Analysis Of Diet Composition Research Articles

Foraging ecology of oceanic-stage loggerhead turtles Caretta caretta

We examined stomach contents (n = 12) and fecal samples (n = 4) in the first quantita- tive analysis of diet composition of oceanic-stage loggerhead turtles Caretta caretta from the North Atlantic Ocean. We found that loggerheads from the Azores are opportunistic carnivores that feed upon a variety of oceanic and pelagic organisms; our results also show that they exploited novel food resources, such as non-indigenous species. The diversity of prey species was positively correlated with loggerhead body size and volume of stomach contents. Because loggerhead body size was also positively correlated with stomach content volume, we were unable to determine whether increased prey diversity was a result of turtle foraging behavior or simply due to a larger sample volume from larger turtles. Ecological associations among prey species increase the diversity, and possibly the nutritional quality, of prey items, and periodic meteorological events can also increase the diversity of prey items available to loggerhead turtles. Aspects of the life history of some of these prey organ- isms, such as continued egg brooding, increase the nutritional value of prey items consumed by juve- nile turtles.

Composición y superposición de dietas en cuatro especies de Diplectrum (Perciformes: Serranidae) en el Pacífico central mexicano

Analysis of diet composition and overlap in four species of the genus Diplectrum (Perciformes: Serranidae) in the Mexican Central Pacific. The information of trophic interactions among species is essential to understand ecosystem function. To assess this in four Diplectrum species, we analyzed the stomach contents of 397 individuals caught using shrimp trawling nets off the coasts of Jalisco and Colima, Mexico. Main food component of D. eumelum were fish of the Order Pleuronectiformes, followed by shrimps (Metapenaeopsis spp). D. euryplectrum feeds mainly on crustaceans, with stomatopods (Squilla mantoidea) as main food items followed by shrimps and brachyurans. Fish and polychaetes had a low representation in the diet of this species. D. labarum feeds mainly on crustaceans, mollusks and fish. The stomatopod Eurysquilla veleronis contributed to with a high diet percentage by weight, followed by shrimps (mostly Solenoceraflorae) and brachyurans, as well as the squid Lolliguncula diomedae. Fishes (Ophidion spp.) were also an important component of the diet of this species. The most common preys of D. rostrum were crustaceans, mollusks, polychaetes and fish. The squid Lolliguncula diomedae and fishes of genus Ophidion were also well represented in the diet. Diet breadth index yielded significant differences between species. The number of diet items varied from 16 in D. euryplectrum to 6 in D. eumelum. The average value of overlap (0.247) was not significantly different (p = 0.118) from the expected one for a null model (0.174). The observed variance of the overlap index (0.071) was significantly higher (V = 0.025, p = 0.0004) than the value expected for a null model.

Seasonal Resource Selection, Recruitment, Diet Selection and Time Budgets of Bighorn sheep (Ovis Canadensis) in the Teton Range, Northwest Wyoming.

Many ungulate populations have lost access to their traditional migration routes and seasonal ranges, resulting in rapid and severe population declines. Some ungulate populations have been able to adapt to living year-round on one seasonal range and persist despite loss of migration. However, our understanding of how ungulates adapt their habitat selection and foraging strategies in order to compensate for migration loss is poor. This study investigates how a formerly migratory, now sedentary and isolated, bighorn sheep (Ovis canadensis) population persists year-round on high-elevation summer range in the Teton Range in northwest Wyoming. We captured and GPS-collared 20 bighorn ewes throughout the Teton Range in February 2008 and an additional 8 ewes in March 2009. In 2008, ninety percent of captured ewes were pregnant, and 100% were pregnant in 2009. During summers 2008 and 2009, we located and observed GPS-collared ewes, determined lamb survival, collected fecal samples for diet composition analysis, conducted vegetation surveys, and observed time-budgets. We found that 50% of lambs survived until at least mid-summer in 2008 and 60% survived in 2009. We observed differences in movement patterns between GPS-collared ewes during the summer seasons, ranging from 5 km to a maximum of 15 km. At this time, eight GPS-collared ewes have died (4 in avalanches, 1 from predation, and 3 unknown). This study is ongoing and will be completed in 2011. Results will directly contribute to management of this non-migratory and isolated bighorn sheep population, and will shed light on how a formerly migratory ungulate population has been able to persist on high-elevation range year-round

Recruitment, Diet Composition, and Time-Budgets of Bighorn Sheep (Ovis Canadensis) in the Teton Range.

Many ungulate populations have lost access to their traditional migration routes and seasonal ranges, resulting in rapid and severe population declines. Some ungulate populations have been able to adapt to living year-round on one seasonal range and persist despite loss of migration. However, our understanding of how ungulates adapt their habitat selection and foraging strategies in order to compensate for migration loss is poor This study investigates how a formerly migratory, now sedentary and isolated bighorn sheep (Ovis canadensis) population persists year-round on high-elevation summer range in the Teton Range in northwest Wyoming. We captured and GPS-collared 20 bighorn ewes throughout the Teton Range in February 2008 and an additional 8 ewes in March 2009. In 2008, ninety percent of captured ewes were pregnant, and 100% were pregnant in 2009. During summer 2008, we located and observed GPS-collared ewes, determined lamb survival, collected fecal samples for diet composition analysis, and observed time-budgets. We found that 50% oflambs survived until at least mid­ summer. Diet composition analysis is pending and we are waiting to combine time-budget observations with additional data that will be collected during summers 2009 and 2010. We observed differences in movement patterns between GPS-collared ewes during summer 2008, ranging from 5 km to a maximum of 15 km. At this time, six GPS-collared ewes have died (four in avalanches, one from predation, and one unknown). This study is ongoing and will be completed in 2010. Results will directly contribute to management of this non-migratory and isolated bighorn sheep population, and will shed light on how a formerly migratory ungulate population has been able to persist on high­elevation range year-round.

Feeding ecology of black anglerfish Lophius budegassa: seasonal, bathymetric and ontogenetic shifts

The diet of black anglerfish Lophius budegassa is described for the Cantabrian Sea (North Atlantic coast of Spain) from seasonal samples obtained onboard commercial vessels from January 1993 to December 1994. The stomach contents of fish caught on the continental shelf were examined, and differences in the diet in relation to age-class, season and depth were studied. The age-classes were grouped according to a cluster analysis of diet composition. As a result, three groups were obtained: the first two corresponded to juveniles between 2 and 7 years old, and the third one corresponded to adults between 8 and 15 years old. Although Micromesistius poutassou was an important prey for all ages, the youngest black anglerfish fed mainly on small benthic fish. In contrast, large prey species such as Phycis blennoides and Merluccius merluccius were eaten almost exclusively by adults. The diet composition changed during the year. The changes in the diet of black anglerfish older than 3 years were more related to seasonal differences than to between-size differences. These seasonal shifts were mainly marked by the varying importance of Trachurus trachurus and M. merluccius in their diet. Feeding intensity also showed seasonal variations, with a significant decrease in autumn. An indirect effect of depth on the feeding ecology of black anglerfish was also found, since both age and diet composition changed with depth.

Early‐ to late‐summer population growth and prey consumption by age‐0 pollock (Theragra chalcogramma), in two years of contrasting pollock abundance near the Pribilof Islands, Bering Sea

AbstractAcoustic survey data were used to estimate the abundance and distribution of age‐0 walleye pollock and zooplankton near the Pribilof Islands, Bering Sea, nursery area at two time periods in two consecutive years: the beginning of August, and mid‐September, of 1996 and 1997. The 1996 pollock year class ultimately produced a large adult cohort in the eastern Bering Sea, while the 1997 year class produced a below‐average adult cohort. Acoustic densities of age‐0 pollock were significantly lower in August – and declined more strongly from August to September – in 1997 than in 1996, indicating that the trend to adult cohort strength was already set by August. Diet composition analyses revealed that age‐0 pollock ate a much higher proportion of euphausiids in 1997 than in 1996, despite lower acoustic abundance of euphausiids in 1997. We infer that in 1996, age‐0 pollock experienced greater feeding success by August, with high concentrations of copepods available for smaller fish to consume, and high concentrations of euphausiids available for larger individuals. In 1997, age‐0 pollock had lower body condition in August and may have been limited by the availability of small (<2 mm) copepods. Bioenergetic modeling of prey consumption did not indicate a likelihood that age‐0 pollock would begin to deplete euphausiids until late August in 1996, and not at all between August and mid‐September in 1997.

Habitat use patterns of sympatric deer species on Rocky Mountain Arsenal, Colorado

Mule deer (Odocoileus hemionus) and white-tailed deer (O. viginianus) have been studied extensively as individual species throughout their respective North American ranges. However, comparatively little is known about interactions between these closely related species where they occur sympatrically. We studied spatial and habitat use patterns of sympatric mule deer and white-tailed deer at 3 hierarchical scales on Rocky Mountain Arsenal (RMA), Colorado, USA using radiotelemetry. Similarities in annual spatial distribution analyses (coarse scale) and diet composition analyses (fine scale) suggested the 2 species may have been competing for space and forage on RMA. However, seasonal differences in habitat use patterns resulted in spatial segregation, thereby allowing the 2 species to coexist. Mule deer used habitats primarily based on forage availability and secondarily for cover. White-tailed deer used habitats primarily based on availability of security cover. Habitat management and restoration efforts should consider maintaining existing composition and juxtaposition of vegetation associations that allow species to maintain seasonal allopatric distributions and, subsequently, coexistence. Increased deer population levels may lead to increased interactions between species.

Seasonal home range shift of red deer in a forest-agriculture area in southern Hungary

A long-term radiotelemetry study on red deerCervus elaphus Linnaeus, 1758 was carried out in a lowland forest-agriculture area in Hungary between 1993–2000. Previous observations suggested seasonal changes in population distribution between forested and agricultural habitat. Red deer concentrated in the forest during winter, but they appeared in the agricultural field during the vegetational period. We investigated the ranging behaviour, testing two alternative hypotheses: home range expansion and home range shift. Weekly radiotelemetry localisations revealed that 9 of 28 hinds showed a clear home range shift from the forest to the agricultural area for a prolonged time during the vegetational period. The remaining portion of the animals used a home range within the forest throughout the entire year. Diet composition analysis using indicator plant species showed that neither daily passages between habitats, nor home range expansion exists. These ranging behaviours were stable hence, if an animal shifted one year it shifted again in consecutive years andvice versa. Our results could be useful for the successful management of red deer populations in such complex habitats and to decrease agricultural damage.

Diet plasticity in blackcap (Sylvia atricapilla): The ability to overcome nutritional constraints imposed by agricultural intensification

We studied the consequences of agricultural intensification on the diet, nutritive balance, and body condition of an avian frugivore (blackcap, Sylvia atricapilla) that overwinters in southern Spain, and analysed dietary plasticity as an ability to overcome the effects of agricultural intensification. We considered two habitats with very different levels of land-use: Mediterranean shrublands dominated by wild olive trees, and highly managed olive orchards. We partitioned the diet into four basic components: olive fruits, non-olive fruits, arthropods, and non-fruit plant matter. Availability of these resources, which influenced diet composition and body mass, differed among habitats and reflected the degree of human land-use. Hedges in olive orchards increased the local fruit diversity, making the diet and body mass in olive orchards more similar to that of less altered habitats. Based on diet composition analysis in relation to energy, protein, and mineral intake, we suggest that blackcaps wintering in olive orchards select non-fruit plant matter (a rare item in other habitats) so as to balance their energy, protein, and mineral intakes. This is necessary because of the scarcity of resources other than olives in orchards. Moreover, such deficiency probably results in higher exploitation costs, which in turn may affect the birds’ physical condition. Remarkably, blackcap shows a high dietary plasticity among habitats during the autumn-winter period in southern Spain, which seems to help this species reside for part of the year in a large man-made region.

Predicting diet composition from body length in the zooplankton predator Leptodora kindti

Leptodora kindti and many other species of zooplankton predator range widely throughout temperate‐zone lakes, yet these species are rarely included in size‐based studies of food webs. This oversight derives mainly from a lack of predictive functions that quantify their effects on prey communities. With laboratory experiments I measured the handling time and phosphorus ingestion of L. kindti fed three cladoceran species radiolabeled with 33P as a tracer of dry weight (DW). In general, laboratory results show that predator body length exerts strong influence on maximum prey length, on prey handling time (and indirectly predation rate), and on prey profitability (expressed as µg DW ingested time−1) in systematic ways that may be useful in predicting predatory effects of L. kindti on natural prey communities. The prey‐capturing structure of L. kindti, called the trap basket, constrains the maximum length of prey that is consumable, and handling times on prey increase exponentially as prey length approaches the maximum dimensions of the trap basket. The empirical relationship is given by the following equation: Handling time = 1/[0.067(Trap basket length/Prey length — 1)0.536]. I use handling time and body length data to evaluate the predictive nature of two previously published regression models that relate L. kindti trap basket length to body length. This note offers a length‐based approach to analysis of diet composition in L. kindti that will hopefully encourage increased consideration of this species in future studies of food webs.

A causal analysis of diet composition in free ranging cattle in reed-dominated vegetation.

Theoretical and observed diets of free-ranging yearling cattle in an area of reed-dominated vegetation were related to constraints inherent to ruminants (rumination time as reflected in the zone of acceptable crude fibre content of the ration; rumen fill) and in more general terms, to requirements for minerals (Na, Ca, Mg, P), for protein and for metabolisable energy in order to balance the growth rate achieved by experimental animals. Theoretical diets in spring were mainly limited by feeding time; theoretical diets in summer and autumn were mainly limited by rumen capacity. The high proteinto-energy ratio in the forage species caused protein intake to exceed the animals' demands. Mineral intake was in excess of requirements except for sodium. Yearling cattle in our study area maximized their energy intake, with feeding time, rumen capacity and crude fibre content of the forage as important constraints.

Energy Expenditure and Water Flux in Three Sympatric Desert Rodents

Energy Expenditure and Water Flux in Three Sympatric Desert Rodents

Energy Maximizers and Time Minimizers: Theory and Reality

Energy Maximizers and Time Minimizers: Theory and Reality