We study the role of dynamical constraints in the general problem of finding the best statistical strategy for random searching when the targets can be detected only in the limited vicinity of the searcher. We find that the optimal search strategy depends strongly on the delay time tau during which a previously visited site becomes unavailable. We also find that the optimal search strategy is always described for large step lengths l by a power-law distribution P(l) approximately l(-mu), with 1

We study through a reaction-diffusion algorithm the influence of landscape diversity on the efficiency of search dynamics. Remarkably, the identical optimal search strategy arises in a wide variety of environments, provided the target density is sparse and the searcher’s information is restricted to its close vicinity. Our results strongly impact the current debate on the emergentist vs. evolutionary origins of animal foraging. The inherent character of the optimal solution (i.e., independent on the landscape for the broad scenarios assumed here) suggests an interpretation favoring the evolutionary view, as originally implied by the Lévy flight foraging hypothesis. The latter states that, under conditions of scarcity of information and sparse resources, some organisms must have evolved to exploit optimal strategies characterized by heavy-tailed truncated power-law distributions of move lengths. These results strongly suggest that Lévy strategies—and hence the selection pressure for the relevant adaptations—are robust with respect to large changes in habitat. In contrast, the usual emergentist explanation seems not able to explain how very similar Lévy walks can emerge from all the distinct non-Lévy foraging strategies that are needed for the observed large variety of specific environments. We also report that deviations from Lévy can take place in plentiful ecosystems, where locomotion truncation is very frequent due to high encounter rates. So, in this case normal diffusion strategies—performing as effectively as the optimal one—can naturally emerge from Lévy. Our results constitute the strongest theoretical evidence to date supporting the evolutionary origins of experimentally observed Lévy walks.

One of the most important aspects in the general search problem of finding randomly located target sites concerns how to characterize the role played by the non-revisitability delay time τ during which a previously found target becomes unavailable to the searcher. By using an appropriate parameterization of the number of random walk steps undertaken between successive targets, we show that for the case of sparse randomly distributed sites the optimal search strategy shifts from a superdiffusive to a ballistic strategy consisting of essentially rectilinear motion between the targets, as τ increases from τ → 0t oτ →∞ , respectively. The crossover between these limiting regimes occurs as a function of τ. These conclusions are shown to hold even if dissipative phenomena are considered in the searching dynamics. We discuss the results in the context of their application to animal foraging. Recently, much progress has been achieved [1-4] in solving the general random search problem (RSP), i.e., adapting the best statistical strategy for finding randomly located revisitable or non-revisitable targets sites that can only be detected in the limited vicinity of the searcher. Besides the applications in distinct areas as technology [5] and ecology [1, 6-8], the RSP has a deep connection with a classic problem in physics [9,10]: how the root-mean-square displacement scales with the number of steps of a random walker and how it leads to diffusive and superdiffusive behavior [11-14]. Such a connection becomes clear by observing that the mean number of flights taken by the searcher while traveling between two successive target sites, N s , appears explicitly in the random search statistical efficiency η =1/(ℓ N s), which is the function to be optimized [2]. ℓ is the mean flight distance traveled in each flight step. A key aspect in the RSP relates to determining how the best strategy varies with respect to the delay time τ during which a target site just found becomes unavailable to subsequent visits [15]. The importance of this question can be appreciated, for instance, by mentioning that in the context of animal foraging [1-4, 6-8] such a non-revisitability time is quite an important parameter and emerges due to the fact that, in Nature, realistic targets cannot be

Habitat loss and fragmentation are important factors determining animal population dynamics and spatial distribution. Such landscape changes can lead to the deleterious impact of a significant drop in the number of species, caused by critically reduced survival rates for organisms. In order to obtain a deeper understanding of the threeway interplay between habitat loss, fragmentation and survival rates, we propose here a spatially explicit multi-scaled movement model of individuals that search for habitat. By considering basic ecological processes, such as predation, starvation (outside the habitat area), and competition, together with dispersal movement as a link among habitat areas, we show that a higher survival rate is achieved in instances with a lower number of patches of larger areas. Our results demonstrate how movement may counterbalance the effects of habitat loss and fragmentation in altered landscapes. In particular, they have important implications for conservation planning and ecosystem management, including the design of specific features of conservation areas in order to enhance landscape connectivity and population viability.

Observations on group size and composition of marine tucuxi dolphins, Sotalia guianensis, found in the Cananéia estuary (25 o 03'S, 47 o 55'W), southeastern Brazil, were conducted from May 2000 to July 2003. Correlations among four environmental variables (water temperature, salinity, transparency and depth) and group size were investigated, as well as on the way foraging and feeding behavioral patterns related to group formation in S. guianensis. The surveyed area comprised approximately 132km 2 and field efforts were conducted in 87 days. A total of 378 groups were recorded. Group size (mean ± SD: 12.4 ± 11.4 individuals) varied from lone individuals, rarely seen, to aggregations of up to 60 individuals. No significant differences were found regarding group size among seasons. Groups with calves (89.7% of all observed groups) were more frequent than groups without calves. Feeding associations with marine birds were common in winter when waters were clearer. A positive correlation was only reported when investigating group size and water depth (Spearman's rank test, r=0.4716, p=0.0000). Marine tucuxis usually form large aggregations (20 to 60 individuals) when engaged in feeding activities in deeper waters. Groups were larger (mean ± SD: 18.3 ± 15.0 individuals, n=90) in the main estuary entrance, where water is deeper, and smaller in inland shallower waters (mean ± SD: 7.8 ± 6.9 individuals, n=47). Because of these common observed aggregations, this area of the estuary has been used as a dolphin watching site since the late 1990s without specific regulations. Guidelines are urgently needed to conduct dolphin watching tours as calves are seen year-round and uncontrolled tourism may disrupt important social interactions. RESUMO:Observações a respeito do tamanho e da composição de grupos do boto-tucuxi marinho, Sotalia guianensis, encontrados no estuário de Cananéia (25 o 03'S, 47 o 55'W), sudeste do Brasil, foram conduzidas entre os meses de maio de 2000 a julho de 2003. Correlações entre quatro variáveis ambientais (temperatura, salinidade, transparência, e profundidade da água) e tamanho de grupos foram investigadas, assim como sobre a forma com que padrões comportamentais relacionados à alimentação poderiam estar relacionados com a formação de grupos em S. guianensis. A área de estudo apresentou aproximadamente 132km 2 e os esforços de campo foram desenvolvidos em 87 dias de investigações. Um total de 378 grupos foi observado. Os tamanhos de grupo (média ± DP: 12,4 ± 11,4 indivíduos) variaram entre indivíduos solitários raramente observados a agregações de até 60 indivíduos. Não foram detectadas diferenças significativas relacionadas aos tamanhos de grupos observados em diferentes estações do ano. Grupos contendo filhotes (89,7% de todos os grupos observados) foram mais freqüentes do que os grupos sem filhotes. Associações alimentares com aves marinhas foram comuns no inverno quando as águas são mais claras. Uma correlação positiva foi apenas reportada quando da investigação do tamanho de grupo relacionado à p...