Ethanol concentration in food and body condition affect foraging behavior in Egyptian fruit bats (Rousettus aegyptiacus)

Ethanol occurs in fleshy fruit as a result of sugar fermentation by both microorganisms and the plant itself; its concentration [EtOH] increases as fruit ripens. At low concentrations, ethanol is a nutrient, whereas at high concentrations, it is toxic. We hypothesized that the effects of ethanol on the foraging behavior of frugivorous vertebrates depend on its concentration in food and the body condition of the forager. We predicted that ethanol stimulates food consumption when its concentration is similar to that found in ripe fruit, whereas [EtOH] below or above that of ripe fruit has either no effect, or else deters foragers, respectively. Moreover, we expected that the amount of food ingested on a particular day of feeding influences the toxic effects of ethanol on a forager, and consequently shapes its feeding decisions on the following day. We therefore predicted that for a food-restricted forager, ethanol-rich food is of lower value than ethanol-free food. We used Egyptian fruit bats (Rousettus aegyptiacus) as a model to test our hypotheses, and found that ethanol did not increase the value of food for the bats. High [EtOH] reduced the value of food for well-fed bats. However, for food-restricted bats, there was no difference between the value of ethanol-rich and ethanol-free food. Thus, microorganisms, via their production of ethanol, may affect the patterns of feeding of seed-dispersing frugivores. However, these patterns could be modified by the body condition of the animals because they might trade-off the costs of intoxication against the value of nutrients acquired.     

Local knowledge and training towards management

The urgency of managing marine resources is based on the fact that half of the world stocks are fully exploited, excluding those stocks that are already depleted. Artisanal fisheries in Brazil, both inland and coastal, are responsible for about half of the country’s catches. Therefore, management of local artisanal fisheries is a necessity that provides an additional benefit, considering the observation that decentralization and the use of local ecological knowledge (LEK) in management have given better results than centralized, top-down management. In this study, a third system of knowledge–based on practice and training–is built from the local and scientific systems of knowledge, and a method to accomplish practical steps in local management is shown. Four elements are considered for the process of linking systems towards management: (1) an understanding of the natural environment of the fishery and on the use of natural resources by locals; (2) the knowledge of the marine area used by fishers, i.e., location of fishing spots for each species; (3) the understanding of fisher behavior, e.g., using tools from optimal foraging theory; and (4) the knowledge fishers have of the biology and ecology of species and their LEK, based on studies of the ethnobiology, ethnoecology, and ethnotaxonomy of fish. Considering the availability of publications on topics 1 and 2, illustrative cases are shown using optimal foraging models in Itaipu Beach, Rio de Janeiro and São Paulo Bagre, Cananéia, São Paulo, and using common snook, Centropomus undecimalis, as an example for a target species. Finally, local programs including training courses using both scientific and local knowledge are proposed within coastal artisanal fisheries.     

Vigilance behaviour and fitness consequences: comparing a solitary foraging and an obligate group-foraging mammal

Vigilance behaviour in gregarious species has been studied extensively, especially the relationship between individual vigilance and group size, which is often negative. Relatively little is known about the effect of conspecifics on vigilance in non-obligate social species or the influence of sociality itself on antipredator tactics. We investigated predator avoidance behaviour in the yellow mongoose, Cynictis penicillata, a group-living solitary forager, and compared it with a sympatric group-living, group-foraging herpestid, the meerkat, Suricata suricatta. In yellow mongooses, the presence of conspecifics during foraging—an infrequent occurrence—reduced their foraging time and success and increased individual vigilance, contrary to the classical group-size effect. Comparing the two herpestids, sociality did not appear to affect overt vigilance or survival rates but influenced general patterns of predator avoidance. Whereas meerkats relied on communal vigilance, costly vigilance postures, and auditory warnings against danger, yellow mongooses avoided predator detection by remaining close to safe refuges and increasing “low-cost” vigilance, which did not interfere with foraging. We suggest that foraging group size in herpestids is constrained by species-distinct vigilance patterns, in addition to habitat and prey preference.     

Creation and preservation of vegetation patterns by grazing

Structural patterns of tall stands (“tussock”) and short stands (“lawn”) are observed in grazed vegetation throughout the world. Such structural vegetation diversity influences plant and animal diversity. A possible mechanism for the creation and preservation of such patterns is a positive feedback between grazing and plant palatability. Although some theoretical studies have addressed this point in a non-spatial setting, the spatial consequences of this feedback mechanism on the stability and spatial characteristics of vegetation structure patterns have not been studied.We addressed this issue by analyzing a spatially explicit individual-based plant-grazer simulation model, based on published empirical relations and the assumption of optimal foraging.In the model, the selection by the grazer of short stands (that have a higher energy content and are more palatable) is affected by traveling costs and the spatial organization of swards. Nevertheless, the most selected biomass in this type of short stands was the optimal biomass predicted by cropping and digestion constraints. As a result of the optimal foraging strategy, the grazers displayed Lévy-flight traveling behavior during the simulations with characteristic exponent μ ≈ 2.Patterns of short and tall stands created by grazing were preserved for at least a decade. Even in seasonal habitat, the spatial organization of the patterns remained relatively constant, despite fluctuations in the area of short stands. Heterogeneity of initial vegetation increased heterogeneity of the grazing-induced pattern, but did not affect its stability.The area of short stands that was preserved by grazing scaled with the herbivore mass to the power 0.4 and with the carrying capacity of the vegetation to the power −0.75.Patterns of tall and short stands can be created and perpetuated by optimally grazing ruminants, irrespective of possible underlying soil patterns. The simulations generate predictions for the stability and spatial characteristics of such structural vegetation patterns.     

Combined use of pheromone trails and visual landmarks by the common garden ant Lasius niger

This study investigated the relative importance of pheromone trails and visual landmarks on the ability of Lasius niger foragers to relocate a previously used food source. Colonies formed foraging trails to a 1-M sucrose feeder. Sections of this trail were then presented back to the same colony after variable time intervals. Individual outgoing foragers were observed to determine if they walked for 15 cm in the direction of the feeder or not. On newly established pheromone trails formed by 500 ant passages, 77% of the foragers walked in the correct direction vs 31% for control foragers (no trail pheromone). Pheromone trails decayed to the control levels in 20–24 h. Trails formed with fewer ant passages (125 or 30) decayed quicker. The use of visual landmarks was investigated by using trails with outgoing foragers from the colony that established the trail, either in the same room or in a different room, with different visual landmarks, to that used during trail establishment. Approximately 20% more ants walked in the correct direction in the same room vs the different room. This difference decreased to around 10% 2 h after trail establishment, indicating that the ants in the different room were learning the new visual cues to navigate by. Our results show that visual landmarks and pheromone trails are approximately equally useful in initially guiding L. niger foragers to food locations and that these two information sources have a complementary function.     

The effect of dominance hierarchy on the use of alternative foraging tactics: a phenotype-limited producing-scrounging game

Group living is thought to be advantageous for animals, though it also creates opportunities for exploitation. Using food discovered by others can be described as a producer-scrounger, frequency-dependent game. In the game, scroungers (parasitic individuals) do better than producers (food finders) when scroungers are rare in the group, but they do worse when scroungers are common. When the individuals' payoffs do not depend on their phenotype (i.e. a symmetric game), this strong negative frequency dependence leads to a mixed stable solution where both alternatives obtain equal payoffs. Here, we address the question of how differences in social status in a dominance hierarchy influence the individuals' decision to play producer or scrounger in small foraging groups. We model explicitly the food intake rate of each individual in a dominance-structured foraging group, then calculate the Nash equilibrium for them. Our model predicts that only strong differences in competitive ability will influence the use of producing or scrounging tactics in small foraging groups; dominants will mainly play scrounger and subordinates will mostly use producer. Since the differences in competitive ability of different-ranking individuals likely depend on the economic defendability of food, our model provides a step towards the integration of social foraging and resource defence theories. Received: 30 July 1997 / Accepted after revision: 15 November 1997     

Body mass and parental decisions in the Antarctic petrel Thalassoica antarctica : how long should the parents guard the chick?

In Procellariiformes, the parents guard the chick after it has attained homeothermy. This strategy may reduce the probability that a small chick is taken by predators, but is costly as only one parent can forage at a time. The decision to leave the chick may therefore be a compromise between the chick's vulnerability to predators, the body condition of the parent on the nest and whether the foraging parent returns in time. We studied how the number of days that parents guarded the chick was related to the body mass of the parent at the nest and the time the foraging parent spent at sea in the Antarctic petrel Thalassoica antarctica. We also examined how the body mass of the parent on the nest and the duration of the foraging trips influenced the chicks' body condition at the end of the guarding period. When the foraging parent did not return to the nest in time to relieve its mate, the number of days the parent on the nest kept guarding the chick was positively related to its body mass on arrival in the colony. The number of days the foraging parent spent at sea was positively related to the body mass of its mate, but those that returned in time had a shorter stay at sea relative to their mate's body mass than those that did not return before their mate had left. Apparently, both the body mass of the parent at the nest and the ability of the foraging parent to adjust its stay at sea to the mate's body mass is important for the number of days the parents guard the chick and also the chick's body condition at this point. The inability to return to the nest before the mate has left may be the result of needing a minimum amount of time at sea to find food, or because some parents having low foraging success and therefore prolong their stay at sea. Received: 10 October 1997 / Accepted after revision: 14 March 1998     

Atmospheric NH3 as plant nutrient: a case study with Brassica oleracea

Nutrient-sufficient and nitrate- or sulfate-deprived plants of Brassica oleracea L. were exposed to 4 microl l(-1) NH3 (2.8 mg m(-3)), and effects on biomass production and allocation, N-compounds and root morphology investigated. Nitrate-deprived plants were able to transfer to atmospheric NH3 as nitrogen source, but biomass allocation in favor of the root was not changed by exposure to NH3. NH3 reduced the difference in total root length between nitrate-sufficient and nitrate-deprived plants, and increased the specific root length in the latter. The internal N status, therefore, might be involved in controlling root length in B. oleracea. Root surface area, volume and diameter were unaffected by both nitrate deprivation and NH3 exposure. In sulfate-deprived plants an inhibitory effect of NH3 on root morphological parameters was observed. These plants, therefore, might be more susceptible to atmospheric NH3 than nitrate-deprived plants. The relevance of the present data under field conditions is discussed.     

Social foraging in stingless bees: how colonies of Melipona fasciata choose among nectar sources

In an experimental set-up, a colony of the stingless bee Melipona fasciata demonstrated its ability to choose the better of two nectar sources. This colony pattern was a result of the following individual behavioural decisions: continue foraging, abandon the feeder, restart foraging and initiate foraging. Only very rarely did individuals switch from one feeder to the other. With the first combination of a rich (2.7 M) and a poor (0.8 M) feeder M. fasciata behaved differently from Apis mellifera. Recruitment occurred to both feeders and the poor feeder was not abandoned completely. When the poor feeder was set to 0.4 M, M. fasciata abandoned the poor feeder rapidly and allocated more foragers to the rich feeder. These patterns were similar to those reported for A. mellifera with the first combination of feeders. Over a sequence of 4 days, experienced bees increasingly determined the colony patterns, and the major function of communication between workers became the reactivation of experienced foragers. The foragers modulated their behaviour not only according to the profitability of the feeder, but also according to previous experience with profitability switches. Thus, experience and communication together regulated colony foraging behaviour. These findings and the results of studies with honeybees suggest that M. fasciata and honeybees use similar decision-making mechanisms and only partly different tools. Received: 21 December 1998 / Accepted: 5 January 1999     

The Value of Rehabilitating Logged Rainforest for Birds

Abstract: The recent advent of carbon crediting has led to a rapid rise in biosequestration projects that seek to remove carbon from the atmosphere through afforestation and forest rehabilitation. Such projects also present an important potential opportunity to reverse biodiversity losses resulting from deforestation and forest degradation, but the biodiversity benefits of different forms of biosequestration have not been considered adequately. We captured birds in mist nets to examine the effects of rehabilitation of logged forest on birds in Sabah, Borneo, and to test the hypothesis that rehabilitation restores avian assemblages within regenerating forest to a condition closer to that seen in unlogged forest. Species richness and diversity were similar in unlogged and rehabilitated forest, but significantly lower in naturally regenerating forest. Rehabilitation resulted in a relatively rapid recovery of populations of insectivores within logged forest, especially those species that forage by sallying, but had a marked adverse effect on frugivores and possibly reduced the overall abundance of birds within regenerating forest. In view of these results, we advocate increased management for heterogeneity within rehabilitated forests, but we strongly urge an increased role for forest rehabilitation in the design and implementation of a biodiversity‐friendly carbon‐offsetting market.