Assembly rules in Muscid Fly assemblages in the grasslands Biome of Southern Brazil

Abstract

-The distribution of muscid species (Diptera) in grasslands fragments of southern Brazil was assessed using null models according to three assembly rules: (a) negatively-associated distributions; (b) guild proportionality; and (c) constant body-size ratios. We built presence/absence matrices and calculated the C-score index to test negatively-associated distributions and guild proportionality based on the following algorithms: total number of fi xed lines (F L ), total number of fi xed columns (F C ), and the effect of the average size of the populations along lines (W) for 5000 randomizations. We used null models to generate random communities that were not structured by competition and evaluated the patterns generated using three models: general, trophic guilds, and taxonomic guilds.All three assembly rules were tested in each model. The null hypothesis was corroborated in all F L X F C co-occurrence analyses. In addition, 11 analyses of the models using the W algorithm showed the same pattern observed previously. Three analyses using the W algorithm indicated that species cooccurred more frequently than expected by chance. According to analyses of co-occurrence and guild proportionality, the coexistence of muscid species is not regulated by constant body size ratios. In fl ies of the grasslands, no rule was identifi ed. Yet, a consensus did emerge from our analyses: species co-occur more frequently than expected by chance, indicating that aggregation is a recurring phenomenon among fl ies with saprophagous adults and predatory larvae. Therefore, competition does not seem to play an important role in the determination of muscid assemblages in the grasslands in Southern Brazil.

Assembly patterns of mixed‐species avian flocks in the Andes

“…; Weiher & Keddy ; Hubbell ), a wide variety of local to regional‐scale studies have provided evidence that competitive interactions among species can be a major driver of the assembly of biotic communities (e.g. Gotelli & McCabe ; Krüger, de Carvalho & Ribeiro ), and species interactions, in particular competition, may mediate the assembly of communities from local (Cardillo, Gittleman & Purvis ; Cooper, Rodríguez & Purvis ) to regional spatial scales (Gotelli, Graves & Rahbek ). Comparatively little work has been conducted in social systems such as mixed‐species flocks, which are known to be strongly influenced by competitive interactions (Graves & Gotelli ).…”

“…insectivores and frugivores), we did not find evidence of constant body‐size ratios. Patterns of greater variances suggest that, in general, Andean mixed‐species flocks contained aggregations of relatively small or large species (Krüger, de Carvalho & Ribeiro ). Thus, some groups of birds may show aggregation in sizes within flocks, instead of more constant body‐size ratio spacing.…”

“…the C‐score should be significantly larger than expected by chance; Gotelli & McCabe ; Sanders et al . ; Krüger, de Carvalho & Ribeiro ). This index supports the fifth assembly rule by Diamond (), ‘Some pairs of species never coexist, either by themselves or as part of a larger combination’.…”

“…In this case, a flock structured by competition should present species with differences in size with a minimum overlap (Krüger, de Carvalho & Ribeiro ), becoming a mechanism allowing coexistence of apparently similar species (Dayan & Simberloff ). Two metrics, the minimum size ratio and the variance of size ratio, were calculated between the body lengths (i.e.…”

Temporal segregations in the surface community of an ephemeral habitat: Time separates the potential competitors of coprophilous Diptera

“…meditabunda ) and Sc. stercoraria are negatively affected by higher temperatures and therefore occur primarily during cooler spring and autumn (Hammer ; Blanckenhorn et al ; Kruger et al ).…”