Susan M. Cooper

Effects of plant spinescence on large mammalian herbivores

SummaryPlant thorns and spines had these effects on the feeding behaviour of the three species of browsing ungulate that we studied, kudu, impala and domestic goats: (i) bite sizes were restricted, in most cases to single leaves or leaf clusters; (ii) hooked thorns retarded biting rates; (iii) the acceptability of those plant species offering small leaf size in conjunction with prickles was lower, at least for the kudus, than those of other palatable plant species; (iv) the inhibitory effect of prickles on feeding was much less for the smaller impalas and goats than for the larger kudus; (v) from certain hook-thorned species the kudus bit off shoot ends despite their prickles; (vi) for certain straight-thorned species the kudus compensated partially for the slow eating rates obtained by extending their feeding durations per encounter. Most spinescent species were similar in their acceptability to the ungulates to unarmed palatable species, despite higher crude protein contents in their foliage than the latter. Such structural features furthermore reduce the tissue losses incurred by plants per encounter by a large ungulate herbivore, by restricting the eating rates that the animals obtain. In this way prickles function to restrict foliage losses to large herbivores below the levels that might otherwise occur.

Condensed tannins deter feeding by browsing ruminants in a South African savanna

SummaryThe palatability of 14 species of woody plant was assessed for three species of browsing ruminant, namely kudus, impalas and goats. Results show that palatability was most clearly related to leaf contents of condensed tannins. The effect was a threshold one, with all plants containing more than 5% condensed tannins being rejected as food during the wet season period. In contrast palatability was not influenced by concentrations of protein-precipitating polyphenols, and only weakly related to contents of nitrogen, phosphorus, cations, fibre components and other secondary metabolites. Insect herbivory shows a different pattern. These findings support the hypotheses that (i) condensed tannins function to protect plant cell walls against microbial attack; (ii) hydrolyzable tannins function to inactivate the digestive enzymes of insect herbivores. Large mammalian herbivores are influenced by condensed tannins due to their dependance upon microbial fermentation of plant cell walls for part of their energy needs.

Palatability of Woody Plants to Browsing Ruminants in a South African Savanna

We recorded food selection by free-ranging kudus (Tragelaphus strepsiceros), impalas (Aepyceros melampus), and domestic goats in the Nylsvley Nature Reserve in South Africa. The predominant vegetation is a deciduous wooded savanna growing on infertile sandy soils; patches of Acacia savanna occur on the more fertile sites of former human settlements. Woody species fall into two basic categories of acceptability to the animals: (1) species favored year-round; and (2) species generally rejected, except during certain periods. Among the latter, some species increase in acceptability during the dry season; others are favored temporarily while new leaves predominate. Some species remain low in acceptability year-round. We propose a palatability classification of woody species, considering features of leaf retention (deciduous vs. evergreen) and spinescence, as well as seasonal variations in acceptability. Estimated annual foliage losses to browsing ungulates were 1-3% for unpalatable deciduous species, compared with 10-30% for most palatable unarmed deciduous and evergreen species. Unpalatable deciduous species dominate the woody foliage biomass on the infertile soils, while palatable but spinescent species make up most of the leaf biomass of trees and shrubs on the more fertile sites. These patterns seem widely typical of African savanna. Plants known to have chemical defenses against vertebrate herbivory are prominent on nutrient-deficient soils, while those with structural defenses are prominent on fertile soils.

Foliage acceptability to browsing ruminants in relation to seasonal changes in the leaf chemistry of woody plants in a South African savanna

SummaryWe investigated seasonal changes in food selection by hand-reared kudus and impalas in savanna vegetation in northern Transvaal, South Africa. The acceptability of the leaves of woody plants to these animals was compared with leaf concentrations of nutrients, fibre components and old leaf phenophases. No consistently significant correlation was found between acceptability and any single chemical factor. Based on an a priori palatability classification, discriminant function analysis separated relatively palatable species from unpalatable species in terms of a linear combination of protein and condensed tannin concentrations. The high acceptability of certain otherwise unpalatable species during the new leaf phenophase was related to elevation of protein levels relative to condensed tannin contents. Species were added to the diet during the dry season approximately in the order of their relative protein-condensed tannin difference.

Patterns of Association among Female Spotted Hyenas (Crocuta crocuta)

We examined subgroup association patterns among adult female members of a clan of free-living spotted hyenas ( Crocuta crocuta ) and between adult females and their juvenile offspring during three consecutive stages of development of offspring. These stages represented the approximate periods of residence of offspring at the communal den, from 1 to 8 months of age, between leaving the communal den and weaning, from 8 to 14 months, and between weaning and reproductive maturity or dispersal, from 14 to 36 months of age. Mean association indices among adult female dyads varied with social rank, with the highest mean association index observed for the alpha female. Adult females associated more closely with their adult female kin than with unrelated adult females. Female kin from high-ranking matrilines associated more closely than did kin from lower-ranking matrilines. Within mother-offspring pairs, association patterns were strongly influenced by the mothers social rank during all three stages of development of offspring, with high-ranking mother-offspring dyads associating more tightly than low-ranking dyads at each stage. Mean mother-offspring association indices declined as offspring grew older, but we found no significant differences based on sex of offspring during any of the developmental stages examined.

Assessing food preferences of ungulates by acceptability indices

We assessed the preferences of greater kudus (Tragelaphus strepsiceros) for different woody plant species using acceptance or rejection frequencies, feeding durations, and forage ratios. We recorded the foraging behavior of hand-reared kudus in a 213-ha enclosure containing natural savanna vegetation in the Nylsvley Nature Reserve, South Africa. Plant-based acceptance was based on plants within neck reach of the animal during 1-hour observation sessions. Site-based acceptance was based on the presence of a species within readily visible range of the animal in 30-minute periods during all-day observations. Sitebased acceptances revealed a categorical distinction between favored and neglected plant species. Feeding durations were longer on high-acceptability species than on low-acceptability species. Plant-based acceptances showed a less clearcut pattern, due to statistical problems of interdependence between successive plants of the same species encountered. Forage ratios were subject to sampling errors in estimating the abundance and dietary proportions of less common plant species, especially where these were clumped in distribution. Rank orders of preference had little consistency, as species within the favored and neglected categories did not differ significantly in acceptability. Advantages of the site-based acceptability index include use of simple binomial statistics for confidence ranges and the elimination of time-consuming vegetation surveys to estimate abundance. J. WILDL. MANAGE. 51(2):372-378 To classify plant species in terms of their value as food resources for large herbivores some measure of relative preferences for them is required. The most widely used index is the forage ratio (FR) (Ivlev 1961, Petrides 1975). This is calculated by dividing the relative abundance of a food in the diet by its relative abundance in the environment. Foods that yield a ratio >1 are assumed to be positively selected (preferred or favored). Those that yield a ratio <1 are regarded as selected against (rejected or neglected). The FR has several shortcomings: it varies asymmetrically between 0 and infinity, confidence limits are not simply estimated, and conclusions about whether particular foods are positively or negatively selected depend upon the set of food types that the investigator deems to be available to the animal. Accordingly, various modifications of the simple FR have been proposed. The electivity index of Ivlev (1961) achieved a range of variation between limits of +1 and -1. The alpha index of Chesson (1978, 1983), and Vanderploeg and Scavias (1979) E*, are uninfluenced by changes in the number of food types considered available, or the abundance of these foods. Lechowicz (1982) reviewed the numerical behavior of these and other selection indices. To circumvent difficulties in deciding what food types were available, Johnson (1980) suggested that the rank orders of usage and availability be compared. Our study assessed the relative preferences of kudus for different woody plant species in a South African savanna. We present the results obtained from 2 acceptability indices that we derived, and compare them with other preference measures, including durations of feeding events and the forage ratio. Our study was carried out with the support of the Found. Res. Dev. of the Counc. Sci. and Ind. Res., and formed part of the S. Afr. Savanna Ecosystem Proj.

Spines protect plants against browsing by small climbing mammals

Abstract The presence of spines on woody plants has been shown to limit the loss of foliage to large mammalian browsers by restricting both bite size and biting rate. We tested the hypothesis that plant spines are also an effective defense against browsing by small mammals, such as rodents, that climb within the canopy of shrubs to harvest fruits, seeds, and foliage. Tame southern plains woodrats (Neotoma micropus) were allowed to harvest raisins impaled on the branches of blackbrush shrubs (Acacia rigidula Benth.) in five categories of spinescence: naturally spineless, moderately spiny, or very spiny branches, and moderately spiny and very spiny branches with the spines removed. Plant spinescence significantly reduced the woodrats foraging efficiency (P = 0.0001). Although plant spines are generally thought to be an evolved defense against browsing by ungulate herbivores, they may also reduce browsing by small mammals.

The Nutritional, Ecological, and Ethical Arguments Against Baiting and Feeding White-Tailed Deer

Abstract The use of food plots, supplemental feeding, and baiting has been a common and legal practice in Texas for many years. There is now controversy as to whether Texas Parks and Wildlife Department should include this extra nutrition as part of their carrying capacity estimates used to determine harvest permits for private landowners. Managers should remember that nutrition is only one component of carrying capacity, which includes water, shelter, and space as well. Extensive data exists about the potential negative impact of feeding on deer. Studies in Texas (Murden and Risenhoover 1993) have shown that fed deer (Odocoileus virginianus) can degrade rangeland by overconsuming high-quality plants and underconsuming low-quality plants. Guiterrez (1999) did not find that effect when South Texas deer were offered winter food plots. Donier et al. (1997) found in Minnesota that winter supplementation increased browse pressure within 900 m of feeders. Other reports (Williamson 2000) show increased browse pressure within a 1-mile radius of feeders, perhaps due to concentration of deer. Cooper et al. (2002) found 50% kernal home range sizes of fed deer were half that of unfed deer and that browse pressure near the feeder was 7 times that of unfed deer. Supplemental feeding has been suspected of contributing to the spread of tuberculosis in deer, chronic wasting disease in elk (Cervus canadensis) and deer, and brucellosis in elk and bison (Bison bison; Williamson 2000). Crowding due to supplemental feeding led to fighting and injuries in Michigan deer (Ozoga 1972). Feeding has actually led to starvation in deer due to increases in population when feeding was initiated (McCullough 1977, Schmitz 1990). Supplemental feed is consumed by nontarget species, possibly leading them to pass disease and to attract predators. Cooper and Ginnett (2000) found decreased survivorship of simulated turkey nests within 400 m of deer feeders in Texas. In 1998 we found illegal levels of aflatoxin in 40% of 100 randomly purchased bags of “deer corn” in Texas (N. Wilkins, Texas Cooperative Extension, USA, unpublished data). The ecological significance of deer feeding and baiting is only part of the issue. Feeding leads to ethical questions as well. Feeding is part of the domestication process, along with fencing, breeding, and health programs that, due to their expense, may lead to the desire for private ownership of wildlife. Baiting, likewise, adds to the advantages of the hunter over the hunted and may decrease hunter satisfaction and increase concerns of the antihunters and the nonhunting public (Ortega y Gasset 1995). Deer managers and agency personnel should review the data presented here and incorporate it into their decision making when considering feeding or baiting of deer.

Taphonomic and zooarchaeological implications of spotted hyena (Crocuta crocuta) bone accumulations in Kenya: a modern behavioral ecological approach

Abstract The significant impact of extant carnivores, particularly spotted hyenas, on the depositional history and physical characteristics of archaeofaunal and paleontological assemblages is well recognized. We focus on the behavioral ecology of extant spotted hyenas (Crocuta crocuta) in relation to bone accumulations produced by one East African clan at communal dens. Limbs and skulls of prey animals more frequently appear at dens than do other carcass portions. These items reflect the relative abundance of prey species near dens; carnivore remains are poorly represented. Comparative analysis reveals that bones are deposited far more slowly (<7 carcass portions per month) and accumulations tend to be smaller at Crocuta dens than at dens of either brown (Parahyaena brunnea) or striped (Hyaena hyaena) hyenas. We propose that extant Crocuta bone accumulation rates and sizes are likely affected by prey species abundance, clan size, social interactions within the clan, and the type and availability of den sites. We also suggest that the potential for intraspecific behavioral variability in bone accumulation patterns is important when comparisons are made among spotted hyena populations and across hyena species. For example, accumulation patterns may be dramatically influenced by the temporal span, potentially ranging from days to hundreds or thousands of years, in which bones are collected, depending on the species-specific history of occupation at a given site. Understanding the behavioral and ecological variability likely to influence bone accumulation patterns at dens used by different hyaenids will allow taphonomists and zooarchaeologists to refine their knowledge of mechanisms underlying site formation processes and potential causes of variability in deeper-time den assemblages.

Distribution and interspecies contact of feral swine and cattle on rangeland in south Texas: implications for disease transmission.

The last outbreak of foot-and-mouth disease (FMD) in the United States occurred in 1929. Since that time, numbers and distribution of feral swine (Sus scrofa) have increased greatly, especially in the southern states. This creates a potential risk to livestock production because swine are susceptible to, and can be carriers of, several economically harmful diseases of livestock. Most importantly, swine are potent amplifiers of FMD virus. In this study, global positioning system (GPS) collars were placed on rangeland cattle (Bos indicus × taurus) and feral swine to determine shared habitat use by these species on a large ranch in south Texas from 2004 to 2006. The aim was to identify locations and rates of interspecies contact that may result in effective transfer of FMD virus, should an outbreak occur. In shrubland and riparian areas, animals were dispersed, so contacts within and between species were relatively infrequent. Indirect contacts, whereby cattle and feral swine used the same location (within 20 m) within a 360-min period, occurred primarily at water sources, and seasonally in irrigated forage fields and along ranch roads. Direct contacts between species (animals <20 m apart and within 15 min) were rare and occurred primarily at water sources. Changes in ranch management practices are suggested to reduce interspecies contact should an FMD disease outbreak occur. This information can also be used to improve current epidemiologic models to better fit free-ranging animal populations.