CiteULike: cmm Lewinsohn

On nestedness analyses: rethinking matrix temperature and anti-nestedness

Mario Almeida-Neto — 2007-04-03T20:37:01-00:00

Oikos, Vol. 116, No. 4. (2007), pp. 716-722.

The analysis of nested structures in sets of species assemblages across different sites or in networks of interspecific interactions has become common practice in ecological studies. Although new analyses and metrics have been proposed, few studies have scrutinized the concepts that subtend nestedness analysis. We note two important conceptual problems that can lead to terminological inconsistencies and flawed interpretations. First, the thermodynamic analogy that underlies the most common metric of nestedness, matrix temperature, is flawed and has led some authors to incorrect interpretations. Second, the term "anti-nestedness" is a potential source of confusion and inconsistencies. We review four concepts for anti-nestedness and examine how distinct they are. "Anti-nested" matrices, i.e. less nested than expected by chance, may result from different ecological processes and show distinct structural patterns. Thus, there is no single unequivocal opposite of nestedness to be represented as "anti-nestedness". A more profitable approach is to designate and test each distinct non-nested pattern according to its specific assumptions and mechanistic hypotheses.

Structure in plant-animal interaction assemblages

Thomas Lewinsohn — 2006-02-18T13:56:39-00:00

Oikos, Vol. 113, No. 1. (April 2006), pp. 174-184.

Compartments in insect-plant associations and their consequences for community structure

Paulo Prado — 2006-02-19T02:04:46-00:00

Journal of Animal Ecology, Vol. 73, No. 6. (2004), pp. 1168-1178.

Summary 1. Compartmentation has been less explored than other forms of community structure. We assessed compartmentation of associations between insects and plants on a regional scale, and analysed some of its causes and consequences. The data set used was the host records of fruit flies (Diptera; Tephritidae) that breed in flowerheads of plants of the tribe Vernonieae (Asteraceae) in the Espinhaco Mountain range, Minas Gerais, Brazil. This data set was obtained with a consistent sampling protocol and is taxonomically fully resolved. 2. The binary association matrix had a total of 35 insect and 81 plant species. Most of the insects were specialized on plants of a single subtribe, genus or species group. Correspondence analysis showed that the association matrix is divided in six well-delimited compartments of insects specialized on subtribes or genera of plants. 3. Host dissimilarity among insects and insect dissimilarity among plants were expressed as Jaccard distances. Tests with a multi-response permutation procedure (MRPP) showed that both kinds of dissimilarities were higher among compartments than within them. 4. Monte Carlo randomizations were used to compare matrix parameters with values expected in the absence of compartments. In 4000 runs, the number of insect species that shared at least one host plant (ecological neighbours) was smaller than expected. Nevertheless, mean host similarity among insects, and the proportion of exclusive host plants used by each insect species did not differ from null model predictions. Host similarity of insects with their nearest neighbours in niche space was higher than expected by the null model. On the other hand, host similarity with farthest neighbours was lower than expected. 6. The observed compartmentation of insect/plant associations can be ascribed to the marked specialization of flowerhead tephritids, and allows the reduction of diffuse competition among insects. However, compartmentation did not decrease overall niche overlap among insects because reduction in number of neighbours is offset by increased overlap with species in the same compartment. Therefore, the pattern in this system cannot be derived from resource partitioning alone