Important Prey Group Research Articles

Pitcher Dimorphism, Prey Composition and the Mechanisms of Prey Attraction in the Pitcher Plant Nepenthes Rafflesiana in Borneo

1 The pitcher plant Nepenthes rafflesiana Jack produces dimorphic pitcher types. Upper pitchers catch more flying prey than lower pitchers. The most important single prey group in both pitcher forms was Formicidae. 2 Both pitcher forms possess ultraviolet (UV) patterns which were associated with the site of the major nectaries, causing it to stand out in contrast to the adjacent area. Manipulation of these patterns in upper pitchers confirmed their role in the attraction of prey. 3 Upper pitchers produce a fragrance which is attractive to flying prey. The combination of visual and olfactory cues accounted for the greater prey attraction of upper over lower pitchers. This is confirmed by the pitchers of N. rafflesiana var. elongata, which possess neither UV patterns nor fragrance, and catch significantly less prey than the typical form. 4 Lower pitchers resting at ground level, where densities of potential invertebrate prey are highest, are less than optimally attractive. This may reduce the amount of prey caught, thus preventing overloading and consequent putrefaction of the contents, and death of the pitchers.

HABITOS ALIMENTARIOS DEL COYOTE (CANIS LATRANS) EN LA SIERRA DEL AJUSCO, MEXICO

Se presentan los resullcidüs del análisis de los residuos encontrados en 238 excretas de coyote colectadas en la Sierra del Ajusco, en los estados de México, Morelos y el Distrito Federal, durante un período de dos años (1992 y 1993). Los resultados obtenidos indican que en esta región el coyote se alimenta principalmento de mamíferos (79.0%) y en menor grado por aves (7.8%). Entre los mamíferos, los mayores porcentajes de aparición (N = 409) se encontraron en los lagomorfos (30.1 %), roedores (24.0%) y mamíferos domésticos (22.0%). Las especies con el mayor porcentaje de aparición fueron Microtus mexícanus (12.0%), Romerolagus diazi (10.8%). Ovis aries (10.8%) y Sylvilagus floridanus (10.5%). En otras áireas de bosques templados de Estados Unidos, el coyote es importante depredador de venados (20.5%, 10.2%.), no asi en la Sierra del Ajusco (0.5%). Comparativamente con otras regiones de América, en la Sierra del Ajusco se presenta el mayor porcentaje de aparición de mamíferos domésticos (21.7%) lo que puede indicar el grado de perturbación antropológica de la región y ei carácter oportunista de los hábitos alimentarios del coyote.

Feeding Ecology of Deepwater Lutjanid Snappers at Penguin Bank, Hawaii

Deepwater snappers are a valuable component of fisheries on slopes and banks in Hawaii and in much of the worldˈs tropics. Their ecology and trophic relationships in these deepwater habitats are poorly known. Line fishing in this study simultaneously collected six of the seven lutjanid species that commonly occur in the major deepwater snapper fishery at Penguin Bank, Hawaii. The catch rate of each species showed diel variability; the patterns of some species were distinctly different. The depth distribution of feeding, as indicated by depth of capture, differed considerably among species; all species were taken within several meters of the bottom. Size (fork length) of the predator species did not appear to be stratified by time of capture (daylight versus darkness) or median capture depth. Regurgitation of gut contents seemed to be reduced when fish were retrieved at a rate that was slower than used in commercial practice but rapid enough to prevent death or morbidity while hooked. The food remaining in line-caught specimens appeared to be representative of what was originally eaten. The six snapper species ate considerable amounts of a wide range of pelagic animals and demersal fishes and much smaller quantities of a few invertebrate benthic groups. Etelis coruscans, Etelis carbunculus, and Aprion virescens formed a distinct, primarily piscivorous feeding guild. Pristipomoides filamentosus and Pristipomoides sieboldii formed a distinct guild dominated by zooplankton feeding. The few specimens of Pristipomoides zonatus appeared somewhat intermediate in diet. Important planktonic prey groups included crustaceans, pteropods, and large, pelagic, colonial urochordates (e.g., salps). Urochordates made a significant contribution to the diet even for some of the primarily piscivorous species. Major diel and seasonal shifts in diet were found only in P. filamentosus; they involved the relative proportions of fish, and especially of the major planktonic groups. Our information on diet composition and depth and time of feeding (catch) suggests that considerable resource partitioning occurs among these deepwater snappers.

Feeding Habits of Northeast Atlantic Harp Seals (Phoca groenlandica) along the Summer Ice Edge of the Barents Sea

Stomachs from 58 harp seals (Phoca groenlandica) from the northern part of the Barents Sea were collected between August 20 and September 5, 1987. Fifty-six of the stomachs contained identifiable remains. The amphipod Parathemisto libellula was the most common food item, found in 98% of the seal stomachs and constituting 57.9% of the total volume. Fish were the second most important prey group, with Arctic cod (Boreogadus saida) as the dominant species followed by Nybelin's sculpin (Triglops nybelini) and Greenland halibut (Reinhardtius hippoglossoides). Decapods, mainly Pandalus borealis, were also common as prey of harp seals. No sex- or age-related differences in choice of food were found. From knowledge of the depths at locations where seals were collected and the presence of fresh benthic fishes in the seal stomachs, it is assumed that harp seals could forage at depths below 300 m.

Diet composition and prey selection in the lizard Lacerta monticola

We studied diet composition and prey selection in the lizard Lacerta monticola throughout its activity season. The most important prey groups in terms of numbers were Coleoptera, Diptera, Formicidae, and Araneae. Comparison of diet composition in the adult lizards with estimates of prey availability indicated that lizards exhibited precisely defined patterns of prey selection. Electivities were negative for prey < 3 mm in length and generally positive for larger prey, despite the higher relative abundance of the former group in the environment. Electivity scores for individual prey taxa were positively correlated with their length, and lizards preferentially consumed larger individuals belonging to the taxa containing smaller animals. Relative availability of the four major prey taxa fluctuated considerably throughout the year. In spite of these changes, monthly rates of consumption of Araneae and Diptera remained almost constant. Variations in monthly electivity scores were negatively correlated with relative availability of three (Coleoptera, Diptera, and Araneae) of the four major prey taxa. These results fit the predictions of prey-selection models based on nutrient constraints.

Numerical and Functional Responses of Kestrels, Short‐Eared Owls, and Long‐Eared Owls to Vole Densities

We studied numerical and functional responses of breeding European Kestrels (EK) (Falco tinnunculus), Short—eared Owls (SO) (Asio flammeus), and Long—eared Owls (LO) (Asio otus) during 1977—1987 in 47 km2 of farmland in western Finland. The pooled mean yearly breeding density varied from 0.1 to 2.4 pairs/km2. The number of nesting EKs (range 2—46 pairs), SOs (0—49), and LOs (0—19) fluctuated in close accordance with the spring density of Microtus (M. agrestis and M. epiroticus) voles. The mean yearly number of fledglings produced per pair ranged from 0.4 to 3.8 and, for each species, was positively correlated with spring density of Microtus voles. Due to their high degree of mobility, EKs, SOs, and LOs were able to track the population fluctuations of their microtine prey without time lags. An increase in microtine densities caused a rapid immigration into the study area and a decrease caused a rapid emigration from the area. Microtus voles were the most important prey group by mass in the diet of each species. Water voles, bank voles, shrews, and small birds were the most frequent alternate prey. The spring density of Microtus spp. was positively correlated with the percentage of these voles in the diet of EK, SO, and LO. The pooled functional response curve of these three raptor species to the fluctuating densities of Microtus spp. was close to linear, indicating that consumption rates are independent of vole densities. Breeding EKs, SOs, and LOs seemed to take a larger proportion of voles available in peak years than in low ones.

Ecología trófica de Lacerta lepida en la provincia de León, noroeste de España

Abstract The diet of Lacerta lepida in the province of León (NW Spain) was studied through the analysis of 286 faecal pellets collected during May-August. Insecta were the numerically most important prey group, and always represented more than 85 % of prey numbers. Coleoptera and Hymenoptera were the dominant orders. Other important prey groups were Heteroptera and Arachnida. The number of Orthoptera consumed increased gradually from May to August. With respect to the occurrence frequency of prey in the faecal pellets, Coleoptera and Hymenoptera occurred in more than 75% at all times. The lowest trophic diversity was detected in june-july. Seasonal changes in the diet were noteworthy within short-terms and augmented in the long-term. The average length of the invertebrate prey was within the interval 9-14 mm. In terms of energy content, Vertebrata (43.82%), Coleoptera (15.77%), Orthoptera (14.40%) and Hymenoptera (13.95%) were the principal groups. L. lepida is considered to be an opportunistic feeder, although some prey groups are apparently selected.

Seasonal variation in the interactions between piscivorous fish, planktivorous fish and zooplankton in a shallow eutrophic lake

The interactions between the higher trophic levels in a shallow eutrophic lake were studied during the course of a year. Three fish species determined the main pathways of organic matter flow within the system: the predominantly planktivorous bream (Abramis brama), the obligate planktivorous smelt (Osmerus eperlanus), and the piscivorous pikeperch (Stizostedion lucioperca). Of the thirteen common zooplankton taxa Daphnia hyalina and cyclopoid copepods were utilized most by the planktivorous fish, while the large production of small cladocerans is almost left unutilized. The seasonal variations of production and consumption are large. This is mainly affected by seasonal variation of the water temperature. The production of O + smelt is efficiently utilized by the pikeperch. Being the most important zooplankton consumer, as well as the most important prey group, O + fish plays a key role in the Tjeukemeer food web.

Contribution to the Biology of the Spotted Wolffish (Anarhichas minor) in the Northwest Atlantic

Data on the biology of the spotted wolffish in the Northwest Atlantic were obtained in 1946-67 during research fishing with otter trawls and longlines. Length frequencies of males and females showed no consistent differences. The longest male was 118 cm and the longest female was 121 cm. Egg diameters and ovarian weights of mature fish indicated that spawning of most spotted wolffish occurred during or soon after July-August. Sexual maturity of females over most of the area began at sizes of 75-80 cm or larger, but there were indications that maturity may have begun at smaller sizes off West Greenland and on Flemish Cap. Males weighed more than females at the larger sizes. Weights of the larger size-groups in July-September were lower than in other quarters of the year, in agreement with the probable spawning period. The mean vertebral number of 684 spotted wolff ish was 77.64, with the range being 74-80. There were no significant differences in vertebral means throughout the area, although West Greenland and Flemish Cap data showed possibilities of being lower. The dorsal fin-ray mean for 45 specimens was 75.90, with the range being 74-77. The correlation between dorsal fin-ray and vertebral numbers was highly significant. Invertebrates and fish composed 77 and 23% by volume respectively of the stomach contents. Echinoderms, which constituted 52% of the volume, were the most important prey group.

The prey of web-building spiders compared with feeding experiments (Araneae: Araneidae, Linyphiidae, pholcidae, Agelenidae).

Feeding experiments with 2,520 prey animals show differences in consumption rate and palatability for four spider species (Zygiella x-notata, Linyphia triangularis, Tegenaria atrica, Pholcus phalangioides). A possible protection against predators by chemical defence is discussed with special regard to 30 species of Heteroptera. Chemical weapons possess an astonishingly low deterrent effect whereas thick chitinisation (Coleoptera) is found to give very effective protection. Studies of the actual prey of these webbuilding spiders gave similar results in Araneidae and Linyphiidae. Nematocera and Homoptera are the most important prey group. Hymenoptera, Coleoptera and Brachycera were seldom caught. In contrast to this, the prey of Tegenaria and Pholcus consists mainly of Brachycera, Coleoptera and Hymenoptera, whereas Nematocera and Homoptera are rarely caught. The prey animals are mostly of small size. Only Pholcus and Tegenaria catch larger specimens. An ecological classification of the prey of Linyphiidae and Araneidae shows high percentages of phytophagous and detritophagous insects. Compared to the potential prey (trap data), predators, parasites and pollinating insects are underrepresented in the actual prey.

The diet of Sand Martins during the breeding season

This study of insect remains in faeces found no particular selection for insects associated with water. Diptera and aphids were the more important prey groups for Sand Martins. There was evidence for differences in feeding ecology between British hirundines, based on prey size.

Food resource partitioning by the pufferfishes Sphoeroides spengleri and S. testudineus from Biscayne Bay, Florida

Partitioning of the food resources by two coexisting pufferfishes (Sphoeroides spengleri and S. testudineus) from Biscayne Bay, Florida, USA, was investigated. Gut contents from 453 bandtail and 339 checkered puffers were analyzed. The diets of both species consisted of a variety of benthic prey, but only crustaceans and molluscs were important prey groups. While differences were found in the proportions of general prey categories eaten by these fishes, both species consumed substantial quantities of brachyuran crabs, bivalves, and gastropods. Specific identification of the prey items within these three food categories revealed additional differences in prey between the two puffer species. This partitioning of the food resources by bandtail and checkered puffers was found between both species overall, between overlapping size ranges, and between both species' most abundant size group. Differences in food habits between these two fishes illustrate that congeners with virtually identical mouth structure and complete spatial overlap can significantly partition the food resources.