Comparative use of four different marker systems for the estimation of digestibility and low food intake in a group of captive giraffes (Giraffa camelopardalis)

In a feeding trial with four captive giraffes, nutrient digestibility was determined using four different marker systems. Although cobalt‐ethylenediaminetetraacetic acid proved to have no utility as a digestibility marker in this study, reasonable values could be obtained using C₃₆ n‐alkane, acid detergent lignin, and acid insoluble ash as markers. A comparison of methods and literature data suggests that the values derived from the C₃₆ n‐alkane assay are the most reliable absolute values. Apparent digestibility ranges thus determined were 63.5–74.3% for dry matter, 73.4–82.4% for crude protein, 49.9–62.2% for neutral detergent fiber, and 49.7–63.7% for acid detergent fiber. However, digestibility data gained by the ADL method provided the most stringent inter‐individual comparisons. It is concluded that both alkanes and lignin can be used for giraffe digestibility studies. These captive giraffes ingested a smaller quantity of food than has been reported for other giraffes from both the wild and other zoos. Energetic calculations showed that these animals might be on the brink of an energy deficit. A similar situation has been described at least once before in captive giraffes, and the results are of direct relevance to the peracute mortality syndrome, a condition of captive giraffes in which severe depletion of body fat stores occurs. Reasons for the seemingly low food intake could not be elucidated, but observations suggested that these giraffes were ready to ingest more if more palatable or suitable food was offered. Monitoring food intake in other giraffe groups and designing a diet that is both palatable and nutritious are important objectives of captive giraffe management. Zoo Biol 20:315–329, 2001. © 2001 Wiley‐Liss, Inc.     

青藏高原高寒草甸门源草原毛虫取食偏好及其与植物C、N含量的关系

草食性昆虫对不同植物物种的取食存在偏好,这种取食偏好可能受其自身对蛋白质和碳水化合物的需求及二者平衡的调节。以青藏高原高寒矮嵩草草甸31种常见植物及门源草原毛虫为对象,通过饲喂实验,研究了草食性昆虫对不同物种和不同功能群植物的取食偏好,及其与植物叶片C、N含量和C∶N之间的关系。在31种植物中,门源草原毛虫对19种植物进行了取食,尤其对矮嵩草、红棕薹草、藏异燕麦和垂穗披碱草四种植物表现出强烈的取食偏好,而对另外12种植物未进行任何取食。在物种水平上,门源草原毛虫取食量与植物叶片N含量呈显著负相关,与叶片C∶N呈正相关。从功能群水平上看,门源草原毛虫对莎草类的取食偏好最大,而对豆科植物取食偏好最低;相应地,莎草类植物叶片N含量最低、C∶N最高,而豆科植物叶片N含量最高、C∶N最低。因此,即使在土壤有效氮匮乏、植物生长受氮素限制的高寒草甸生态系统,植物体内N含量的增加也可能不利于草食性昆虫的取食。门源草原毛虫对优势植物矮嵩草和垂穗披碱草的取食对高寒矮嵩草草甸物种共存和生物多样性维持可能具有重要的作用。     

Sub-alpine amphibian distributions related to species palatability to non-native salmonids in the Klamath mountains of northern California

The goal of this study was to examine how introduced trout influence the distributions and abundances of a sub‐alpine amphibian assemblage whose members display a variety of different life‐history and defence strategies. Our study was conducted in the sub‐alpine lentic habitats of three wilderness areas that form the core of the Klamath‐Siskiyou Bioregion of northern California, a biodiversity ‘hotspot’ that supports the highest diversity of sub‐alpine, lentic‐breeding amphibians in the western USA. These wilderness areas contain no native fishes, but all have been populated with non‐native trout for recreational fishing. Five of the eight amphibian species that occur in this region were sufficiently common to use in our study; these included one that breeds in both temporary and permanent waters and is palatable to fish (Pacific treefrog, Pseudacris regilla), two that breed primarily in permanent waters and are unpalatable to fish (western toad, Bufo boreas, and rough‐skinned newt, Taricha granulosa), and two that breed primarily in permanent waters and are palatable to fish (Cascades frog, Rana cascadae, and long‐toed salamander, Ambystoma macrodactylum). Based on life histories and predator defence strategies (i.e. palatable or not), we predicted that the three palatable species would likely be negatively correlated with introduced trout, but with P. regilla less impacted because of its use of both temporary and permanent waters. We predicted that B. boreas and T. granulosa would not be significantly correlated with introduced trout due to the lack of any predator/prey interactions between them. We surveyed 728 pond, lake, or wet meadow sites during the summers of 1999–2002, using timed gill‐net sets to measure trout occurrence and relative density, and visual encounter surveys to determine amphibian presence and abundance. We used semiparametric logistic regression models to quantify the effect of trout presence/absence and density on the probability of finding amphibian species in a water body while accounting for variation within and among the various lentic habitats sampled. The distributions of P. regilla, A. macrodactylum and R. cascadae were strongly negatively correlated with trout presence across all three wilderness areas. Ambystoma macrodactylum was 44 times more likely to be found in lakes without fish than in lakes with fish. Rana cascadae and P. regilla were 3.7 and 3.0 times more likely, respectively, to be found in fishless than fish‐containing waters. In contrast, the two unpalatable species were either uncorrelated (T. granulosa) or positively correlated (B. boreas) with fish presence. We found that the relative density of fish (catch per unit effort) was negatively correlated with the combined abundances of the three palatable amphibians, and also with both the length and the condition of the fish themselves. Our results are consistent with a compelling body of evidence that introduced fishes greatly alter the aquatic community structure of mountain lakes, ponds, and wet meadows.     

Are European White Butterflies Aposematic?

It has been suggested that the white coloration of Pieridae butterflies is a warning signal and therefore all white Pieridae could profit from a mimetic resemblance. We tested whether green-veined white (Pieris napi) and orange-tip (Anthocharis cardamines) butterflies benefit from white coloration. We compared their relative acceptability to wild, adult pied flycatchers (Ficedula hypoleuca) by offering live A. cardamines and P. napi together with two non-aposematic butterflies on the tray attached to birds' nesting boxes. Experienced predators equally attacked white and non-white butterflies, and the order of attack among the Pieridae was random. If anything, there was a slight indication that the female A. cardamines was the least favoured prey. Since birds did not avoid white coloration, we compared the palatability of these two species against known palatable and unpalatable butterflies by presenting them to great tits (Parus major). Pieris brassicae, which has been earlier described as unpalatable, was also included in the palatability test. However, there were no significant differences in the palatability of the butterflies to birds, and even P. brassicae was apparently palatable to the great tits. Our results do not unambiguously support the hypothesis that the white coloration of Pieridae would signal unpalatability. Nevertheless, in our last experiment, pied flycatchers often rejected or left untouched free flying P. napi and A. cardamines. This suggests that other features in a more natural situation, such as the agile flight pattern or odours might still make them unprofitable to birds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of food plant and group size on predator defence: differences between two co-occurring aposematic Lygaeinae bugs

1. The role of food plant and aggregation on the defensive properties of two aposematic sympatrically occurring seed bugs, Tropidothorax leucopterus and Lygaeus equestris (Lygaeinae, Heteroptera), was investigated. Larvae reared on seeds either of their natural host plant Vincetoxicum hirundinaria (Asclepiadaceae) or of sunflower Helianthus annuus were subjected to predation by chicks. 2. The two species differ in their dependency on the host for their defence. Lygaeus equestris was better defended on its natural host plant than on the alternative food, as indicated by fewer attacks, lower mortality, and predator avoidance after experience. No such effect of food plant could be found for T. leucopterus, suggesting the existence of alternative defences in this species. 3. The number of attacks was lower when host plant‐fed larvae of both species were presented in groups. 4. The discussion concerns how major components of an aposematic syndrome, such as host plant chemistry, insect colouration, and aggregation, are integrated with other life‐history traits to form alternative lifestyles in L. equestris and T. leucopterus.     

Palatability of Thlaspi caerulescens for snails: influence of zinc and glucosinolates

* The hypothesis that zinc (Zn) hyperaccumulation defends Thlaspi caerulescens against herbivores is tested with the snail Helix aspersa. We investigated the effects of leaf zinc, cadmium, glucosinolate, nitrogen and dry matter concentrations on the feeding preferences of snails. * Four T. caerulescens populations from southern France (two from metalliferous and two from normal soils) were grown on low- and high-Zn soils to obtain contrasting leaf Zn concentrations. Plants were also collected in the field, and binary feeding choices involving low- and high-Zn leaves were conducted. * Foliar Zn, Cd, N and dry matter concentrations did not affect the feeding choices of snails, whereas glucosinolate had a significant negative effect on herbivore preferences. Compared with metallicolous plants, nonmetallicolous ones appeared to be better protected against snails, whatever their Zn concentration. * These results do not support the defence hypothesis, as glucosinolates appear to decrease the degree of herbivory when Zn does not.     

Seasonal variations in the quality of mopane leaves as a source of browse for mammalian herbivores

This paper deals with seasonal variations in the chemical composition of mopane leaves in terms of their palatability to herbivores. Green mopane leaves were found to be most palatable over summer, a period when, due to very poor rainfall, the veld was at its most desolate. Senescing leaves were at their most palatable in late winter/early spring, this resource maintaining many herbivores for the short period before the spring leaf flush. Four leaf classes were identified during the spring leaf flush: young green leaves were the most palatable followed by very young leaves, mature green leaves and senescent leaves. The flush is independent of rain and coincides with the end of the dry season, a period when most tree species occurring in association with the mopane are leafless and the grass sward is very poor. It begins earlier on heavily browsed trees. Most ungulates present in the area were found to utilize the nutritious young leaves. The importance of this leaf flush is discussed with respect to the management of the area, and the importance of the heavy pressure large mammals are imposing on this veld type is elicited.     

Avoidance of unpalatable prey by predaceous diving beetle larvae: The role of hunger level and experience (Coleoptera: Dytiscidae)

The effects of hunger and experience on the avoidance of unpalatable prey were examined. Larvae of the predaceous diving beetle,Dytiscus verticalis, after feeding on one of two feeding regimes, were offered palatable and unpalatable prey during a series of trials. Consumption of palatable prey (calf heart) was not affected by hunger or experience. Avoidance of unpalatable prey (tails of the red-spotted newtNotophthalmus viridescens) decreased with increased hunger, with hungrier predators sampling unpalatable prey more often. Although the overall level of avoidance varied across trials, the degree of difference in avoidance between predators at different hunger levels remained relatively constant across trials. Beetle larvae responded to an increase in their feeding regime within 36 h (after two trials), by becoming more selective. In a separate experiment, hunger level affected the number of beetle larvae that seized unpalatable newt tails, but experience did not.     

Chemical composition of pods and seeds of Dichrostachys cinerea as a basis of seed dispersal

The occurrence of very few seeds of Dichrostachys cinerea in the soil seed bank prompted the present study as to why animal browsers and seed predators should select the infructescence of this plant. The preferential and extensive browsing of this indehiscent legume is apparently not due to any exceptional nutritive value of the pods and seeds. However, it is probably the strong rich aroma of the infructescence which initially attracts animals to this food source. The structure of the infructescence, ensures that upon location a large number of pods and seeds are consumed. Ingestion of the pods will provide fibre, lipid, fatty acids, carbohydrates, amino acids, nitrogen and protein.