Soil nutrient status determines how elephant utilize trees and shape environments

Abstract

Summary1. Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk, the African elephant. 2. We introduce the concept of nutrient load as the product of patch size, number of patches and local patch nutrient concentration. Nutrient load provides a novel spatially explicit expression of the total available nutrients a herbivore can select from. 3. We hypothesized that elephant would select nutrient-rich patches, based on the nutrient load per 2500 m 2 down to the individual plant scale, and that this selection will depend on the nitrogen and phosphorous contents of plants. 4. We predicted that elephant would cause more adverse impact to trees of lower value to them in order to reach plant parts with higher nutrient concentrations such as bark and root. However, elephant should maintain nutrient-rich trees by inducing coppicing of trees through re-utilization of leaves. 5. Elephant patch selection was measured in a homogenous tree species stand by manipulating the spatial distribution of soil nutrients in a large field experiment using NPK fertilizer. 6. Elephant were able to select nutrient-rich patches and utilized Colophospermum mopane trees inside these patches more than outside, at scales ranging from 2500 down to 100 m 2 . 7. Although both nitrogen and phosphorus contents of leaves from C. mopane trees were higher in fertilized and selected patches, patch choice correlated most strongly with nitrogen content. As predicted, stripping of leaves occurred more in nutrient-rich patches, while adverse impact such as uprooting of trees occurred more in nutrient-poor areas. 8. Our results emphasize the necessity of including scale-dependent selectivity in foraging studies and how elephant foraging behaviour can be used as indicators of change in the availability of nutrients.

Usual Populations, Unusual Individuals: Insights into the Behavior and Management of Asian Elephants in Fragmented Landscapes

“…The availability and distribution of resources seem to primarily influence the occurrence of elephants in a particular region [3]–[7]. Although this species does not have any natural predator [3], humans and anthropogenic disturbances have, over time, emerged as major threats to these mammals, occasionally threatening their very survival.…”

Temporal variation in resource selection of African elephants follows long‐term variability in resource availability

“…, Pretorius et al. ). Although elephants feed on a great variety of species, they exhibit selectivity in regards to plant parts and nutrient content.…”

“…Moreover, large areas in Etosha are dominated by Colophospermum mopane trees, which might not supply the adequate nitrogen and phosphorus content needed for elephants (Pretorius et al. , Turner et al. ).…”

Elephant both Increase and Decrease Availability of Browse Resources for Black Rhinoceros

“…In succulent thicket, this results in the near complete replacement of the thicket shrub community with grasses (Landman et al 2012), and therefore the near loss of browsing opportunities. As our experimental transects were generally placed on even terrain with similar soils (a proxy for food quality; Kohi et al 2011, Pretorius et al 2011), we expected surface water availability to be the primary determinant of elephant effects at this scale. Hapoor is located in the area of AMC originally fenced in 1954 (Site 1), and is one of only two water points that have maintained water availability for elephant since the initial fencing.…”