Differential Use Of Food Resources Research Articles

Differential use of trophic resources between an exotic and a coexisting native snail

Knowing the interactions between exotic and native species is essential to establish possible threats to the local fauna. In this study, we assessed the use of food resources and diet overlap between a recently introduced snail, Sinotaia quadrata, and a native species, Pomacea canaliculata. We analyzed the gut content and stable isotope of snails and resources in a lowland stream where both species coexist. Both Schoener’s and isotope dietary overlap indexes supported dietary overlap. Conversely, gut content analysis showed differences in consumption: S. quadrata consumed more detritus and diatoms than P. canaliculata, whose diet was characterized by detritus and macrophyte remains. Macrophytes were the resource that most contributed to the diet of both species, as shown by stable isotope mixing models. The combination of both techniques, gut content and stable isotope analysis, indicated that S. quadrata consumed macrophyte detritus while P. canaliculata ate fresh macrophytes. This difference indicates differential use of food resources between the studied species coexisting in a lowland stream. Although no negative trophic interaction was found, we highlight the importance of continuing to monitor interactions for other resources and studying possible risks to the local fauna.

Macrophytes in tropical shallow lakes: An important food item to benthic entomofauna or an underused resource?

AbstractAlthough macrophytes are known to increase benthic diversity in lakes, the importance of this resource as food for the insects living at the bottom of these ecosystems are still poorly understood. This study assessed the diets of benthic Chironomidae and Campsurus (Ephemeroptera) in two environments: a lake with macrophytes (M+) and another without macrophytes (M−). We expected a differential use of food resources in M+, where plant tissue is particularly important for the aquatic insects’ diet. The diet of 734 individuals from 16 taxa were analyzed. Contrary to expectations, benthic insects consumed low amounts of plant tissue. This finding led us to investigate whether the presence of macrophytes in lakes would indirectly contribute to the benthic insects’ feeding, as more food resources were explored in M+ and a spatial variation of resources intake was observed in this lake, in contrast to the homogeneous feeding in M−. We highlight that macrophytes were responsible for the organic matter build‐up in the sediment, especially at the lake region dominated by these plants, and contributed to increase the deposition of high‐quality amorphous organic matter, which favored taxa in M+ that fed exclusively on this item. The lower diversity of food items exploited in M−, and the Tanypus alga‐based diet in this lake, indicates the low quality of organic resources in its sediment. Although macrophytes were indirectly beneficial for benthic insects’ feeding, we found that this is not an attractive resource for prompt ingestion by most benthic taxa.

Coexisting small fish species in lotic neotropical environments: evidence of trophic niche differentiation

Differences among species and their ecological requirements are considered fundamental in determining the outcome of species interactions as well as in coexistence. Thus, species that co-occurs tends to differ in the use of resources as a way to mitigate the effects of interspecific competition, facilitating interactions between pairs of species. So, this study used a set of seven small-sized characid species with similar morphology and feeding strategies, in order to investigate the hypothesis that the coexistence these species is facilitated by the differential use of food resources. Samplings were conducted in the rivers Verde and Sao Domingos, Upper Parana River basin, Brazil, in hydrological periods rainy and dry. The analysis of 1055 stomach contents, by the volumetric method, indicated that the species consumed mainly allochthonous items, such as seeds, terrestrial plants and insects. In addition, they showed inter- and intraspecific differences in the diet composition between hydrological periods, which allowed the identification of items that particularise each species and contribute to the trophic segregation between them. Despite the wide variety of food items used, it was not possible to observe a consistent pattern of widening or narrowing of the food spectrum between hydrological periods, as expected. The trophic niche overlap showed intermediate and low values in both periods. In this sense, resource partitioning among species of small characids, facilitated by exploitation of different preferential resources as well as the intraspecific variation in response to seasonal availability of resources, became evident. The alternation of items and proportions of items in the diet as well as changes in feeding behaviour in opportune moments was probably the key for the coexistence of these species.

Dietary partitioning between sympatric species of spiny lobster in a coral reef system

Throughout the Wider Caribbean Region, the spotted spiny lobster, Panulirus guttatus (Latreille, 1804), dwells and forages exclusively in coral reef habitat after post-larval settlement, whereas its sympatric species, the Caribbean spiny lobster, Panulirus argus (Latreille, 1804), undergoes ontogenetic habitat shifts, with smaller individuals dwelling in reef lagoon habitats and larger individuals dwelling in reef habitats, but exhibiting broad foraging ranges. Stomach content, and carbon and nitrogen stable isotopes analyses were used to examine dietary partitioning between co-occurring P. guttatus and reef-dwelling P. argus in a coral reef system off Mexico. Both species fed on a wide variety of invertebrates, but mollusks contributed more to the diet of P. guttatus and crustaceans to the diet of P. argus. The two species had different ranges of isotopic composition and each filled a unique trophic position within the local food web. A Bayesian mixing model revealed a distinct contribution of different food sources to the diet of these lobsters. Reef herbivores were the primary food source for P. argus and an important food source for P. guttatus, but the latter also consumed more carnivores, resulting in a higher trophic position relative to P. argus. The isotopic niche space, delineated by means of bivariate ellipses, exhibited no overlap between species, and P. argus exhibited a significantly larger niche area than P. guttatus. These results suggest that, in addition to a differential use of habitat resources, a differential use of food resources facilitates the local coexistence of these two congeners.

Inter and intraspecific differences in food resources selection and use in captive Philander frenatus and Didelphis aurita (Didelphimorphia; Didelphidae)

The opossums Philander frenatus and Didelphis aurita are sympatric throughout most of their distribution ranges and share several ecological traits, including natural diet. However, experimental studies on feeding habits of didelphid marsupials in captivity have revealed important differences between the nutritional contents of their diets, based on experimental food choice. Our aim was to assess inter and intraspecific differences in the diets of the two species. We hypothesized that comparisons of inter and intraspecific food habits variations in captivity can provide insights to understand the effects of differential use of food resources on niche differentiation and diversification. Thus, weused a cafeteria test with 26 different kind of foods. Food selection and use by the two specieswere analyzed and calculated niche breadth (Czekanowski’s Proportional Similarity - PS index) and overlap (Pianka’s index). Both P. frenatus and D. aurita had similar diets between sexes and age classes. However, D. aurita specimens used or tried a broader range of resources than those of P. frenatus for all compared categories. In P. frenatus males had a more generalist diet than females. Adults of this species were more generalist than younger specimens, and juveniles and subadults had similar indexes. In D. aurita the preferred diet was also very similar across sexes and age classes. In this species, males have a narrower diet than females. In juveniles niche breadth and diet amplitude were superior to those of subadults, while adults had the highest indexes of all three age classes. There was a high dietary overlap in all intraspecific, and interspecific comparisons performed. Our results show that selection and use of food resources in field and in laboratory coincided and are complementary, but intraspecific analysis revealed different strategies of food use in each species, which in nature may influence in niche partitioning and affect trophic structure in mammal communities.

Feeding Habits of Introduced Black Rats, Rattus rattus, in Nesting Colonies of Galapagos Petrel on San Cristóbal Island, Galapagos.

Introduced rodents are responsible for ecosystem changes in islands around the world. In the Galapagos archipelago, their effects on the native flora and fauna are adverse, including the extinction of endemic rodents in some islands and the reduction in the reproductive success of the Galapagos petrel (Pterodroma phaeopygia) in its nesting zones. Understanding the feeding behavior of introduced rodents and their trophic interactions with native and non-native species on islands, can assist in the design of management strategies and conservation plans of invasive and endemic species respectively. Four petrel nesting colonies were monitored during June 2013 on San Cristóbal Island (El Plátano, El Junco, San Joaquín, and La Comuna). The feeding habits of black rats were evaluated by analyzing stomach contents and stable isotopes in hair. Three species of introduced rodents were captured. R. rattus was the most abundant at all sites (n=43, capture success (CS) = 55.8%), followed by the house mouse, Mus musculus (n = 17, CS = 37.8%), and the Norwegian rat, R. norvegicus (n = 4, CS = 4.5%), captured only at La Comuna. The omnivorous black rat ate mostly plants (98%) and arthropods (2%). Intact seeds of Miconia robinsoniana were the main food at all sites (relative abundance=72.1%, present in 95% of the analyzed stomachs), showing the black rats’ possible role in the archipelago as endemic seed dispersers. There was no evidence of petrel’s intake; however, its possible consumption is not discarded at all. The δ15N and δ13C analysis corroborated the primarily herbivorous diet of black rats. The isotopic signatures of the three rodent species reflect the inter- and intra-specific differential use of food resources. Black rat showed a wider diet in La Comuna, which was related to a lower availability of its primary prey and its ability to adapt to the available resources in its habitat.

Food resource partitioning in syntopic nectarivorous bats on Puerto Rico

Abstract:Understanding the dietary needs of syntopic species is essential for examining species coexistence and resource partitioning. We analysed stable isotopes of carbon (δ13C) and nitrogen (δ15N) to estimate the diet of two putative nectarivorous bats on Puerto Rico, the brown flower bat (Erophylla bombifrons) and the Greater Antillean long-tongued bat (Monophyllus redmani). Isotopic ratios of δ13C and δ15N were obtained from whole blood of both species of bat and tissues of available plant foods and insect prey over 15 wk at the same locality. We used a concentration-dependent Bayesian mixing model to determine probability distributions of feasible dietary contributions for major potential foods used by each species of bat. Additionally, separate dietary estimates were conducted for males and non-reproductive, pregnant and lactating females to determine differences due to reproductive condition. Insects were an important source of protein for M. redmani, whereas E. bombifrons obtained most of its protein from plants. In both species of bat, lactating females had lower assimilated nitrogen than males, suggesting more reliance on plants for protein. We observed no intraspecific differences in assimilated carbon among reproductive conditions. Flight and lactation are energetically expensive and may explain the increased consumption of high-energy foods, such as fruit or nectar, in lactating female bats. Comparison of isotopes between E. bombifrons and M. redmani illustrate the differential use of food resources by these insular syntopic species of bat.

Low Functional Redundancy in Sponges as a Result of Differential Picoplankton Use

Understanding the way that closely related co-existing species utilize resources is important for explaining biodiversity patterns and understanding how organisms contribute to ecosystem functioning. Here we investigated the utilization of food resources by sponges to determine if different sponge species from the same habitat utilize different fractions of their picoplanktonic food resources, and examined the validity of treating sponges as a single trophic group in functional diversity assessments. Using flow cytometry, we demonstrated that different groups of sponge species have different retention efficiencies for different types of picoplankton, providing evidence for differential use of food resources among different sponge species living in the same habitat. Although the mechanisms to explain these differences remain undetermined, we propose that this differential food use means that the feeding activities of sponges should not be considered as a single functional role.

Differential use of food resources by dominant fish of San Ignacio Lagoon, Baja California Sur, Mexico.

The use of food resources in five of the most abundant fish species (Occidentarius platypogon,Cynoscion parvipinnis, Menticirrhus undulatus, Trachinotus paitensis and Heterodontus francisci) in San Ignacio Lagoon, Baja California Sur, Mexico is described. Prey composition, seasonal changes, diet breadth, trophic diversity and trophic overlap were analyzed. Forty nine prey items were identified, grouped into six taxonomic groups: crustacea, molluska, osteichthyies, anellida, equinodermata and sipunculida. Crustaceans and mollusks were the most important items recorded, representing over 75% of the identified prey. The crustaceans Callinectes bellicosus, Penaeus californiensis, Squilla spp., megalop larvae ofportunids and the mollusks Donax spp., Lucapinella milleri, Anachis spp., and Bittium spp. were the most important prey in the fish species analyzed. Differences in the prey composition and seasonal changes were observed, as well as seasonal changes in the diet breadth. All the predators examined had low percentages of breadth of diet, being characterized as opportunists with low levels of trophic diversity. There was only one case of higher prey overlap between O. platypogon and C. parvipinnis. We concluded that food resource partitioning is very important only in those fish species with higher overlap in their diets. Differences in bucal morphology seem related to prey selection.

Gut length plasticity in perch: into the bowels of resource polymorphisms

Resource polymorphisms, intraspecific variation in morphology due to differential resource use, are common across a wide range of animal taxa. The focus in studies of such polymorphisms has been on external morphology, but the differential use of food resources could also influence other phenotypic traits such as the digestive performance. In the present study, we experimentally demonstrate that Eurasian perch (Perca fluviatilis L.) display adaptive plasticity in gut length when exposed to different food types. Perch fed a less digestible food type developed relatively longer guts compared to fish fed a more easily digested food type. This divergence in gut length was also apparent under natural conditions because perch inhabiting the littoral and pelagic habitats of a lake differed in resource use and relative gut length. Despite that the digestive system in perch is plastic, we found that individuals switching to a novel food type might experience an initial fitness cost of the diet switch in the form of a temporary reduction in body condition. These results show the importance of gut length plasticity for an ontogenetic omnivore but also a cost that might prevent diet switching in polymorphic populations.

Latitudinal gradients in Atlantic reef fish communities: trophic structure and spatial use patterns

Trophic strategies and spatial use habits were investigated in reef fish communities. The results supported the hypothesis of differential use of food resources among tropical and higher latitude reef fishes,i.e. the number of species and relative abundance of fishes relying on relatively low‐quality food significantly decreased from tropical to temperate latitudes. The species : genus ratio of low‐quality food consumers increased toward the tropics, and was higher than the overall ratio considering all fishes in the assemblages. This supports the view that higher speciation rates occurred among this guild of fishes in warm waters. It was also demonstrated that density of herbivorous fishes (the dominant group relying on low‐quality food resources) in the western Atlantic decreased from tropical to temperate latitudes. Spatial use and mobility varied with latitude and consequently reef type and complexity. Fishes with small‐size home ranges predominated on tropical coral reefs.

DIETARY OVERLAP BETWEEN WOLVES AND COYOTES IN NORTHWESTERN MONTANA

We studied effects of recolonizing wolves (Canis lupus) in the North Fork of the Flathead area of northwestern Montana on the diets of coyotes (C. latrans) from 1994 to 1997. Wolf and coyote diets differed in frequency of occurrence of prey species during 3 of the 4 summers and winters (P < 0.001) during the study. Coyote diets contained more murid prey items, and wolf diets contained more deer (Odocoileus virginianus and O. hemionus) in the summer and elk (Cervus elaphus) in the winter. Coyotes and wolves ate prey of different size during both the summer (P < 0.001) and winter (P < 0.001) months in 1994–1996: wolves took a greater proportion (P < 0.001) of large (>45 kg) prey species and coyotes, small (<2 kg) prey (P < 0.001). Wolves selected a larger proportion of adults (P < 0.001), whereas coyotes selected a larger proportion of juveniles (P < 0.001) during summer. We believe that differential use of food resources facilitates coexistence of wolves and coyotes in the North Fork of the Flathead area.

Population studies and reproduction of the feral cattle (Bos taurus) of Amsterdam Island, Indian Ocean

Amsterdam Island has supported a population of feral cattle since 1871. In 1987 a fence was erected across the island, and in 1988 and 1989 the whole population (n = 1059) living south of the fence (study area) was removed. Nine hundred and sixty one culls were analysed. Age of calves indicated that reproduction was seasonal, as 78% of births occurred within four months. Age at first calving ranged from 2–4 years. An estimation of the fertility (rate of conception) was 0‐73 foetuses per cow per year.In the north part of the study area, 50–80 males have been killed for beef each year since 1951. The effect of hunting was analysed and a zone where cattle had been free from human interference was defined. In this zone sex ratio was biased towards males (252 M:201 F), owing to female biased mortality in individuals older than three years. The cause of the biased mortality might be a differential use of food resources between sexes.

Differential use of food resources by the instars of Chaoborus punctipennis

SUMMARY. 1. Differential use of food resources by instars I‐1V of Chaoborus punctipennis was examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I‐II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard‐bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans in C. punctipennis diets were quantified using crop content analyses.2. All four instars ingested large, flagellated phytoplankton (mainly Dinobryon and Ceratium). This unexpected result suggests that the effects of phytoplankton on Chaoborus growth and survival should be investigated. All instars also consumed rotifers (mainly Kellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainly Daphnia, Bosmina and Diaphanosoma). Small rotifers (Gastropus spp., Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodonta and Keratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g. Ascomorpha, Collotheca and Holopedium) were rarely ingested.3. Developmental increase in gape diameter of C. punctipennis seemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard‐bodied prey in C. punctipennis crops were always less than gape diameter. The relationship between prey body width and Chaoborus gape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard‐bodied prey taxa in diets of other Chaoborus species.4. All four instars of C. punctipennis selected soft‐bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotifer T. similis and the protozoan Difflugia sp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer, Asplanchna. Prey value (prey weight ingested per unit handling