Diet of wolves <Emphasis Type="Italic">Canis lupus</Emphasis> returning to Hungary

At the end of the nineteenth century, the wolf Canis lupus was extinct in Hungary and in recent decades has returned to the northern highland area of the country. The diet of wolves living in groups in Aggteleki National Park was investigated using scat analysis (n = 81 scats) and prey remains (n = 31 carcasses). Throughout the year wolves (average, minimum two wolves per year) consumed mostly wild-living ungulates (mean percent of biomass consumed, B% 97.2%; relative frequency of occurrence, %O 74.0%). The wild boar Sus scrofa was the most common prey item found in wolf scat (%B 35.6%) and is also the most commonly occurring ungulate in the study areas. The second most commonly occurring prey item in wolf scat was red deer Cervus elaphus (B% 32.8%). Conversely, prey remain analyses revealed wild boar as the second most commonly utilised prey species (%O 16.1%) after red deer (%O 67.7%). The roe deer Capreolus capreolus that occurs at lower population densities was the third most commonly utilised prey species. The importance of low population density mouflon Ovis aries, livestock and other food types was low. The results are similar to those found in the northern part of the Carpathian Mountains.     

Patterns of stable carbon isotope turnover in gag, <Emphasis Type="Italic">Mycteroperca microlepis</Emphasis>, an economically important marine piscivore determined with a non-lethal surgical biopsy procedure

To determine the feasibility of using stable isotopes to track diet shifts in wild gag, Mycteroperca microlepis, populations over seasonal timescales, we conducted a repeated measures diet-shift experiment on four adult gag held in the laboratory. Fish were initially fed a diet of Atlantic mackerel, Scomber scombrus, (mean δ¹³C = −21.3‰ ± 0.2, n = 20) for a period of 56 days and then shifted to a diet of pinfish, Lagodon rhomboids, (mean δ¹³C = −16.6‰ ± 0.6, n = 20) for the 256 day experiment. We developed a non-lethal surgical procedure to obtain biopsies of the muscle, liver, and gonad tissue monthly from the same four fish. We then determined the δ¹³C value of each tissue by isotope ratio mass spectrometry. For the gonad tissue we used the relationship between C/N and lipid content to correct for the influence of lipids on δ¹³C value. We observed a significant shift in the δ¹³C values of all of the tissues sampled in the study. Carbon turnover rates varied among the three tissues, but the shift in diet from mackerel to pinfish was clearly traceable through analysis of δ¹³C values. The turnover rates for muscle tissue were 0.005‰ day⁻¹, and for gonad tissue was 0.009‰ day⁻¹. Although it is generally thought that tissue turnover rates in ectotherms are driven primarily by growth, we found that metabolic rate can be a major factor driving tissue turnover in adult gag.     

Marine nutrient contributions to freshwater apex predators

Recent investigations into the nutrient cycling of coastal ecosystems have suggested that migratory or anadromous fish could be important vectors of marine nutrients. Anadromous fish have assimilated marine nutrients that would contribute to the nutrient budgets of freshwater systems by excretion, gamete release, or the decay of post-reproductive carcasses. However, the extent to which freshwater predators utilize marine material is not well understood. In systems where anadromous fish temporarily constitute a major portion of the fish community, they may contribute substantially to the diet of piscivorous fish and other predators. Here we show the contribution of anadromous blueback herring, shad, and alewife (Alosa) to diets of large, non-indigenous piscivorous catfish (Ictalurus furcatus) using δ³⁴S and δ¹³C. The spawning anadromous Alosa, captured in tidal freshwater, had enriched δ³⁴S and δ¹³C values compared to resident, native freshwater species. As a result of consuming the anadromous Alosa, the I. furcatus isotope signature shifted towards the marine signal. The isotope analysis revealed that anadromous fish contribute substantially to the diet of most captured I. furcatus. The percentage of anadromous Alosa carbon and sulfur that was incorporated into I. furcatus (≥38 cm total length) ranged from 0 to 84% and 10 to 69%, and had means (±SD) of 42 (±24) and 43 (±16)%, respectively. Although the δ¹⁵N signal of marine-derived biomass is enriched by approximately 3‰ relative to terrestrial or freshwater biomass, it was not as useful as δ³⁴S and δ¹³C for nutrient source owing to trophic fractionation. This study demonstrates that anadromous fish may be a significant source of nutrients to tidal freshwater apex predators. Received: 19 March 1999 / Accepted: 26 October 1999     

Effect of macrophyte diet and initial size on the survival and somatic growth of sub-adult <Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>: a laboratory experimental approach

Recently recruited urchins from the same brood, but with different initial sizes, may respond differently to similar environmental factors. The aim of this study was to assess and compare the effects of starvation and diet on the survival, growth rates in size and weight, and gonad index among small and large sub-adult purple sea urchins, Strongylocentrotus purpuratus. Small urchins ranged from 7.3 to 7.8 mm and large urchins from 11.8 to 14.1 mm (test diameters). Two independent experiments were performed. In the first experiment, sea urchins were fed during 22 weeks on Egregia menziesii (ad libitum) and for only 1 day month⁻¹ (starved condition). Feeding regime significantly affected survival, somatic growth rate in size and weight, and gonad index, with higher means in the ad libitum treatments than in starving conditions. A recurrent cannibalism event by conspecifics occurred in small sea urchins under starving conditions. In the second experiment, sea urchins were fed during 13 weeks ad libitum with four diets: kelp (E. menziesii), coralline algae (Bossiella orbigniana), eelgrass (Phyllospadix scouleri) and a mixed diet of the three species. Survival was not affected by diet or urchin size, but diet significantly affected somatic growth rate in size and weight and gonad index. Kelp promoted the highest growth rate (2.23 ± 0.21 mm month⁻¹), the mixed diet produced an intermediate growth (1.26 ± 0.21 mm month⁻¹), while the lowest values corresponded to coralline algae and the eelgrass (0.30 ± 0.12 and 0.10 ± 0.03 mm month⁻¹, respectively, means ± SE). The mean growth rate of small urchins (averaging all diets) was higher than in large specimens (1.17 ± 0.37 and 0.77 ± 0.28 mm month⁻¹, respectively).     

Invading white-tailed deer change wolf–caribou dynamics in northeastern Alberta

Human-caused habitat change has been implicated in current woodland caribou (Rangifer tarandus caribou) population declines across North America. Increased early seral habitat associated with industrial footprint can result in an increase in ungulate densities and subsequently those of their predator, wolves (Canis lupus). Higher wolf densities can result in increased encounters between wolves and caribou and consequently higher caribou mortality. We contrasted changes in moose (Alces alces) and deer (Odocoileus spp.) densities and assessed their effects on wolf–caribou dynamics in northeastern Alberta, Canada, pre (1994–1997) versus post (2005–2009) major industrial expansion in the region. Observable white-tailed deer (O. virginianus) increased 17.5-fold but moose remained unchanged. Wolf numbers also increased from approximately 6–11.5/1,000 km². Coincident with these changes, spatial overlap between wolf pack territories and caribou range was high relative to the mid-1990s. The high number of wolf locations in caribou range suggests that forays were not merely exploratory, but rather represented hunting forays and denning locations. Scat analysis indicated that wolf consumption of moose declined substantively during this time period, whereas use of deer increased markedly and deer replaced moose as the primary prey of wolves. Caribou increased 10-fold in the diet of wolves and caribou population trends in the region changed from stable to declining. Wolf use of beaver (Castor canadensis) increased since the mid-1990s. We suggest that recent declines in woodland caribou populations in the southerly extent of their range have occurred because high deer densities resulted in a numeric response by wolves and consequently higher incidental predation on caribou. Our results indicate that management actions to conserve caribou must now include deer in primary prey and wolf reduction programs. © 2010 The Wildlife Society     

Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet,Southeast Alaska

Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska. In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks.     

Marine-derived nitrogen and carbon in freshwater-riparian food webs of the Copper River Delta,southcentral Alaska

After rearing to adulthood at sea, coho salmon (Oncorhynchus kisutch) return to freshwater to spawn once and then die on or near their spawning grounds. We tested the hypothesis that spawning coho salmon return marine N and C to beaver (Castor canadensis) ponds of the Copper River Delta (CRD), Cordova, southcentral Alaska, thereby enhancing productivity of the aquatic food webs that support juvenile coho salmon. We sampled three types of pond treatment: (1) natural enrichment by spawning salmon, (2) artificial enrichment via addition of salmon carcasses and eggs, and (3) ponds with no salmon enrichment. All ponds supported juvenile coho salmon. Seasonal samples of stable isotopes revealed that juvenile coho salmon, threespine sticklebacks (Gasterosteus aculeatus), caddisfly larvae, leeches, and chironomid midge larvae were enriched with marine N and C. The aquatic vascular plants bur reed (Sparganium hyperboreum), pondweed (Potamogeton gramineus), and mare’s tail (Hippuris vulgaris) were enriched with marine N only. Riparian vegetation (Sitka alder Alnus viridis ssp. sinuata and willow Salix spp.) did not show enrichment. Artificial additions of adult carcasses and eggs of coho salmon increased the δ¹⁵N and δ¹³C values of juvenile coho salmon. In this dynamic and hydrologically complex coastal environment, spawning coho salmon contributed marine N and C comprising 10–50% of the dietary needs of juvenile coho salmon through direct consumption of eggs and carcass material. Invertebrates that have assimilated marine N and C yield a further indirect contribution. This perennial subsidy maintains the productivity of the ecosystem of the coho salmon on the CRD.     

Using Bayesian stable isotope mixing models to estimate wolf diet in a multi-prey ecosystem

Stable isotope analysis (SIA) of wolf (Canis lupus) tissues can be used to estimate diet and intra-population diet variability when potential prey have distinct δ¹³C and δ¹⁵N values. We tested this technique using guard hairs collected from 44 wolves in 12 northwestern Montana packs, summer 2009. We used hierarchical Bayesian stable isotope mixing models to determine diet and scales of diet variation from δ¹³C and δ¹⁵N of wolves and potential prey, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), snowshoe hare (Lepus americanus), and other prey. As a check on SIA results, we conducted a separate diet analysis with temporally matched scats (i.e., collected in summer 2008) from 4 of the same packs. Wolves were centered on the ungulate prey in the isotope mixing space. Both methods revealed differences among pack diets and that wolves may consume moose in greater proportions than predicted by available biomass. Stable isotope analysis, and scat results were not entirely concordant; assumptions related to tissues of use in SIA, hair growth period in wolves, and scat sampling may have contributed to a mismatch between methods. Incorrect fractionation values, insufficient separation of prey in the isotope mixing space, choice of prior information in the Bayesian mixing models, and unexplained factors may have distorted diet estimates. However, the consistently high proportion of moose in pack diets suggests that increased population monitoring would benefit management of moose and wolves. Our results also support suggestions of other researchers that species-specific fractionation values should be used whenever possible, and that SIA may sometimes only provide indices of use for general groups of prey (e.g., large ungulates). © 2012 The Wildlife Society.     

The nitrogen supply from soils and insects during growth of the pitcher plants Nepenthes mirabilis, Cephalotus follicularis and Darlingtonia californica

This study investigated the nitrogen (N) acquisition from soil and insect capture during the growth of three species of pitcher plants, Nepenthes mirabilis, Cephalotus follicularis and Darlingtonia californica. ¹⁵N/¹⁴N natural abundance ratios (δ¹⁵N) of plants and pitchers of different age, non-carnivorous reference plants, and insect prey were used to estimate proportional contributions of insects to the N content of leaves and whole plants. Young Nepenthes leaves (phyllodes) carrying closed pitchers comprised major sinks for N and developed mainly from insect N captured elsewhere on the plant. Their δ¹⁵N values of up to 7.2‰ were higher than the average δ¹⁵N value of captured insects (mean δ¹⁵N value = 5.3‰). In leaves carrying old pitchers that are acting as a N source, the δ¹⁵N decreased to 3.0‰ indicating either an increasing contribution of soil N to those plant parts which in fact captured the insects or N gain from N₂ fixation by microorganisms which may exist in old pitchers. The δ¹⁵N value of N in water collected from old pitchers was 1.2‰ and contained free amino acids. The fraction of insect N in young and old pitchers and their associated leaves decreased from 1.0 to 0.3 mg g⁻¹. This fraction decreased further with the size of the investigated tiller. Nepenthes contained on average 61.5 ± 7.6% (mean ± SD, range 50–71%) insect N based on the N content of a whole tiller. In the absence of suitable non-carnivorous reference plants for Cephalotus, δ¹⁵N values were assessed across a developmental sequence from young plants lacking pitchers to large adults with up to 38 pitchers. The data indicated dependence on soil N until 4 pitchers had opened. Beyond that stage, plant size increased with the number of catching pitchers but the fraction of soil N remained high. Large Cephalotus plants were estimated to derive 26 ± 5.9% (mean ± SD of the three largest plants; range: 19–30%) of the N from insects. In Cephalotus we observed an increased δ¹⁵N value in sink versus source pitchers of about 1.2‰ on average. Source and sink pitchers of Darlingtonia had a similar δ¹⁵N value, but plant N in this species showed δ¹⁵N signals closer to that of insect N than in either Cephalotus or Nepenthes. Insect N contributed 76.4 ± 8.4% (range 57–90%) to total pitcher N content. The data suggest complex patterns of partitioning of insect and soil-derived N between source and sink regions in pitcher plants and possibly higher dependence on insect N than recorded elsewhere for Drosera species. Received: 14 April 1997 / Accepted: 18 August 1997     

Wolf predation on moose and roe deer: chase distances and outcome of encounters

We examined chase distances of gray wolves Canis lupus Linnaeus, 1758 hunting moose Alces alces and roe deer Capreolus capreolus, and recorded details of encounters between wolves and prey on the Scandinavian Peninsula, 1997–2003. In total, 252 wolf attacks on moose and 64 attacks on roe deer were registered during 4200 km of snow tracking in 28 wolf territories. Average chase distances were 76 m for moose and 237 m for roe deer, a difference likely due to variation in body size and vigilance between prey species. A model including prey species, outcome of the attack, and snow depth explained 15–19% of the variation found in chase distances, with shorter chase distances associated with greater snow depth and with successful attacks on moose but not on roe deer. Wolf hunting success did not differ between prey species (moose 43%, roe deer 47%) but in 11% of the wolf attacks on moose at least one moose was injured but not killed, whereas no injured roe deer survived. Compared with most North American wolf studies chase distances were shorter, hunting success was greater, and fewer moose made a stand when attacked by wolves in our study. Differences in wolf encounters with moose and roe deer likely result from different anti-predator behaviour and predator-prey history between prey species.     

Transit time and digestibility of two experimental diets in the maned wolf (Chrysocyon brachyurus) and domestic dog (Canis lupus)

Recent research involving nutritional management of clinical disease secondary to cystinuria in captive maned wolves (Chrysocyon brachyurus) in the United States resulted in the production of a commercially manufactured maintenance diet and subsequently, a further modified experimental diet. These two diets differed only in their protein sources and sodium concentrations. The purpose of this study was to further investigate these diets by determining their digestibility and transit time in maned wolves, and also to compare these results to the digestibility and transit time of the diets in domestic dogs. The experiment consisted of two diets (maned wolf commercial maintenance diet and experimental diet) and two species (maned wolf and domestic dog [beagle]) arranged as a 2 × 2 factorial design. For the transit time study, titanium dioxide (TiO₂, 5 g/kg diet) was administered as a pulse dose and total collection of feces was carried out for 50 hr. There was no effect of diet or species on initial Ti recovery time (IRT), the amount of Ti recovered at IRT, or the time to reach 50% of Ti excretion in the feces. Maned wolves had lower total percent recovery (P<0.01) of Ti than dogs and shorter time to last recovery of Ti in the feces (P<0.05), however, marker excretion in the maned wolves may not have been complete. For the digestibility study, in which chromic oxide was used as a marker, fecal samples were collected on 2 consecutive days immediately after 12 days of being fed the diets and then analyzed for dry matter, energy, protein, and minerals. Crude protein, calcium, phosphorus, and zinc apparent digestibilities were unaffected by species or diet (P>0.05). Apparent digestibility of dry matter (P<0.05) and energy (P<0.01) were higher in the experimental diet and in the dogs. Both dogs and maned wolves fed the maintenance diet exhibited a greater apparent retention of copper, iron, and magnesium (P<0.01). Dogs had a higher apparent retention of magnesium and sodium than the maned wolves. Zoo Biol 0:1–13, 2006. © 2006 Wiley‐Liss, Inc.     

Variations in leaf β13C along a vertical profile of irradiance in a temperate Japanese forest

The vertical profile of stable carbon isotope ratios (δ¹³C) of leaves was analyzed for 13 tree species in a cool-temperate deciduous forest in Japan. The vertical distribution of long-term averaged δ¹³C in atmospheric CO₂ (δ_a) was estimated from δ¹³C of dry matter from NADP-malic enzyme type C₄ plant (Zea mays L. var. saccharata Sturt.) grown at a tower in the forest for 32␣days, assuming constant Δ value (3.3‰) in Z. mays against height. The δ_a value obtained from δ¹³C in Z.␣mays was lowest at the forest floor (−9.30 ± 0.03‰), increased with height, and was almost constant above 10␣m (−7.14 ± 0.14‰). Then leaf Δ values for the tree species were calculated from tree leaf δ¹³ C andδ_a. Mean leaf Δ values for the three tall deciduous species (Fraxinus mandshurica, Ulmus davidiana, and Alnus hirsuta) were significantly different among three height levels in the forest: 23.1 ± 0.7‰ at the forest floor (understory), 21.4 ± 0.5‰ in lower canopy, and 20.5 ± 0.3‰ in upper canopy. The true difference in tree leaf Δ among the forest height levels might be even greater, because Δ in Z. mays probably increased with shading by up to ∼‰. The difference in tree leaf Δ among the forest height levels would be mainly due to decreasing intercellular CO₂ (C _i) with the increase in irradiance. Potential assimilation rate for the three tree species probably increased with height, since leaf nitrogen content on an area basis for these species also increased with height. However, the increase in stomatal conductance for these tree species would fail to meet the increase in potential assimilation rate, which might lead to increasing the degree of stomatal limitation in photosynthesis with height. Received: 30 September 1995 / Accepted: 25 October 1996     

Role of brown bears (Ursus arctos) in the flow of marine nitrogen into a terrestrial ecosystem

We quantified the amount, spatial distribution, and importance of salmon (Oncorhynchus spp.)-derived nitrogen (N) by brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. We tested and confirmed the hypothesis that the stable isotope signature (δ¹⁵N) of N in foliage of white spruce (Picea glauca) was inversely proportional to the distance from salmon-spawning streams (r=–0.99 and P<0.05 in two separate watersheds). Locations of radio-collared brown bears, relative to their distance from a stream, were highly correlated with δ¹⁵N depletion of foliage across the same gradient (r=–0.98 and –0.96 and P<0.05 in the same two separate watersheds). Mean rates of redistribution of salmon-derived N by adult female brown bears were 37.2±2.9 kg/year per bear (range 23.1–56.3), of which 96% (35.7±2.7 kg/year per bear) was excreted in urine, 3% (1.1±0.1 kg/year per bear) was excreted in feces, and <1% (0.3± 0.1 kg/year per bear) was retained in the body. On an area basis, salmon-N redistribution rates were as high as 5.1±0.7 mg/m² per year per bear within 500 m of the stream but dropped off greatly with increasing distance. We estimated that 15.5–17.8% of the total N in spruce foliage within 500 m of the stream was derived from salmon. Of that, bears had distributed 83–84%. Thus, brown bears can be an important vector of salmon-derived N into riparian ecosystems, but their effects are highly variable spatially and a function of bear density. Received: 11 February 1999 / Accepted: 7 July 1999     

Camera-trap studies of maned wolf density in the Cerrado and the Pantanal of Brazil

The maned wolf (Chrysocyon brachyurus) is threatened by large-scale habitat loss, in particular due to conversion to agricultural land. This is the first published study on maned wolf density and the first test of individual identification from camera-trap photographs. We present results from two Brazilian regions: the Cerrado and the Pantanal. Using capture–recapture analysis of camera-trap data, we estimated densities per 100 square kilometers of 3.64 ± 0.77 individuals at the Cerrado site and 1.56 ± 0.77 individuals at the Pantanal site. Parallel radio-telemetry studies at the Pantanal site showed that maned wolves occupied home ranges of 39–58 km² (mean = 50.3 ± 7.67 km²). Our study in the Cerrado took place in a private farm with a mixture of agricultural land and native habitats, representative of the majority of the present-day Cerrado. Whereas many other mammalian species have suffered in the region, our results show that the maned wolf may cope better with this highly fragmented landscape than one might have feared. Finally, the paper briefly compares maned wolf density with density of puma (Puma concolor) in the Pantanal site.     

Effect of manipulation of the renin-angiotensin system in control of drinking in juvenile Atlantic salmon (Salmosalar L) in fresh water and after transfer to sea water

Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at a rate of 0.15 ± 0.03 ml · kg⁻¹ · h⁻¹ and administration of doses of 10 or 20 mg · kg⁻¹ of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn¹, Val⁵]-Angiotensin II (0.4 μmol · kg⁻¹) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril (50 mg · kg⁻¹) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg⁻¹ · h⁻¹, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg⁻¹) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg⁻¹ lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg⁻¹ · h⁻¹, respectively. All treatments were without effect on blood plasma levels of Na⁺ and Cl⁻ in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na⁺ and Cl⁻. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed. Accepted: 27 February 1997     

Comparative analysis of the digestive efficiency and nitrogen and energy requirements of the phyllostomid fruit-bat (Artibeus jamaicensis) and the pteropodid fruit-bat (Rousettus aegyptiacus)

Nitrogen (N) and energy (E) requirements of the phyllostomid fruit bat, Artibeus jamaicensis, and the pteropodid fruit bat Rousettus aegyptiacus, were measured in adults that were fed on four experimental diets. Mean daily food intake by A. jamaicensis and R. aegyptiacus ranged from 1.1–1.6 times body mass and 0.8–1.0 times body mass, respectively. Dry matter digestibility and metabolizable E coefficient were high (81.1% and 82.4%, respectively) for A. jamaicensis and (77.5% and 78.0%, respectively) for R. aegyptiacus. Across the four diets, bats maintained constant body mass with mean metabolizable E intakes ranging from 1357.3 kJ · kg^−0.75 · day⁻¹ to 1767.3 kJ · kg^−0.75 · day⁻¹ for A. jamaicensis and 1282.6–1545.2 kJ · kg^−0.75 · day⁻¹ for R. aegyptiacus. Maintenance E costs were high, in the order of 3.6–5.4 times the basal metabolic rate (BMR). It is unlikely that the E intakes that we observed represent a true measure of maintenance E requirements. All evidence seems to indicate that fruit bats are E maximizers, ingesting more E than required and regulating storage by adjusting metabolic output. We suggest that true maintenance E requirements are substantially lower than what we observed. If it follows the eutherian norm of two times the BMR, fruit bats must necessarily over-ingest E on low-N fruit diet. Dietary E content did affect N metabolism of A. jamaicensis. On respective low- and high-E diets, metabolic fecal N were 0.492 mg N · g⁻¹ and 0.756 mg N · g⁻¹ dry matter intake and endogenous urinary N losses were 163.31 mg N · kg^−0.75 · day⁻¹ and 71.54 mg N · kg^−0.75 · day⁻¹. A. jamaicensis required 332.3 mg · kg^−0.75 · day⁻¹ and 885.3 mg · kg^−0.75 · day⁻¹ of total N on high- and low-E diets, respectively, and 213.7 mg · kg^−0.75 · day⁻¹ of truly digestible N to achieve N balance. True N digestibilities were low (29% and 49%) for low- and high-E diets, respectively. For R. aegyptiacus, metabolic fecal N and endogenous urinary N losses were 1.27 mg N · g⁻¹ dry matter intake and 96.0 mg N · kg^−0.75 · day⁻¹, respectively, and bats required 529.8 mg · kg^−0.75 · day⁻¹ (total N) or 284.0 mg · kg^−0.75 · day⁻¹ (truly digestible N). True N digestibility was relatively low (50%). Based on direct comparison, we found no evidence that R. aegyptiacus exhibits a greater degree of specialization in digestive function and N retention than A. jamaicensis. When combined with results from previous studies, our results indicate that all fruit bats appear to be specialized in their ability to retain N when faced with low N diet. Accepted: 24 November 1998     

Food requirements of breeding king penguins at Heard Island and potential overlap with commercial fisheries

The diet composition of king penguins (Aptenodytes patagonicus) at Heard Island (53°05′S; 73°30′E) was determined from stomach contents of 98 adults captured as they returned to the island throughout 1992. During the two growth seasons, the diet was dominated by the myctophid fish Krefftichthys anderssoni (94% by number, 48% by mass). The paralepidid fish Magnisudis prionosa contributed <1% by numbers but 17% by mass. Mackerel icefish (Champsocephalus gunnari) accounted for 17% by mass of chick diet in late winter, when chicks were malnourished and prone to starvation, although its annual contribution to the penguins' diet was only 3%. Squid was consumed only between April and August; Martialia hyadesi was the commonest squid taken, comprising 40–48% of the winter diet. The remainder of the diet consisted of the squid Moroteuthis ingens and fish other than K. anderssoni. The energy content of the diet mix fed to the chicks varied seasonally being highest during the growth seasons (7.83 ± 0.25 kJ g⁻¹) and lowest in winter (6.58 ± 0.19 kJ g⁻¹). From energetic experiments we estimated that an adult penguin consumed 300 kg of food each, of which its chick received 55 kg during the 1992 season. The chicks received large meals at the beginning of winter (1.2 ± 0.3 kg) and during the middle of the second growth season (1.2 ± 0.3 kg), and their smallest meals in late winter (0.4 ± 0.1 kg). The gross energy required to rear a king penguin chick was estimated to be 724 MJ. The potential impact of commercial fisheries on the breeding activities of king penguins is discussed. Received: 20 October 1997 / Accepted: 27 April 1998     

Influence of stand structure on carbon-13 of vegetation, soils, and canopy air within deciduous and evergreen forests in Utah, United States

Carbon isotope ratios (δ¹³C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah (Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during two consecutive growing seasons. The δ¹³C_leaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ¹³C_leaf values (increasing carbon isotope discrimination) with increasing LAI. The δ¹³C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ¹³C_leaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c _i/c _a (> 60%) and to a minor extent due to δ¹³C of canopy air (< 40%). This intra-canopy depletion of δ¹³C_leaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ¹³C_leaf did not change with canopy LAI, δ¹³C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ¹³C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate forests. The δ¹³C_canopy of CO₂ in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ¹³C_canopy, and [CO₂]_canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δ_e) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ¹³C_canopy and [CO₂]_canopy were larger in denser Acer spp. stands than those in the open stand. However, ¹³C enrichment above and photosynthetic draw-down of [CO₂]_canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory vegetation. Seasonal patterns of the relationship δ¹³C_canopy versus 1/[CO₂]_canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δ_e for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However, Δ_e varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰). Received: 15 April 1996 / Accepted: 19 October 1996     

Comparison of Mexican Wolf and Coyote Diets in Arizona and New Mexico

ABSTRACT Interactions between wolves (Canis lupus) and coyotes (C. latrans) can have significant impacts on their distribution and abundance. We compared diets of recently translocated Mexican wolves (C. l. baileyi) with diets of resident coyotes in Arizona and New Mexico, USA. We systematically collected scats during 2000 and 2001. Coyote diet was composed mostly of mammalian species, followed by vegetation and insects. Elk (Cervus elaphus) was the most common item in coyote scats. Mexican wolf diet had a higher proportion of large mammals and fewer small mammals than coyote diet; however, elk was also the most common food item in Mexican wolf scats. Our results suggest that Mexican wolf diet was more similar to coyote diet than previously reported, but coyotes had more seasonal variation. Considering results in other areas, we expect that Mexican wolves will have a negative impact on coyotes through direct mortality and possibly competition. Reintroduction of Mexican wolves may have great impacts on communities by changing relationships among other predators and their prey.     

Activity patterns of gray wolves housed in small vs. large enclosures

Free-ranging gray wolves (Canis lupus) generally inhabit large home ranges, yet they are housed in a variety of restricted spaces when in captivity. There is continual debate as to whether space restrictions alter a wolf's behavior. The purpose of these studies was to remotely measure and then compare the amount and frequency of activity of gray wolves housed in small, artificial enclosures vs. large, more natural enclosures. Test animals comprised three adult wolves housed in kennels and three and four wolves housed in separate natural enclosures. Kenneled wolves had 2.8 m² of surface area per wolf, and wolves in natural enclosures had 466.6 m² (South Pack) and 349.9 m² (North Pack) per wolf. Wolves were fitted with radiotelemetry collars containing activity sensors. Activity data were recorded every 20 min for 57 continuous hr. The amount of activity for each wolf was calculated using areas under the curve (AUCs), and the frequency of activity was analyzed by spectral analysis. There was no difference (P ≥ 0.22) in AUCs between kenneled wolves (1.399 ± 0.214 x 10⁵ radians) and South Pack wolves (1.564 ± 0.139 X 10⁵ radians) or North Pack wolves (1.617 ± 0.192 x 10⁵ radians). All three groups had similar peak spectral values at frequencies that were close to daily cycles (i.e., ω = 0.12–0.17 cycles per unit time). Peaks in coherence near the dominant spectral frequency were most significant between the natural enclosures and the least significant between the kenneled wolves and the South Pack wolves. Based on these criteria of activity and under these circumstances, enclosure size appeared to have no effect on wolf activity. However, small sample sizes and variation in the data do not make these results definitive. © 1996 Wiley-Liss, Inc.