145. · 2.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: A fundamental problem in ecology, regardless of habitat or system, is understanding the relationship between habitats and assemblage of organisms. It is commonly accepted that differences in composition and surrounding landscape of habitats affect the diversity of assemblages, although there is not much empirical evidence because of difficulties of manipulating structure in many habitats. These relationships were examined experimentally, using habitats of artificial turfs that are colonized by diverse assemblages of gastropods. Each habitat was made of nine sub-habitats, which were sampled individually to allow tests of hypotheses about the effect of type of habitat and the influence of other adjacent sub-habitats on the colonizing assemblage. Turf habitats were deployed for 8 weeks on a rocky shore after which they were collected and the colonizing assemblages of gastropods sampled. Independently of the types of turfs combined to form different habitats, there were more species where there was more than one type of component in a habitat (i.e. structural diversity). The type of habitat (i.e. structural identity) itself had little or no influence on the colonizing assemblage. The number of species colonizing short-sparse and short-dense turfs was influenced by which type of habitat was adjacent. Thus, when units of one type (e.g. short-sparse turf) were added to a patch of habitat of long-sparse turfs, the number of species in short-sparse turfs was greater than in patches of the same type. This also increased total number of taxa in the whole patch of habitat. These results show how diversity of gastropods colonizing heterogeneous patches of habitat is influenced not only by the number of types of sub-habitats, but also by interactions with surrounding sub-habitats. These findings reiterate the importance of investigating the role of structure of habitats and of their surrounding landscapes across different systems, irrespective of their size or associated assemblages of organisms.
[show abstract][hide abstract] ABSTRACT: Despite a long history of work on relationships between area and number of species, the details of mechanisms causing patterns have eluded ecologists. The general principle that the number of species increases with the area sampled is often attributed to a sampling artifact due to larger areas containing greater numbers of individuals. We manipulated the patch size and surface area of experimental mimics of macro-algae to test several models that can explain the relationship between abundance and species richness of assemblages colonizing different habitats. Our results show that patch size and structural complexity have independent effects on assemblages of macroinvertebrates. Regardless of their structural complexity, larger habitats were colonized by more species. Patch size did not have a significant effect on numbers of individuals, so the increased number of species in larger habitats was not simply a result of random placement associated with sampling increased number of individuals. Similarly, random placement alone could not explain differences in numbers of species among habitats with different structural complexity, contrary to suggestions that the relationship between number of species and surface area might also be a sampling artifact due to more complex habitats having larger areas and therefore sampling more individuals. Future progress would benefit from manipulating properties of habitat in conjunction with experimental manipulations of area.
[show abstract][hide abstract] ABSTRACT: 1. The nature and resources supplied by different components of habitats influence species, creating variability from place to place within a habitat. 2. Experiments were done to investigate the effects of altering components of habitats on the variability of assemblages of numerous species of intertidal gastropods. 3. Artificial habitats with three levels of structure, combining different types of turf (i.e. different densities and height of fronds) were sampled 8 weeks after deployment in the intertidal. They were rapidly colonized by up to 66 species of gastropods. 4. Independently of the types of turf combined to form different habitats, there were differences in assemblages where there was more than one type of component present. Multivariate dissimilarities among units making up each habitat were also greater where there were more than one type of unit, but there was no such difference in the variance of numbers of species per unit. 5. Altering the relative abundances of different types of components made little change to the assemblages, nor their multivariate variability among units of habitat and the variance in number of species per unit in each habitat. 6. Differences in assemblages due to the different structure of habitat are complex to interpret and simple characterizations of structure of habitat are inadequate. Comparing different habitats requires appropriate experimentation to ensure that variability within habitats is also investigated.
Journal of Animal Ecology 10/2007; 76(5):986-94. · 4.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Investigating the context that surrounds each habitat is crucial to understand local responses of assemblages of species to habitats. Here, I tested whether responses of benthic macroinvertebrates to the structural complexity of experimental habitats were mediated by the characteristics of their surrounding habitats (i.e. rockpools or emergent-rock surfaces). Each type of surrounding habitat provided particular biotic (e.g. algal growth) and abiotic (e.g. temperature, water movement) conditions that were expected to affect benthic assemblages. The results show that (1) composition of entire assemblages was affected by the matrix and type of habitat; (2) effects of the matrix on the number of species varied depending on the different types of habitats; (3) abundant species showed specific responses to type of habitat, independently of the matrix; and (4) relationships between numbers of species and two major environmental variables (i.e. micro-algal biomass and sediment) varied depending on the type of habitats and the surrounding matrix. Generally, these findings demonstrate that understanding the consequences of the spatial structure of these habitats is essential to advance our knowledge on patterns of abundance and distributions of functionally important species and ultimately the structure of intertidal assemblages.