El Niño events,the lean versus fat scenario,and long‐term guild dynamics of vertebrate predators in a South American semiarid ecosystem

Abstract Predator assemblages are complex systems in which asynchrony in the dynamics of resources and consumers, and the idiosyncratic perception of environmental conditions by the predators may obscure the detection of expected patterns. We disentangle the specific effects of these variables on the guild structure of a vertebrate predatory assemblage in a semiarid ecosystem of western South America. Over 16 years, this system faced dramatic fluctuations in prey availability associated with four El Niño events. After controlling for other sources of variation, we tested if increased resource availability is associated with higher niche overlaps, as expected from the lean/fat scenario. We determined the existence of two trophic guilds of predators (specialized mammal‐eaters and omnivorous species with emphasis on arthropods) and found that they responded to increased productivity both at the guild and whole assemblage levels. However, the population response of arthropod prey (almost simultaneous) and of different small mammal prey (delayed by 1 or 2 years) to productivity imposed a degree of asynchrony in prey availability and in the response of predators. This resulted in the between‐guilds exchange of predator species depending on mammal prey scarcity or abundance. As a consequence, the observed pattern was an apparent lack of response at the assemblage level. Despite differences in the perception of prey levels by predators, we conclude that each one of them responded accordingly to theoretical predictions following a simple rule: if prey resources are not limiting, predators behave opportunistically converging over the most abundant resources, thus increasing niche overlap; if prey shortages occur, predators specialize on those prey resources that they gather most efficiently, thus lowering niche overlap; if resources become even scarcer, all predators converge again upon the few prey resources still available, thus increasing overlap – out of necessity.     

A partial food web involving predatory gastropods on a Pacific fringing reef

An analysis of the feeding habits of a diverse assemblage of predatory gastropods on a Guam fringing reef, shows that seven major prey categories are eaten, namely polychaetes, sipunculans, gastropods, bivalves, crustaceans, ophiuroids, and fish. The three largest feeding groups are the polychaete feeding guild which mainly consists of species of Conus, the gastropod guild dominated by species of the Muricidae and the sipunculan guild consisting mainly of the Mitridae. There is considerable dietary overlap between members of feeding guilds, but interaction between guilds is low and accounted for by the relatively few generalist species in the community.     

Food habits of small fishes in a common reed <Emphasis Type="Italic">Phragmites australis</Emphasis> belt in Lake Shinji,Shimane, Japan

To clarify the feeding habits of reed fishes, the gut contents of 13 fish species collected in a Phragmites australis belt in Lake Shinji were examined. Six species showed ontogenetic and/or seasonal changes in food use patterns. Smaller individuals generally preyed on small planktonic items (e.g., calanoid and cyclopoid copepods) or small crustaceans (gammaridean amphipods), subsequently changing to other prey items (e.g., mysids and filamentous algae) with growth. The most important dietary items for the reed fish assemblage comprised planktonic copepods, gammaridean amphipods and mysids. However, the relative importance of these changed seasonally, gammaridean amphipods being the most important in autumn and winter, and planktonic copepods and mysids the most important in spring and in summer. Cluster analysis based on dietary overlaps showed that the reed fish assemblage comprised five feeding guilds (planktonic-copepod, mysid, gammaridean-amphipod, filamentous-algae, and detritus feeders). Of these, the three former guilds were the most abundantly represented, whereas detritivores were represented by a single species.     

A comparative analysis of food-niche relationships and trophic guild structure in two assemblages of vertebrate predators differing in species richness: causes,correlations, and consequences

Summary We conducted a comparative analysis of foodniche relationships and trophic guild structure in two assemblages of vertebrate predators (including hawks, owls, snakes, and carnivores) living in similar habitats of Chile and Spain, which differed in species richness (11 and 25 predator species, respectively), to explore how the structure of predator assemblages reflects an increase (or decrease) in the number of coexisting species. Our results indicate that the Spanish assemblage appears enriched by the symmetrical addition of species with disparately large and small values of body weight, diet breadth, and mean prey size, around the same median value found in Chile. Or, alternatively, the Chilean assemblage appears impoverished by the symmetrical loss of peripheral species — those at both tails of the frequency distribution of the above trophic estimators. Spanish predators overlap less extensively among themselves, and with smaller variance, than Chilean predators. Consequently, the higher predator richness in Spain is not ascribable to their narrower diet breadths or more extensive diet overlaps as predicted by some theoretical models. Instead, it is associated with a more spread-out use of the available resources. Trophic guilds can be recognized in the two countries, but in Spain guilds are less tightly packed. Some taxomically unrelated species are close diet analogues between Spain and Chile, whereas some closely related species cannot be matched well between countries. Circumstantial evidence suggests that the presence of some trophic guilds and of some specialist predators in either country is based on the high abundance attained by some particular prey types.     

Food habits of fishes in azostera marina bed at aburatsubo, central japan

To clarify the feeding habits of seagrass fishes, the gut contents of 31 fish species collected in aZostera marina bed at Aburatsubo central Japan, were examined. Ontogenetic changes in food preference were recognized in 12 species. In general, juveniles of the latter preyed mainly on small crustaceans (e.g., gammaridean amphipods) or planktonic animals (e.g., calanoid and cyclopoid copepods), subsequently changing to other prey items (e.g., hard-shelled animals) with growth. Cluster analysis based on dietary overlaps showed that the seagrass fish assemblage comprised seven feeding guilds (small-crustacean, planktonic-animal, large-crustacean, polychaete, fish, hard-shelled mollusc and detritus feeders). Of these, small-crustacean feeders and planktonic-animal feeders were the most abundantly represented, including juveniles of several species, which, when adult, transferred to other feeding guilds. On the other hand detritivores were represented by a single species.     

Diets and trophic‐guild structure of a diverse fish assemblage in Chesapeake Bay,U.S.A.

Dietary habits and trophic‐guild structure were examined in a fish assemblage (47 species) of the Chesapeake Bay estuary, U.S.A., using 10 years of data from >25 000 fish stomachs. The assemblage was comprised of 10 statistically significant trophic guilds that were principally differentiated by the relative amounts of Mysida, Bivalvia, Polychaeta, Teleostei and other Crustacea in the diets. These guilds were broadly aggregated into five trophic categories: piscivores, zooplanktivores, benthivores, crustacivores and miscellaneous consumers. Food web structure was largely dictated by gradients in habitat (benthic to pelagic) and prey size. Size classes within piscivorous species were more likely to be classified into different guilds, reflecting stronger dietary changes through ontogeny relative to benthivores and other guilds. Relative to predator species and predator size, the month of sampling had negligible effects on dietary differences within the assemblage. A majority of sampled fishes derived most of their nutrition from non‐pelagic prey sources, suggesting a strong coupling of fish production to benthic and demersal food resources. Mysida (predominantly the opossum shrimp Neomysis americana) contributed substantially to the diets of over 25% of the sampled predator groups, indicating that this species is a critical, but underappreciated, node in the Chesapeake Bay food web.     

Factors affecting species number and density of dabbling duck guilds in North Europe

We addressed how species number and pair density in guilds of co-existing species is related to habitat structure, and to the abundance and diversity of food resources using the assemblage of seven species of dabbling ducks (genus Anas ) breeding in 60 lakes distributed over six regions in temperate north Europe
Partial correlation and multiple regression revealed that species richness was best predicted by habitat structural diversity as indexed by a principal component analysis based on 18 vegetation and lake characteristics, and by the abundance of aquatic and emergent prey We found no effect of lake size or prey size diversity on species richness Pair density was correlated with the percentage of shoreline with horsetails ( Equisetum ), by habitat structural diversity and by the abundance of emergent invertebrate prey Neither prey size diversity nor abundance of aquatic prey correlated with pair density Species richness and pair density in North European duck guilds vary both with habitat structure and prey availability     

Patterns of morphological traits shaping the feeding guilds in the intertidal mudflat fishes of the Indian Sundarbans

Broad-scale patterns of resource utilization and the corresponding morphological evolution is a result of an integral relationship among form and function. In addition, there is also an inherent role of the latter in determining species co-interaction and assemblage pattern that forms an integral aspect of ecological research. The present study aimed to evaluate the ecomorphological relationship among 37 fish species inhabiting the intertidal mudflats of the Indian Sundarbans by outlining the following objectives: (i) identifying and characterizing feeding guilds/groups and (ii) understanding the inter-relationship between morphometry with (a) the established feeding guild classifications and (b) observed prey taxa (that characterizes these feeding groups) for determining the role of morphometry in prey acquisition followed by (iii) the evaluation of their potential phylogenetic convergence among the species. For the first objective, two approaches for feeding guild classification were made (3-Guild and 8-Guild) for assessing the prediction accuracy of morphological characters in identifying the different guilds. While the former was based on troph values, the latter classification mode relied on the similarities in diet composition among the different fish species. For addressing the second objective, we employed two different models namely, linear discriminant (LDA) and redundancy analysis (RDA). While the LDA model tested the prediction accuracy of morphological traits in classifying the different feeding guilds, RDA was applied to model the correlation between the morphological traits and the prey categories. In the LDA model, morphological characters showed higher accuracy (78.4%) in classifying three feeding groups rather than eight feeding groups (73%). Following this, the RDA model (explaining 79.78% of constrained variance) showed gill raker intensity, protrusion length, head depth, caudal peduncle, eye diameter and inter-orbital distance to be highly associated with selection of specific prey types by species, thereby characterizing a particular feeding guild. However, generalized linear models testing for correlation between troph value and feeding groups showed substantial variation (90.35%) in the dietary index being explained by the 8-Guild classification. Hence, our study maintains the assumption that broad morphological differentiation acts as one of the underlying processes resulting in dietary variations that results in the varying modes of resource utilization by the coexisting species, thereby determining the structure of a trophic guild. Furthermore, it also suggests that in terms of prey abundance or selectivity, the 8-Guild model is much more conducive in representing the feeding habits of the species while the morphological traits reflected a relatively broader scheme of classification, (i.e., 3-Guild model) with certain traits being phylogenetically conserved within these groups.     

Fish feeding guilds in shallow rocky and soft bottom areas on the Swedish west coast

Multivariate analyses of the diet relationships within fish assemblages resulted in the recognition of five major feeding guilds in shallow (0-9 m) rocky- and soft-bottom habitats on the Swedish west coast. The two habitats had similar guilds that could be broadly described as piscivores, decapod feeders, copepod feeders and amphipod and mollusc feeders. The last guild on the rocky bottom was more strictly one of amphipod feeders, whereas the last guild on soft bottoms consisted of infauna feeders (mainly polychaetes and bivalves). A comparison of the diet of the entire fish assemblages showed that amphipods and gastropods were more prevalent as prey taxa on rocky bottoms, whereas bivalves and teleosts were more common on soft bottoms. A large proportion (12 out of 27 species) of the fish species investigated was found in both habitats. These fish species generally seemed to rely on the same major prey groups in the two habitats, but also included prey taxa characteristic for the habitat in which they resided. Sea trout Salmo trutta , mackerel Scombrus scombrus , saithe Pollachius virens , whiting Merlangius merlangus and cod Gadus morhua were found to be the major piscivores in both the investigated habitats. Herring Clupea harengus and members of the family gobiidae were the most prevalent prey species for piscivores within the rocky- as well as the soft-bottom fish assemblage. A comparison of feeding modes suggested that the fish assemblage on rocky bottoms predominantly (60% of the food items) relied on food found in vegetation. On soft bottoms, the average distribution of food categories among fish species was 44% benthic, 35% pelagic and 21% vegetation-associated food items.     

Partitioning seasonal time: interactions among size, foraging activity and diet in leaf-litter frogs

This study investigates hypotheses about partitioning of food resources among all species and several size classes in an assemblage of diurnal leaf-litter frogs in central Amazonia. All species in this assemblage change the type and size of prey as they grow. An ordination of diet composition was significantly associated with frog size and species-specific behaviour. However, a partial Mantel analysis indicated that species explained about 1.5 times more of the variation in diet overlap between individuals than frog size. Diet and foraging activity are correlated in juveniles, but not in adults, and this result holds whether species are considered as statistically independent observations or whether relationships are analysed using phylogenetically independent contrasts. This study showed that the partitioning of food resources between species changes with the population size structures. Thus, intraspecific and interspecific changes in diet, coupled with different patterns of juvenile recruitment, cause diet segregation among species due to temporal segregation of equivalent size classes. Received: 25 August 1997 / Accepted: 1 April 1998     

Feeding guild structure of a rocky intertidal fish assemblage in central Chile

The identification and analysis of the guild structure of vertebrate assemblages has played a fundamental role in the understanding of the underlying mechanisms responsible for their community organization and structuring. This approach generally has not been undertaken for temperate water intertidal fish assemblages. In central Chile, fishes are important components of the intertidal community, but no studies attempting to understand their organization and structuring have been done. In the present study, the diets of 13 of the most abundant species which inhabit tidepools in the rocky intertidal zone of central Chile were determined. A total of 660 fishes was collected at 5 sites: Los Molles, Con-Cón, Quintay, El Tabo, and Las Cruces. Dietary overlap between all species pairs was calculated and a phenogram of dietary similarity was constructed and analyzed using a bootstrapping technique to objectively determine guild membership. The results showed that the intertidal fish assemblage of central Chile can be divided into three feeding guilds: two guilds consisting of carnivorous species and one guild of omnivorous and herbivorous species. The possible causes and implications of the resulting guild structure and the potential effects of predation by these fishes on other components of the intertidal community are discussed.     

Specialization and noncompetitive resource partitioning among sponge-eating dorid nudibranchs

Summary Habitat and food resource partitioning ecologically isolate six species of Pacific Northwest dorid nudibranchs. Food resources along a gradient of sponge skeletal structure are partitioned between two exploitive guilds. The guilds are characterized by mutually exclusive predatory and digestive adaptations which allow efficient processing of sponges with poorly- or well-organized skeletons. Habitats along a depth gradient are partitioned within guilds. For a dorid species, feeding rates, extraction efficiencies and food quality are virtually identical for sponges with the appropriate extreme (either poorly- or well-organized) and intermediate skeletal organizations, but growth and reproductive rates supported by the former prey type are twice those supported by the latter prey type. Prey types with the appropriate extreme skeletal organization are thus optimal food and specialization to that food is expected. When two divergent specialist species co-occur, food resource partitioning is demonstrable but arises from self-stabilizing specializations to maximize net energy accumulation and not from competitive interactions. Habitat partitioning is viewed as arising from prey distributions and dorid physiological tolerances. This system represents an example of morphological and behavioral specializations giving rise to resource partitioning as opposed to competition giving rise to resource partitioning and subsequent morphological and behavioral specializations.     

The guild structure of a community of predatory vertebrates in central Chile

Summary The trophic ecology of eleven predator species (Falconiforms: Buteo polyosoma, Elanus leucurus, Falco sparverius, Geranoaetus melanoleucus, Parabuteo unicinctus; Strigiforms: Athene cunicularia, Bubo virginianus, Tyto alba; Carnivores: Dusicyon culpaeus; Snakes: Philodryas chamissonis, Tachymenis peruviana) in two nearby localities of central Chile is analyzed. The localities exhibit the typical climate (hot-dry summers, coldrainy winters), and vegetation (chaparral), of mediterranean ecosystems. Densities of the staple prey (small mammals) were estimated by seasonal trapping during two years in both open and dense patches of chaparral.The trophic parameters examined are: 1) proportion of diurnal, crepuscular, or nocturnal prey found in the predators' diet; 2) relationship between abundance of different mammalian prey in the predators' diet, and in both open and densely vegetated habitat patches; 3) mean weight and variance of weight of small mammal prey consumed; 4) average weight of the predators; 5) food-niche breadth of the predators; 6) relationship between average weight of predators and mean weight of mammalian prey taken, its variance, and food-niche breadth; 7) overlap in food-niche between all the predator species; 8) guild packing of the predators. Parameters 1) and 2) are used to assess the importance of temporal and habitat segregation of the predators, respectively; parameters 3), 4), 5), and 6) provide information on the possibilities of partitioning the prey resources among the predators; parameters 1), 2), 7) and 8) are used to investigate the organization of the community in terms of guilds.Three niche dimensions seem to be important in determining the structure of the predator community: 1) hunting activity period (diurno-crepuscular, nocturno-crepuscular), 2) hunting habitat (open, or both open and dense patches), and 3) mean prey size taken. Segregation along these three axes results in generally low food niche overlaps (<54% in 47 of the 55 pairwise comparisons) among the predators, but it is not possible to determine whether this was produced by competitive interactions or stochastic differences. Three guilds (niche overlap >90% in pair-wise comparisons) can be recognized: a) the carnivorous-insectivorous guild formed by the diurnal raptors A. cunicularia and F. sparverius, which tend to hunt in open habitat patches; b) the herpetophagous guild formed by the diurnal snakes P. chamissonis and T. peruviana, which presumably hunt in open habitat patches; c) the carnivorous guild (highly specialized in the capture of two rodent species) formed by the diurnal raptors B. polyosoma, G. melanoleucus, P. unicinctus, and the carnivore D. culpaeus, which hunt in open habitat patches. The diurnal raptor E. leucurus is not clearly associated with any guild, and the only two nocturnal raptors in the community (B. virginianus and T. alba) exhibit marked differences in their trophic ecology.     

Diel activity of resident and immigrant waterbirds at Lake Turkana, Kenya

Of the 42 dominant species of waterbirds at Lake Turkana, Kenya, 14 foraged uniformly throughout the day and night, five foraged mostly during the night, five foraged during both the night and day but with diurnal peaks, 17 were exclusively diurnal and only one was exclusively nocturnal. Species with uniform feeding activity usually captured small prey, using tactile or visual plus tactile cues; most diurnal species captured large prey, using visual cues. However, some species which fed mostly at night, or uniformly, relied exclusively on visual cues. We found support from only one species that moonlight influenced foraging activities. Palaearctic immigrants spent significantly more time foraging than partial migrants and residents; they were also smaller and mainly microphagous. Only gulls and terns were restricted to diurnal feeding, presumably by their need to see and capture prey while flying. The other groups were formed by species which foraged uniformly over 24 h or partially by day or night. These patterns indicate that in most waterbirds feeding activities are not basically tied to any phase of the diel cycle. Since most waterbirds display some degree of nocturnal activity, time budget studies based only on diurnal observations are likely to be misleading.     

Diet and biology of the laughing owl Sceloglaux albifacies (Aves: Strigidae) on Takaka Hill, Nelson, New Zealand

The faunal composition of two Holocene fossil deposits of small vertebrates provided new information on the diet and biology of Sceloglaux albifacies , a strigid owl endemic to New Zealand. The taxonomic composition and several measures of diversity of the prey accumulation are given. Most taxa in the deposit had a mass of 50-150g, but species up to 400g were also present. The owl was a generalist feeder, but the prey biomass distribution showed that a few taxa provided most of its energy requirements. Changes in the diet appeared to coincide with the appearance of Rattus exulans , the Polynesian rat, and the consequent decline or extinction of several prey. The ecologies of extant taxa represented in the deposit suggest that the owl was primarily a nocturnal forest species. Many prey taxa were terrestrial. Species richness was higher for both diurnal (by 50%) and nocturnal (by 63%) vertebrates in the deposit than in the present fauna around the site. Analysis of possible guilds in the pre-human and present faunas of Takaka Hill suggests that ground-frequenting taxa were most severely affected by extinctions; three guilds vanished entirely.     

Variation in the guild composition of herbivorous insect assemblages among co‐occurring plant species

Variation in plant traits among plant species may promote the development of a characteristic functional assemblage of insect herbivores associated with each plant species. However, only a small number of studies have detailed the representation of several herbivore guilds among co‐occurring plant species to determine whether the functional structure of herbivorous insect assemblages varies widely and consistently among plant species. The present study provides one of the few published data sets reporting on the density of several guilds of insect herbivores among numerous plant species. Variation in guild associations with plant phenology and season are also described. Insect herbivores were divided into 10 guilds, and the representation of these guilds was examined for 18 co‐occurring plant species. Guild densities and assemblage composition varied significantly among plant species, even when variation over time was taken into account. Variation in guild densities and assemblage composition were not strongly related to the taxonomic relationships of the plants. The highest densities of several guilds occurred in spring and summer, although other guilds were not strongly seasonal. Certain guilds were strongly associated with the presence of new leaves, whereas other guilds appeared to prefer mature leaves. This resulted in assemblage differences between samples containing new and mature leaves and samples containing mature leaves only. Even though the timing and duration of leaf and flower production varied among plant species, this did not explain all variation in guild densities among plant species. It is suggested that additional factors, including plant traits, are contributing to the wide and consistent variation in herbivore assemblage composition among plant species.     

Diets and trophic guilds of small fishes from coastal marine habitats in western Taiwan

The diets and trophic guilds of small fishes were examined along marine sandy beaches and in estuaries at depths <1·5 m in western Taiwan, Republic of China. Copepods were the most frequently identified item in fish guts, indicating they are key prey for the fish assemblages studied. Piscivore, crustacivore, detritivore, omnivore, zooplanktivore and terrestrial invertivore trophic guilds were identified. The zooplanktivore guild contained the most fish species. Maximum prey size consumption was positively correlated with standard length (L_S) in seven species and at the assemblage level and negatively correlated with L_S in a single detritivorous species. The diet data and trophic guild scheme produced by this study contribute to an understanding of coastal marine food webs and can inform ecosystem‐based fisheries management.     

Local‐ and landscape‐level effects of land use change on bird diversity in Abiata‐Shalla Lakes National Park,Ethiopia

Understanding the effects of anthropogenic disturbances on biodiversity is important for conservation prioritization. This study examined the effects of vegetation degradation on bird diversity in Abiata‐Shalla Lakes National Park, Ethiopia. We surveyed birds and vegetation structure between January and March 2015 in disturbed (impacted by settlement and agriculture) and undisturbed (not impacted) transects of two vegetation types (savannah woodland and gallery forest). We compared between disturbed and undisturbed transects at local (within vegetation types) and landscape (across vegetation types) levels: (a) avian species richness of the entire assemblage and feeding guilds and (b) species assemblage composition. We found significantly greater mean and total bird species richness of the entire assemblage and insectivore and granivore feeding guilds in the undisturbed transects, while the nectarivore guild was totally absent in the disturbed transects. We also found significant differences in bird species assemblage composition between the disturbed and undisturbed transects both within and across the vegetation types, and bird species assemblage composition at the landscape level was positively correlated with tree abundance and understorey vegetation height. In conclusion, our results demonstrate and add to the increasing body of evidence concerning the adverse effects of human‐induced vegetation change on bird diversity.     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.     

Feeding ecology of thirteen syntopic species of anurans in a seasonal tropical environment

Summary Thirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.