S. F. Dos Reis

The nested assembly of individual-resource networks.

1. Much of the current understanding of ecological systems is based on theory that does not explicitly take into account individual variation within natural populations. However, individuals may show substantial variation in resource use. This variation in turn may be translated into topological properties of networks that depict interactions among individuals and the food resources they consume (individual-resource networks). 2. Different models derived from optimal diet theory (ODT) predict highly distinct patterns of trophic interactions at the individual level that should translate into distinct network topologies. As a consequence, individual-resource networks can be useful tools in revealing the incidence of different patterns of resource use by individuals and suggesting their mechanistic basis. 3. In the present study, using data from several dietary studies, we assembled individual-resource networks of 10 vertebrate species, previously reported to show interindividual diet variation, and used a network-based approach to investigate their structure. 4. We found significant nestedness, but no modularity, in all empirical networks, indicating that (i) these populations are composed of both opportunistic and selective individuals and (ii) the diets of the latter are ordered as predictable subsets of the diets of the more opportunistic individuals. 5. Nested patterns are a common feature of species networks, and our results extend its generality to trophic interactions at the individual level. This pattern is consistent with a recently proposed ODT model, in which individuals show similar rank preferences but differ in their acceptance rate for alternative resources. Our findings therefore suggest a common mechanism underlying interindividual variation in resource use in disparate taxa.

Larval aggregation and competition for food in experimental populations of Chrysomya putoria (Wied.) and Cochliomyia macellaria (F.) (Dipt., Calliphoridae)

In blowflies, larval aggregation in patches of food can be both intra‐ and interspecific, depending upon the degree to which competitors are clumped among the patches. In the present study, the implications of spatial aggregation for larval competition was investigated in experimental populations of the introduced blowfly Chrysomya putoria and the native Cochliomyia macellaria, using data from survival to adulthood in a range of single‐ and double‐species larval cultures. The reduction in C. macellaria survival rate in the presence of C. putoria suggests that the former species is the inferior competitor. The results on survival to adulthood for both species in single‐ and double‐species cultures can be explained in the light of the relationship between the level of intra‐ and interspecific aggregation and the efficiency of the larval feeding process. The possible implications of these results for the population biology of both species in natural environments are discussed.

Patterns of cranial shape diversification during the phylogenetic branching process of New World monkeys (Primates: Platyrrhini)

One of the central topics in evolutionary biology is understanding the processes responsible for phenotypic diversification related to ecological factors. New World monkeys are an excellent reference system to investigate processes of diversification at macroevolutionary scales. Here, we investigate the cranial shape diversification related to body size and ecology during the phylogenetic branching process of platyrrhines. To investigate this diversification, we used geometric morphometric techniques, a molecular phylogenetic tree, ecological data and phylogenetic comparative methods. Our statistical analyses demonstrated that the phylogenetic branching process is the most important dimension to understand cranial shape variation among extant platyrrhines and suggested that the main shape divergence among the four principal platyrrhine clades probably occurred during the initial branching process. The phylogenetic conservatism, which is the retention of ancestral traits over time within the four principal platyrrhine clades, could be the most important characteristic of platyrrhine cranial shape diversification. Different factors might have driven early shape divergence and posterior relative conservatism, including genetic drift, stabilizing selection, genetic constraints owing to pleiotropy, developmental or functional constraint, lack of genetic variation, among others. Understanding the processes driving the diversification among platyrrhines will probably require further palaeontological, phylogenetic and comparative studies.

Theoretical approaches to forensic entomology: I. Mathematical model of postfeeding larval dispersal

Abstract: An overall theoretical approach to model phenomena of interest for forensic entomology is advanced. Efforts are concentrated in identifying biological attributes at the individual, population and community of the arthropod fauna associated with decomposing human corpses and then incorporating these attributes into mathematical models. In particular in this paper a diffusion model of dispersal of postfeeding larvae is described for blowflies, which are the most common insects associated with corpses.

Population dynamics of Chrysomya putoria (Wied.) (Dipt., Calliphoridae)

The effect of larval density on fecundity and survival of Chrysomya putoria was analysed in this study to characterize the dynamics of experimental populations of this species. Estimates of fecundity and survival were incorporated into a first‐order finite difference equation, written as nt+1 = 1/2 F(nt) S (nt) nt. The dynamic behavior of this equation was assessed to deduce the nature of the population dynamics of C. putoria. Exponential functions fitted to the fecundity and survival data indicate that these traits decrease significantly as a function of increasing density of immatures. The mathematical model applied to experimental populations of C. putoria predicts a theoretical two‐point limit cycle for immatures and adults.

Larval dispersal in Chrysomya megacephala, Chrysomya putoria and Cochliomyia macellaria (Dipt., Calliphoridae) : Ecological implications of aggregation behaviour

Abstract: In this study we investigate aggregated patterns as a consequence of post‐feeding larval dispersal in three blowfly species, based on the frequency distribution of sampling units in the substrate having 0, 1, 2,…,n pupae. Statistical analysis revealed that aggregated patterns of distribution emerge as a consequence of larval dispersal, and Cochliomyia macellaria has higher levels of aggregation when compared to Chrysomya megacephala and C. putoria. Aggregation during dispersal is associated with a spatial pattern where most larvae in the species tend to pupariate near the food source. The possible consequences for the population ecology of these species are discussed.

Bootstrap Confidence Regions for Canonical Variates: Application to Studies of Evolutionary Differentiation

Theory recently developed to construct confidence regions based on the parametric bootstrap is applied to add inferential information to graphical displays of sample centroids in canonical variate analysis. Problems of morphometric differentiation among subspecies and species are addressed using numerical resampling procedures.

The spatial dynamics of native and introduced blowflies (Dipt., Calliphoridae)

The spatial dynamics of three blowfly species was investigated using a spatially extended model of density‐dependent population growth and the results indicate an overall stabilizing effect. Introduction of diffusive dispersal induced a quantitative effect of damping variation in population size on the route to a one‐fixed point equilibrium in the native species, Cochliomyia macellaria. On the other hand, diffusive dispersal caused qualitative shifts in the dynamics of two invading species, Chyrsomya megacephala and Chrysomya putoria. In both species diffusive dispersal can produce a qualitative shift from a two‐point limit cycle to a one fixed‐point dynamics. Quantitatively, dispersal also has the effect of damping oscillations in population in the invading species.

Diffusion model applied to postfeeding larval dispersal in blowflies (Diptera:Calliphoridae).

This paper presents a diffusion model of larval dispersal specifically designed to account for particular aspects of postfeeding larval dispersal from the food source in organisms such as blowflies. In these organisms the dispersal of immatures includes two groups of individuals, those that are actively migrating and those that have initiated the pupation process. The classical diffusion equation in one dimension was modified to incorporate a function which describes the burying of larvae to become pupae. The analytical solution of this equation predicts oscillatory and monotonic dispersal behaviors, which are observed in experimental populations of blowfly species.

Theoretical estimates of consumable food and probability of acquiring food in larvae of Chrysomya putoria (Diptera: Calliphoridae)

An indirect estimate of consumable food and probability of acquiring food in a blowfly species, Chrysomya putoria, is presented. This alternative procedure combines three distinct models to estimate consumable food in the context of the exploitative competition experienced by immature individuals in blowfly populations. The relevant parameters are derived from data for pupal weight and survival and estimates of density-independent larval mortality in twenty different larval densities. As part of this procedure, the probability of acquiring food per unit of time and the time taken to exhaust the food supply are also calculated. The procedure employed here may be valuable for estimations in insects whose immature stages develop inside the food substrate, where it is difficult to partial out confounding effects such as separation of faeces. This procedure also has the advantage of taking into account the population dynamics of immatures living under crowded conditions, which are particularly characteristic of blowflies and other insects as well.