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Baselga: [Partitioning the turnover and nestedness components of beta diversity. Global Ecology and Biogeography, 19, 134—143, 2010] proposed pairwise (β nes ) and multiple-site (β NES ) beta-diversity measures to account for the nestedness component of beta diversity. We used empirical, randomly created and idealized matrices to show that both measures are only partially related to nestedness and do not fit certain fundamental requirements for consideration as true nestedness-resultant dissimilarity measures. Both β nes and β NES are influenced by matrix size and fill, and increase or decrease even when nestedness remains constant. Additionally, we demonstrate that β NES can yield high values even for matrices with no nestedness. We conclude that βnes and βNES are not true measures of the nestedness-resultant dissimilarity between sites. Actually, they quantify how differences in species richness that are not due to species replacement contribute to patterns of beta diversity. Finally, because nestedness is a special case of dissimilarity in species composition due to ordered species loss (or gain), the extent to which differences in species composition is due to nestedness can be measured through an index of nestedness.

The nested subset pattern (nestedness) of faunal assemblages has been a research focus in the fields of island biogeography and conservation biology in recent decades. However, relatively few studies have described nestedness in butterfly assemblages in oceanic archipelago systems. Moreover, previous studies often quantified nestedness using inappropriate nestedness metrics and random fill algorithms with high Type I errors. The aims of this study are to examine the existence of nestedness and underlying causal mechanisms of butterfly assemblages in the Zhoushan Archipelago, China. We used the line-transect method to determine butterfly occupancy and abundance on 42 study islands from July to August 2014. We obtained butterfly life-history traits (wingspan, body weight and minimum area requirement) by field work and island geographical features (area and isolation) from the literature. We used the recently developed metric WNODF to estimate nestedness. Partial Spearman rank correlation was used to evaluate the associations of nestedness and island geographical features as well as butterfly life-history traits related to species extinction risk and colonization ability. The butterfly assemblages were significantly nested. Island area and minimum area requirement of butterflies were significantly correlated with nestedness after controlling for other independent variables. In contrast, the nestedness of butterflies did not appear to result from passive sampling or selective colonization. However, multi-year studies are needed to confirm that target effects are not muddling these results. Our results indicate that selective extinction may be the main driver of nestedness of butterfly assemblages in our study system. From a conservation viewpoint, we should protect both large islands and species with large area requirement to maximize the number of species preserved.

Nestedness is a widely studied pattern in ecology and biogeography. Nestedness has been termed perfect when sites harbouring low-diversity assemblages contain subsets of species in progressively more diverse assemblages. Nestedness has been studied in various regional and environmental contexts, but few studies have rigorously examined environmental factors underlying this pattern. We studied the degree and determinants of nestedness in insect assemblages of headwater streams. We hypothesized that nested habitat characteristics and nested niche structure generate nestedness in these organisms and tested this hypothesis in 8 boreal drainage basins (63–70° N, 23–29° E). Stream insect assemblages were significantly nested in all 8 regions based on the nestedness temperature calculator and in 5 regions based on discrepancy analysis. Nestedness was weak, however, as suggested by high matrix temperature values. Site ranks in the maximally packed nestedness matrix were significantly correlated to stream size in 2 of the regions and to environmental gradients in 5 of the regions. Nestedness was primarily governed by stream size and local environmental gradients. The relationships of nestedness to environmental gradients suggest that, at least in some regions, stream insects show nested niche structure with regard to their responses to environmental gradients. These environmental relationships are highly region-specific, however, suggesting strong context-dependency in nested subset patterns.

The number of monogenean gill parasite species associated with fish hosts of different sizes is evaluated for 35 host individuals of the West African cyprinid Labeo coubie. The length of host individuals explains 86% of the total variation in monogenean species richness among individuals. Larger hosts harbour more species than smaller ones. The existence of a hierarchical association of parasite species in individuals of L. coubie is demonstrated. Monogenean infracommunities on larger fish hosts consist of all species found on smaller hosts plus those restricted to the larger size categories, suggesting some degree of compositional persistence among host individuals. The findings provide strong support for an interpretation of the relationship between monogenean parasite species richness and host body size in terms of a nested species subset pattern, thus providing a new record of repetitive structure and predictability for parasite infracommunities of hosts.

In ecology, populations may be linked conceptually with landscapes through habitat and spatial population models. Usually, these models deal with single species and treat a range of uncertainties implicitly and explicitly. They assist managers in testing different management scenarios and making strategic decisions. Landscape pattern analysis was the first attempt to deal with multiple species, and it led to a range of landscape management strategies. Advances in landscape ecology, driven largely by the pragmatic needs of conservation, are building approaches to multispecies management that have stronger ecological foundations. However, their treatment of uncertainty is in its infancy. In this paper, we provide examples to illustrate some of these issues. We conclude that one of the most important sources of uncertainty is the choice of the modeling frame. We recommend that landscape planners use different kinds of models, identify important sources of uncertainty that may affect planning decisions, and seek options that are likely to result in tolerable outcomes, despite uncertainty.

Aim We compared assemblages of small mammal communities from three major desert regions on two continents in the northern hemisphere. Our objective was to compare these with respect to three characteristics: (1) species richness and representation of trophic groups; (2) the degree to which these assemblages exhibit nested community structure; and (3) the extent to which competitive interactions appear to influence local community assembly. Location We studied small mammal communities from the deserts of North America (N = 201 sites) and two regions in Central Asia (the Gobi Desert (N = 97 sites) and the Turan Desert Region (N = 36 sites), including the Kara-Kum, Kyzyl-Kum, NE Daghestan, and extreme western Kazakhstan Deserts). Method To provide baseline data we characterized each desert region in terms of alpha, beta, and gamma diversity, and in terms of the distribution of taxa across trophic and locomotory groups. We evaluated nestedness of these communities using the Nestedness Temperature Calculator developed by Atmar & Patterson (1993, 1995), and we evaluated the role of competitive interactions in community assembly and applied a null model of local assembly under varying degrees of competitive interaction (Kelt et al., 1995, 1996). Results All three desert regions have low alpha diversity and high beta diversity. The total number of species in each region varied, being highest in North America, and lowest in the Turan Desert Region. The deserts studied all present evidence of significant nestedness, but the mechanism underlying this structure appears different in North American and Asia. In North America, simulations strongly implicate interspecific competition as a dominant mechanism influencing community and assemblage structure. In contrast, data from Asian desert rodent communities suggest that these are not strongly influenced by competition; in fact, they have greater numbers of ecologically and morphologically similar species than expected. These results appear to reflect strong habitat selection, with positive associations among species that share similar habitat requirements in these communities. Our analyses support earlier reports suggesting that predation and abiotic forces may have greater influences on the assembly and organization of Asian desert rodent communities, whereas interspecific competition dominates assembly processes in North America. Additionally, we suggest that structuring mechanisms may be very different among the two Asian deserts studied. Gobi assemblages appear structured by trophic and locomotory strategies. In contrast, Turan Desert Region assemblages appear to be randomly structured with respect to locomotory strategies. When trophic and locomotory categories are combined, however, Turan species are positively and nonrandomly associated.