Population spatial structuring on the feeding grounds in North Atlantic humpback whales (Megaptera novaeangliae)

Population spatial structuring among North Atlantic humpback whales Megaptera novaeangliae on the summer feeding grounds was investigated using movement patterns of identified individuals. We analysed the results from an intensive 2-year ocean-basin-scale investigation resulting in 1658 individuals identified by natural markings and 751 individuals by genetic markers supplemented with data from a long-term collaborative study with 3063 individuals identified by natural markings. Re-sighting distances ranged from <1 km to >2200 km. The frequencies ( F ) of re-sighting distances ( D ) observed in consecutive years were best modelled by an inverse allometric function ( F =6631 D ^−1.24, r ²=0.984), reflecting high levels of site fidelity (median re-sighting distance <40 km) with occasional long-distance movement (5% of re-sightings >550 km). The distribution of re-sighting distances differed east and west of 45°W, with more long-distance movement in the east. This difference is consistent with regional patterns of prey distribution and predictability. Four feeding aggregations were identified: the Gulf of Maine, eastern Canada, West Greenland and the eastern North Atlantic. There was an exchange rate of 0.98% between the western feeding aggregations. The prevalence of long-distance movement in the east made delineation of possible additional feeding aggregations less clear. Limited exchange between sites separated by as little as tens of kilometres produced lower-level structuring within all feeding aggregations. Regional and temporal differences in movement patterns reflected similar foraging responses to varying patterns of prey availability and predictability. A negative relationship was shown between relative abundance of herring and sand lance in the Gulf of Maine and humpback whale movement from the Gulf of Maine to eastern Canada.     

Spatial patterns, temporal variability, and the role of multi-nest colonies in a monogynous Spanish desert ant

Abstract 1. The colonies of the Spanish desert ant Cataglyphis iberica are polydomous. This study describes the temporal and spatial patterns of the polydomy in this species at two different sites, and presents analyses of its role in reducing the attacks of the queen over sexual brood, and in allowing better habitat exploitation.
2. The spatial distribution of nests was clumped while colonies were distributed randomly. Mean nearest neighbour distance ranged from 3.4 to 7.0 m for nests and from 12.3 to 14.1 m for colonies. Distance of foragers searching for food varied among nests: mean values were between 6.1 and 12.6 m.
3. At both sites, the maximum number of nests per colony occurred in summer, during the maximum activity period of the species. Colonies regrouped at the end of this period but overwintered in several nests.
4. Nest renewal in C. iberica colonies was high and showed great temporal variability: nests changed (open, close, re-open) continuously through the activity season and/or among years. The lifetime of up to 55% of nests was only 1–3 months.
5. Polydomy in C. iberica might decrease the interactions between the queen and the sexual brood. In all colonies excavated just before the mating period, the nest containing the queen did not contain any virgin female. Females were in the queenless nests of the colony.
6. The results also suggest that polydomous C. iberica colonies may enhance habitat exploitation because foraging activity per colony increases with nest number. The relationship between total prey input and foraging efficiency and number of nests per colony attains a plateau or even decreases after a certain colony size (four to six nests). This value agrees with the observed mean number of nests per colony in C. iberica .     

Structural and chemical ontogeny of the postpharyngeal gland in the desert ant Cataglyphis niger

Abstract. The postpharyngeal gland of Cataglyphis niger (André, 1881) workers is characterized, at the ultrastructural level, by a well-developed smooth endoplasmic reticulum, Golgi apparatus, and numerous mitochondria and lamellar inclusions suggesting an involvement in lipid metabolism. In addition, the microvillar differentiation of the apical membrane and basal invaginations of the cell imply a transportation process.
The gland shows a clear structural as well as chemical age-dependent development. Epithelial thickness increases with age, reaching its maximum within the first week after emergence. Concurrently there is a progressive development of microvilli and appearance of the lamellar inclusions. The gland's secretion consists mainly of hydrocarbons, with a predominance of monomethyl and dimethyl alkanes. Congruency was found between the hydrocarbon composition of glandular exudates and those of the epicuticular washes. An age-dependent increase in the total amount of hydrocarbons was found to correlate with the ultrastructural development and gross morphology (thickness of epicuticular lining) of the gland.     

Modeling hunter-gatherer decision making: complementing optimal foraging theory

While optimal foraging theory has been of considerable value for understanding hunter-gatherer subsistence patterns, there is a need for a complementary approach to human foraging behavior which focuses on decision-making processes. Having made this argument, the paper proposes the type of modeling approach that should be developed, using decision making during encounter foraging as an example. This model concerns the individual decision maker attempting to improve his foraging efficiency, rather than maximize it, under the constraint of limited information and with conflicting goals. This is illustrated by applying it to the Valley Bisa hunters using computer simulation.     

Diet-shifts by an estuarine goby (Pomatoschistus microps) in the face of variable prey availability

Ontogenetic shifts in diet provide a mechanism for maximising fitness throughout development and are common where predators exhibit large increases in size. In order to maximise their fitness throughout development, benthic feeding fish can show diet-shifts that centre on the transition from meiofaunal to macrofaunal prey. Here we assessed whether such a shift was influenced by natural variation in prey-size availability by comparing the sizes of prey consumed by naturally foraging common gobies (Pomatoschistus microps). We tested explicitly for the presence of an ontogenetic shift by analysing the length of prey consumed and an index for prey importance for gobies of different lengths. We also tested the match between actual diets and those predicted by a foraging model. The goby size at which the diet-shift occurred was consistent among locations that differed in their availability of prey and through temporal changes in densities and types of prey. The mean sizes of ingested prey increased for gobies > 35 mm in length and the relative importance of macrofauna increased at 30 mm. The foraging model predicted that gobies > 30 mm would eat larger prey than would smaller gobies which differed from the observed changes in prey-size at 35 mm. Availability of prey did not appear to influence the lengths at which gobies changed diet but did affect the size of prey taken after the diet-shift. A relatively large abundance of large-bodied chironomids at two sites was reflected in the mean size of prey consumed by gobies > 30 mm at these sites. Our study indicates that intrinsic mechanisms can be more important than fluctuating environments in determining prey-choice and shifts in diet, although for the common goby, variability in prey-size may have implications for prey-choice later in ontogeny.     

Saltatory Search in Free-Living <Emphasis Type=Italic>Callithrix jacchus</Emphasis>: Environmental and Age Influences

Researchers generally categorize motile foraging behavior into 3 strategies: ambush, cruise, and saltatory searching. During saltatory searches, predators move from one location to the next, frequently pausing to scan for prey that are hard to detect and widely distributed. We investigated whether 1) the foraging strategy of free-living common marmosets conforms to the strategy; 2) scanning occurs solely when the individual is stationary; 3) the environment (dense and sparse vegetation) influences foraging behavior; and 4) the age of the marmosets is related to their foraging behavior. Bezerra carried out the observations in a 32-ha fragment of Atlantic Forest in the Northeast of Brazil and in an adjacent condominium. Using the focal sampling method, we observed 31 common marmosets, including adults, juveniles, and infants, Bezerra recorded the following behaviors (in dense and sparse vegetation): locomotion (subdivided into minor locomotion—moving distances ≤1 m; major locomotion—moving distances >1 m), scan, pause, and capture. The frequency of scanning behavior was significantly greater when individuals were stationary. Adults and juveniles exhibited the clearest differentiation in terms of locomotion, both adjusting the behavior in accordance with the environment; periods of major locomotion were more frequent in sparse vegetation, whereas minor locomotion was more frequent in dense vegetation. In contrast, infants exhibited major locomotion more frequently in dense vegetation. We conclude that common marmosets use a saltatory strategy when foraging, and that their foraging behavior is plastic, changing both with the age of the individual and with the density of the vegetation.     

Blue tail and striped body: why do lizards change their infant costume when growing up?

Ontogenetic changes in color and pattern that are not directlyrelated to reproduction are very common yet remain a poorlyunderstood phenomenon. One example is conspicuous colors inthe tails of fish, amphibians, and reptiles that fade out laterin life. We suggest a novel hypothesis: conspicuous tail colorsthat appear only in juveniles compensate for an increased activitylevel, deflecting imminent attacks to the tail. We observedblue-tailed, newly hatched lizards (Acanthodactylus beershebensis)in the field and compared 5 behavioral parameters with thoseof older individuals that had already lost their neonate coloration.In addition, we explored whether tail displays, often assumedto direct a predator's attention to the tail, disappear withthe color change. Striped blue-tailed hatchlings foraged moreactively than 3-week-old juveniles, spent a longer time in openmicrohabitats, and performed deflective tail displays. In comparison,2 other lacertids that do not undergo ontogenetic change didnot switch to safer foraging when growing up. The results suggestthat activity alteration may be a major factor affecting theontogenetic color and pattern change. Active lizards that foragein open habitats increase their probability of attack by ambushpredators. Conspicuous colors and deflection displays may shiftattacks to the expendable tail, increasing the prey's overallprobability of surviving attacks. The persistence of both stripedbody pattern and blue tail fits the active foraging period ofneonates and hence may be appropriate for other species thatdisplay a conspicuous tail accompanied by a striped pattern.     

Individual variation in the ability of Columbian ground squirrels to select an optimal diet

Summary Columbian ground squirrels (Spermophilus columbianus) were examined for ability to select a diet that maximizes daily energy intake (optimal diet) under free-living field conditions. The optimal diet for each squirrel was determined given constraints (e.g. body size, feeding time) on individual foraging behavior. Most squirrels (63%) consumed a diet not significantly different from one that would maximize their daily energy intake. The remainder (37%) approached an energy maximized diet but appeared to make some incorrect foraging decisions. Both males and females appeared to approach energy maximized diets. An individual's deviation from its optimal diet is relatively constant within a season and not significantly affected by immediate environmental influences such as food abundance, thermal conditions and social environment. The energy cost of deviating from an optimal diet may be large enough to affect fitness. These results suggest that the ability to select an optimal diet can be viewed as a behavioral trait that might be subject to natural selection.     

A Comparison of Foraging Behavior in Two “Percher” Dragonflies, Pachydiplax longipennis and Erythemis simplicicollis (Odonata: Libellulidae)

Feeding behaviors of two adult libellulid percher dragonflies, Pachydiplax longipennis and Erythemis simplicicollis, were compared. All results pertain to feeding from natural perches located some distance away from reproductive rendezvous sites. Compared to P. longipennis, E. simplicicollis chose broader and less structurally discrete perches, moved more frequently and over a larger area, and took, on average, much larger prey, although diet overlapped broadly in the two species. Erythemis made more frequent feeding flights but with a much lower success rate than Pachydiplax; consequently the prey capture rate was similar in the two species. Gut contents of mature, but not of immature, E. simplicicollis comprised a significantly greater proportion of body mass than in P. longipennis, apparently confirming the importance of larger prey in the diet of the former.     

Pollen foraging behaviour of solitary Hawaiian bees revealed through molecular pollen analysis

Obtaining quantitative information concerning pollinator behaviour has become a primary objective of pollination studies, but methodological limitations hinder progress towards this goal. Here, we use molecular genetic methods in an ecological context to demonstrate that endemic Hawaiian Hylaeus bees (Hymenoptera: Colletidae) selectively collect pollen from native plant species in Haleakala and Hawaii Volcanoes National Parks. We identified pollen DNA from the crops (internal storage organs) of 21 Hylaeus specimens stored in ethanol for up to 3 years. Genetic analyses reveal high fidelity in pollen foraging despite the availability of pollen from multiple plant species present at each study site. At high elevations in Haleakala, pollen was available from more than 12 species of flowering plants, but Hawaiian silversword (Argyroxiphium sandwicense subsp. macrocephalum) comprised 86% of all pollen samples removed from bee crops. At lower elevations in both parks, we only detected pukiawe (Leptecophylla (Styphelia) tameiameiae) pollen in Hylaeus crops despite the presence of other plant species in flower during our study. Furthermore, 100% of Hylaeus crops from which we successfully identified pollen contained native plant pollen. The molecular approaches developed in this study provide species-level information about floral visitation of Hawaiian Hylaeus that does not require specialized palynological expertise needed for high-throughput visual pollen identification. Building upon this approach, future studies can thus develop appropriate and customized criteria for assessing mixed pollen loads from a broader range of sources and from other global regions.     

The allocation of foragers in red wood ants

Abstract. 1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers.
2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest.
3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source.
4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails.
5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.