Testing Predictions of the Prey of Lion Derived From Modeled Prey Preferences

Abstract: Apex predators are often threatened with extinction, and reintroduction is one method conservation managers are using to secure their persistence. Yet the ability to predict what these predators will eat upon reintroduction is lacking. Here we test predictions of the diet of the lion (Panthera leo), derived from dietary electivity index and optimality theory, using independent data collected from reintroduced and resident populations. We solved the Jacobs’ index preference equation for each prey species of the lion using values calculated by Hayward and Kerley (2005) and prey abundance data from 4 reintroduction sites and one resident lion population over several years. We then compared these estimates with actual kill data gathered from each site and time period, using the log-likelihood ratio and linear regression. The model precisely predicted the observed number of kills in 9 of the 13 tests. There was a highly significant linear relationship between the number of lion kills predicted to occur at a site and the number observed for all but one site (x̄r² = 0.612; β = 1.03). Predicting predator diet will allow conservation managers to stop responding and start planning in advance for reintroductions and environmental variation. Furthermore, ensuring that sufficient food resources are available is likely to increase the success of reintroduction projects. In addition, managers responsible for threatened prey species will be able to predict the vulnerability of these species to predation in the event of predator reintroductions or changes in abundance. These methods are applicable to virtually all large predators that have been sufficiently studied.     

African Elephants Loxodonta africana Amplify Browse Heterogeneity in African Savanna

There is a growing concern that the feeding habits of the African elephant, which include pushing over, uprooting and snapping trees, may have a negative impact on other herbivores. Browsed trees are known to respond by either increasing production (shoots and leaves) or defence (secondary compounds). It is not clear, however, what proportion of the browsed biomass can be made available at lower feeding heights after a tree is pushed over or snapped; thus, it is also unclear how the forage quality is affected. In a field survey in Kruger National Park, South Africa, 708 Mopane trees were measured over four elephant utilization categories: snapped trees, pushed‐over trees, uprooted trees and control trees. The elephants' impact on the leaf biomass distribution was quantified, and the forage quality (Ca, P, K and Mg, N, digestibility and condensed tannin [CT] concentrations) were analyzed. Pushed‐over and uprooted trees had the maximum leaf biomass at lower heights (<1 m), snapped trees at medium heights (1–2 m) and control trees at higher heights (>2 m). In all three utilization categories, the minimum leaf biomass was seven times higher than it was for control trees at a height of below 1 m. Leaf nitrogen content increased in all three categories and was significantly higher in snapped trees. CT concentrations increased slightly in all trees that were utilized by elephants, especially on granitic soils in the dry season. The results provide the insight that elephants facilitate the redistribution and availability of browse and improve the quality, which may positively affect small browsing herbivores.     

Prey Preference of Aphidoletes Aphidimyza on Acyrthosiphon Pisum: Effect of Prey Color and Size

Color polymorphism in insects as well as factors contributing to its occurrence and maintenance have been of a great interest. Pea aphid (A. pisum) exhibits a noteworthy color polymorphism which occurs as red and green. The preference of the predatory gall midge Aphidoletes aphidimyza (Rondani) for the two color morphs of pea aphid at two life stages (adult and second instar) was investigated. Red adults, red nymphs, green adults, and green nymphs were offered to the larvae of the predator in different sets. The larvae attacked red aphids more than green ones of a same size. But whenever adults were offered along with nymphs, the nymphs experienced significantly more attacks. Although visual cues could result in more predation on red aphids, our findings showed that the size of aphids was the more important factor. The results showed that previous findings, suggesting more predation on the red morph, are valid when the same size of aphids is used. The ovipositing females exhibited no differences in oviposition choice between stalks infested with either of two colors.     

Browsing-induced Effects on Leaf Litter Quality and Decomposition in a Southern African Savanna

We investigated the linkages between leaf litter quality and decomposability in a savanna plant community dominated by palatable-spinescent tree species. We measured: (1) leaf litter decomposability across five woody species that differ in leaf chemistry; (2) mass decomposition, nitrogen (N); and carbon (C) dynamics in leaf litter of a staple browse species (Acacia nigrescens) as well as (3) variation in litter composition across six sites that experienced very different histories of attack from large herbivores. All decomposition trials included litter bags filled with chopped straw to control for variation in site effects. We found a positive relationship between litter quality and decomposability, but we also found that Acacia and straw litter mass remaining did not significantly vary between heavily and lightly browsed sites. This is despite the fact that both the quality and composition of litter returned to the soil were significantly different across sites. We observed greater N resorption from senescing Acacia leaves at heavily browsed sites, which in turn contributed to increase the C:N ratio of leaf litter and caused greater litter N immobilization over time. This, together with the significantly lower tree- and herb-leaf litter mass beneath heavily browsed trees, should negatively affect decomposition rates. However, estimated dung and urine N deposition from both browsers and grazers was significantly greater at high- than at low-herbivory sites. We hypothesize that N inputs from dung and urine boost litter N mineralization and decomposition (especially following seasonal rainfall events), and thereby offset the effects of poor leaf litter quality at chronically browsed sites. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preference and Prey Switching in a Generalist Predator Attacking Local and Invasive Alien Pests

Invasive pest species may strongly affect biotic interactions in agro-ecosystems. The ability of generalist predators to prey on new invasive pests may result in drastic changes in the population dynamics of local pest species owing to predator-mediated indirect interactions among prey. On a short time scale, the nature and strength of such indirect interactions depend largely on preferences between prey and on predator behavior patterns. Under laboratory conditions we evaluated the prey preference of the generalist predator Macrolophus pygmaeus Rambur (Heteroptera: Miridae) when it encounters simultaneously the local tomato pest Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and the invasive alien pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). We tested various ratios of local vs. alien prey numbers, measuring switching by the predator from one prey to the other, and assessing what conditions (e.g. prey species abundance and prey development stage) may favor such prey switching. The total predation activity of M. pygmaeus was affected by the presence of T. absoluta in the prey complex with an opposite effect when comparing adult and juvenile predators. The predator showed similar preference toward T. absoluta eggs and B. tabaci nymphs, but T. absoluta larvae were clearly less attacked. However, prey preference strongly depended on prey relative abundance with a disproportionately high predation on the most abundant prey and disproportionately low predation on the rarest prey. Together with the findings of a recent companion study (Bompard et al. 2013, Population Ecology), the insight obtained on M. pygmaeus prey switching may be useful for Integrated Pest Management in tomato crops, notably for optimal simultaneous management of B. tabaci and T. absoluta, which very frequently co-occur on tomato.     

Seasonal and Spatial Variation in Hydrochemical Characteristics of a Semi-Arid River Basin,China

The analysis of river pollution and assessment of spatial and temporal variation in hydrochemistry is essential for control of river water pollution in China. Here, we investigated water quality issues based on an analysis of monitoring data from 32 sites in the Luanhe River Basin in northern China. During 2000–2010, flow and 12 hydrochemical parameters were monitored monthly in the main channel and breach streams. Hydrochemical characteristics of river water were assessed using the water quality identification index. Our results showed that concentrations were not necessarily related to flow. Flow was greatest in summer, but concentrations of nutrients and some heavy metal indicators were smallest in autumn; flow was smallest and concentrations of nutrients were greatest in winter, and concentrations of metals were greatest in spring. Hydrochemical parameters showed significant spatial variation as well; the most seriously polluted sites are located in urban areas, mainly due to discharge of wastewater from domestic and industrial sources. Sites with large and intermediate levels of pollution were located primarily in the main river channel and the larger tributaries, whereas sites of low-level pollution were in the smaller tributaries. Our findings provide valuable information for water pollution control in the Luanhe River Basin.     

Seasonal Foraging Ecology of Non-Migratory Cougars in a System with Migrating Prey

We tested for seasonal differences in cougar (Puma concolor) foraging behaviors in the Southern Yellowstone Ecosystem, a multi-prey system in which ungulate prey migrate, and cougars do not. We recorded 411 winter prey and 239 summer prey killed by 28 female and 10 male cougars, and an additional 37 prey items by unmarked cougars. Deer composed 42.4% of summer cougar diets but only 7.2% of winter diets. Males and females, however, selected different proportions of different prey; male cougars selected more elk (Cervus elaphus) and moose (Alces alces) than females, while females killed greater proportions of bighorn sheep (Ovis canadensis), pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus) and small prey than males. Kill rates did not vary by season or between males and females. In winter, cougars were more likely to kill prey on the landscape as: 1) elevation decreased, 2) distance to edge habitat decreased, 3) distance to large bodies of water decreased, and 4) steepness increased, whereas in summer, cougars were more likely to kill in areas as: 1) elevation decreased, 2) distance to edge habitat decreased, and 3) distance from large bodies of water increased. Our work highlighted that seasonal prey selection exhibited by stationary carnivores in systems with migratory prey is not only driven by changing prey vulnerability, but also by changing prey abundances. Elk and deer migrations may also be sustaining stationary cougar populations and creating apparent competition scenarios that result in higher predation rates on migratory bighorn sheep in winter and pronghorn in summer. Nevertheless, cougar predation on rare ungulates also appeared to be influenced by individual prey selection.     

Developmental Stage Age Groups and African Population Structure: The Kusasi of the West African Savanna

African population structures based on censuses exhibit a distinctive pattern of distortion. It is often assumed that the cause for this distortion is systematic biases in age estimates by census enumerators and respondents influenced by perceptions of social and biological development. African developmental stage age groups are the cultural codification of such perceptions. I describe developmental stage age groups among the Kusasi of Bawku District in northeast Ghana, and analyze their age and sex structure for a sample of 1,132 individuals from the village of Zorse. I show that differences between men and women reflect differences in biological and social development, and that cultural concepts of developmental stages could influence age estimates to produce the pattern of distortions typical of those found in African population structures based on censuses. This is supported by a comparison of Bawku District population structure based on the Ghana census and an ethnographic sample census in Zorse which eliminated most age estimate biases.     

A Meta-Analysis of the Impact of African Elephants on Savanna Vegetation

Abstract: Large herbivores such as elephants (Loxodonta africana) apparently have a negative impact on woody vegetation at moderate to high population densities. The confounding effects that fire, drought, and management history have may complicate assignment of such impacts to herbivory. We reviewed 238 studies published over 45 years and conducted a meta-analysis based on 21 studies that provided sufficient information on response of woody vegetation to elephants. We considered size and duration of studies, elephant densities, rainfall, fences, and study outcomes in our analysis. We detected a disproportionate citation of 20 published studies in our database, 15 of which concluded that woody vegetation responded negatively to elephants. Our analysis showed that high elephant densities had a negative effect on woody vegetation but that rainfall and presence of fences influenced these effects. In arid savannas, woody vegetation always responded negatively to elephants. In transitional savannas, an increase in elephant densities did not influence woody vegetation response. In mesic savannas, negative responses of woody vegetation increased when elephants occurred at higher densities, whereas elephants confined by fences also had more negative effects on woody plants than elephants that were not confined. Our analysis suggested that rainfall and fences influenced elephant density related impact and that research results were often site-specific. Local environmental conditions and site-specific objectives should be considered when developing management actions to curb elephant impacts on woody vegetation.     

Densities and biomasses of non-fossorial southern African Savanna rodents during the dry season

Summary Dry season densities of small non-fossorial rodents in five different savanna habitats ranged from 11 to 41 animals ha^-1 with corresponding live weights ranging from 310 g to 1557 g ha^-1. Average biomasses of small frodents in two representative savanna types, Burkea and Acacia savanna, were 912 g ha^-1 and 816 g ha^-1 respectively. These biomasses were similar to or even exceeded biomasses of other important consumers (birds, cattle, impala, and grasshoppers) in the savanna. Due to allometric relationships 1 kg of small savanna rodents is equivalent in energy consumption to 8 kg of impala (Aepyceros melampus) or 12.7 kg of cattle. The potential effect of small rodents on the savanna is therefore much larger than previously thought and needs further investigation.     

Ecological Engineering by a Mega-Grazer: White Rhino Impacts on a South African Savanna

Herbivory can change the structure and spatial heterogeneity of vegetation. We ask whether all species of grazers in a savanna ecosystem can have this effect or whether megaherbivores (>1000 kg) have a ‘special’ role that cannot be replicated by other species of grazers. We performed a replicated landscape scale experiment that examined the effects of White Rhino on the grass sward, on other species of grazing mammals and on the movement of fire through the landscape. White Rhino maintained short grass (‘lawn’) patches in mesic areas (∼750 mm pa) with increases in grass sward height when they were removed. Other species of grazers were unable to maintain short grass communities when White Rhino were removed. In semi-arid areas (∼600 mm pa) other, smaller grazers were able to maintain short grass communities in the absence of White Rhino and sward height did not increase. White Rhino removals affected fire by increasing fuel loads and fuel continuity. This resulted in larger, less patchy fires. We propose that the White Rhino acts as an influential ecosystem engineer, creating and maintaining short grass swards, which alter habitat for other grazers and change the fire regime. These results indicate the existence of context-dependent facilitation between White Rhino and other grazers in mesic, but not in semi-arid, savannas. Such top down effects on the ecosystem may have been much more widespread before the extinction of large grazers in the Pleistocene.     

Spatial Distribution of Aboveground Carbon Stock of the Arboreal Vegetation in Brazilian Biomes of Savanna,Atlantic Forest and Semi-Arid Woodland

The objective of this study was to map the spatial distribution of aboveground carbon stock (using Regression-kriging) of arboreal plants in the Atlantic Forest, Semi-arid woodland, and Savanna Biomes in Minas Gerais State, southeastern Brazil. The database used in this study was obtained from 163 forest fragments, totaling 4,146 plots of 1,000 m² distributed in these Biomes. A geographical model for carbon stock estimation was parameterized as a function of Biome, latitude and altitude. This model was applied over the samples and the residuals generated were mapped based on geostatistical procedures, selecting the exponential semivariogram theoretical model for conducting ordinary Kriging. The aboveground carbon stock was found to have a greater concentration in the north of the State, where the largest contingent of native vegetation is located, mainly the Savanna Biome, with Wooded Savanna and Shrub Savanna phytophysiognomes. The largest weighted averages of carbon stock per hectare were found in the south-center region (48.6 Mg/ha) and in the southern part of the eastern region (48.4 Mg/ha) of Minas Gerais State, due to the greatest predominance of Atlantic Forest Biome forest fragments. The smallest weighted averages per hectare were found in the central (21.2 Mg/ha), northern (20.4 Mg/ha), and northwestern (20.7 Mg/ha) regions of Minas Gerais State, where Savanna Biome fragments are predominant, in the phytophysiognomes Wooded Savanna and Shrub Savanna.     

Diet and Mandibular Morphology in African Apes

Investigations seeking to understand the relationship between mandibular form, function, and dietary behavior have focused on the mandibular corpus and symphysis. African apes vary along a gradient of folivory/frugivory, yet few studies have evaluated the morphology of the mandibular corpus and symphysis in these taxa, and the investigations have yielded mixed results. Specifically, studies using external metrics have identified differences in mandibular proportions that analysis of cortical bone distribution has not substantiated. I contribute to the ongoing debate on the relationship between jaw form and dietary behavior by comparing mandibular corporal and symphyseal shapes in African apes. Importantly, and in contrast to previous studies of African ape internal geometry, I include the Virunga mountain gorillas (Gorilla beringei beringei), the ape most specialized toward a folivorous diet. I test the hypotheses that 1) Gorilla beringei beringei always has significantly more robust mandibular corpora and symphyses, relative to mandibular length, than all other African apes and 2) all gorillas have significantly more robust mandibular corpora and symphyses, relative to mandibular length, than Pan. Results demonstrate that the folivorous mountain gorillas consistently exhibit a relatively wider mandibular symphysis and corpus than all other African apes. Furthermore, all gorillas consistently exhibit relatively more robust mandibular corporal and symphyseal dimensions than Pan. The results indicate that among African apes, mountain gorillas are better able to counter lateral transverse bending (wishboning) loads at the symphysis and torsional loads at the corpus. All gorillas are likewise better able to resist wishboning and vertical bending at the symphysis, and sagittal bending and torsion at the corpus, than Pan, findings that are consistent with masticating relatively tougher foods, repetitive loading of the jaws, or both. I offer possible explanations for the lack of concordance in results between studies that have analyzed the biomechanical properties of African ape mandibles and others that have relied on external metrics. More comprehensive study of the internal geometry of the mandible is needed to resolve whether African apes differ morphologically in ways predicted by dietary variation.

Herbaceous Forage and Selection Patterns by Ungulates across Varying Herbivore Assemblages in a South African Savanna

Herbivores generally have strong structural and compositional effects on vegetation, which in turn determines the plant forage species available. We investigated how selected large mammalian herbivore assemblages use and alter herbaceous vegetation structure and composition in a southern African savanna in and adjacent to the Kruger National Park, South Africa. We compared mixed and mono-specific herbivore assemblages of varying density and investigated similarities in vegetation patterns under wildlife and livestock herbivory. Grass species composition differed significantly, standing biomass and grass height were almost twice as high at sites of low density compared to high density mixed wildlife species. Selection of various grass species by herbivores was positively correlated with greenness, nutrient content and palatability. Nutrient-rich Urochloa mosambicensis Hack. and Panicum maximum Jacq. grasses were preferred forage species, which significantly differed in abundance across sites of varying grazing pressure. Green grasses growing beneath trees were grazed more frequently than dry grasses growing in the open. Our results indicate that grazing herbivores appear to base their grass species preferences on nutrient content cues and that a characteristic grass species abundance and herb layer structure can be matched with mammalian herbivory types.     

Predator-induced Swarms in the Tadpoles of an African Savanna Frog,Phrynomantis microps

Aggregations in tadpoles of the West African savanna frog Phrynomantis microps were often observed in their breeding ponds in our study area, situated in Comoé National Park, Ivory Coast. Experiments under seminatural conditions demonstrated that this behaviour was only shown while predators were present. The tadpoles reacted differently to different predators. Factors inducing swarm behaviour were optical (the predator) and/or chemical (liquid from injured tadpoles). Alarm substances are not species-specific. Kinship seems not to play a role in swarm formation.     

Seasonal variations in the density of a small West African lake

The seasonal variation in the vertical density profile of Lake Asejire waters was investigated from February 1974 to February 1976.The range of density was of the magnitude of 2.0 mg/cc, at the temperatures of Lake Asejire (21°C–32°C). Water densities were generally lower in the dry season when aquatic temperatures were high and generally higher in the rainy season when aquatic temperatures were low.During the dry season, the pycnocline was observed at 3m–7m in 1974 and 6 m–9 m in 1975. During periods of density stratification, the water body was clearly layered.Seasonal longitudinal differences in water density were such that during the floods of 1975 the inflow station waters had a higher density than the dam-site waters which however had a concomitantly higher conductivity. This suggests the insignificance of conductivity in water density changes in a lake with rather low conductivity values.     

Inventory and Bioindicator Sampling: Testing Pitfall and Winkler Methods with Ants in a South African Savanna

The sampling efficiency and consistency of pitfall traps and Winkler samples for inventory, bioindicator and ecological studies in savanna habitats was compared using ants. Pitfall traps are often used for ant collecting while Winkler litter sampling has until now had rather limited use. We test Winkler sampling for the first time in a South African savanna. Pitfall traps were more efficient and productive than Winkler sampling for epigaeic ants, with a greater total species richness and higher abundance of ants recorded. Winkler samples contributed few additional species. The relative abundance of different sized ants was different with the two collection methods. Winkler sampling was found to catch greater numbers of smaller ants than pitfall trapping, whereas pitfall trapping caught more larger ants. The standard collecting Winkler quadrat size of 1m² did not perform as well as 2× m² quadrats combined for one sample.     

Burning the Seasonal Mosaic: Preventative Burning Strategies in the Wooded Savanna of Southern Mali

Data are presented indicating a seasonal mosaic pattern of burning in the savanna of southern Mali. A seasonal mosaic is a landscape that is annually re-created by people, and which contains patches of unburned, early burned, and recently burned vegetation. A survey of over 100 farmers and in-depth interviews demonstrates that rural inhabitants of southern Mali begin an annual burning regime early in the dry season in order to fragment the landscape, with the goal of preventing later fires that can damage natural resources. The process of gradually burning off the driest vegetation creates a seasonal mosaic of habitat patches that increases the potential of the landscape for a variety of dry season land uses, including hunting, gathering of savanna products, and grazing. An analysis of a series of Landsat images shows that the practice of mosaic burning is widespread in the wooded savanna, in which burning usually begins early and large fires are rare. On the basis of recent developments in ecological theory and empirical evidence from similar burning regimes in parts of Australia, it is suggested that seasonal mosaic burning in Mali not only prevents damaging late-season fires but increases biodiversity. It is concluded that discourse on African savanna burning overemphasizes the ecologically detrimental aspects of fire, while neglecting the beneficial ones resulting in misguided policies that pose a threat to human livelihoods and savanna ecosystems.