The Long-Term Effects of Abundant Elephant Carcasses on the Population Dynamics of a Facultative Scavenger Predator and Its Prey

Core Concepts

The abundance of elephant carcasses, a major food source for facultative scavengers, does not profoundly affect the long-term population dynamics of a large carnivore predator (spotted hyaena) and its prey in an African savanna ecosystem.

Abstract

This study explores the long-term effects of elephant carcass availability on the population dynamics of a large mammalian carnivore, the spotted hyaena, and its prey in Hwange National Park, Zimbabwe. The park experienced fluctuations in elephant carcass abundance due to management practices, providing a semi-natural experiment to assess the impacts of scavenging on predation.
Key highlights:

The study used a 50-year dataset and Multivariate Autoregressive State Space models to estimate hyaena and prey densities over four periods with contrasting elephant carrion availability.
Models with period-dependent growth rates explained variations in hyaena and prey densities better than constant or time-varying models, indicating an effect of management measures on their population dynamics.
However, the overall patterns suggest that hyaena population dynamics primarily follow those of its prey, regardless of elephant carcass availability.
Some subtle patterns could be interpreted as consequences of changes in predation pressure following changes in scavenging opportunities, but signals of prey-predator decoupling were not strongly observed.
The authors discuss why inputs of mega-carcasses as pulsed resources may have limited long-term impacts on the classical predator-prey coupling in diverse African savanna ecosystems.

Stats

"Hyaena and prey densities showed similar trends across the 4 study periods: the two populations increased during period 1, stabilized during period 2, decreased during period 3, and increased again during period 4."
"Differences between growth rate of hyaena and prey are similar in both periods when elephant carcasses were less abundant (0.069 in the second and 0.063 in the fourth period). During periods 1 and 3 characterized by increased abundance of elephant carrion in the landscape, this difference was increased or decreased (0.123 during the first and 0.004 during the third period)."

Quotes

"Surprisingly, little is known about the cumulative long-term effects of these changes and the ultimate implication for population dynamics of predators able of facultative scavenging and their prey."
"Overall, these patterns are indicative of a numerical response of hyaena to the increased elephant carcass availability, through a rapid increase in density in period 1 and the maintenance of densities higher than at the start of our study period in period 3."

Key Insights Distilled From

Insights on the effect of mega-carcass abundance on the population dynamics of a facultative scavenger predator and its prey

by Sidous,M., C... at www.biorxiv.org 11-13-2023

https://www.biorxiv.org/content/10.1101/2023.11.08.566247v2

Deeper Inquiries

How might the frequency and intensity of carrion pulses, potentially altered by global changes and human activities, affect the coupling between large carnivores and their live prey populations in the long run?

The frequency and intensity of carrion pulses, influenced by global changes and human activities, can have significant effects on the coupling between large carnivores and their live prey populations in the long run. Changes in the availability of carrion, such as those resulting from extreme weather events or anthropogenic activities, can disrupt the natural dynamics of predator-prey interactions.
For large carnivores like hyaenas, which are facultative scavengers, alterations in the frequency and intensity of carrion pulses can lead to shifts in their foraging behavior and diet composition. If the availability of carrion increases due to factors like climate change-induced droughts or human-provided carcasses, hyaenas may rely more on scavenging and less on hunting live prey. This shift in feeding behavior can have cascading effects on the population dynamics of both hyaenas and their live prey.
In the long run, if the frequency and intensity of carrion pulses continue to change, large carnivores like hyaenas may become more dependent on scavenging as a food source. This increased reliance on carrion could potentially lead to changes in predator densities, distribution patterns, and hunting strategies, ultimately impacting the abundance and behavior of their live prey populations. Therefore, understanding and monitoring the effects of altered carrion pulses on predator-prey dynamics is crucial for the conservation and management of these ecosystems.

What other factors, such as the role of other large carnivores or climatic conditions, could have influenced the population trends of hyaena and its prey in this ecosystem?

In addition to the availability of carrion and its impact on hyaena and prey populations, several other factors could have influenced the population trends in this ecosystem. The role of other large carnivores, such as lions, in the area can significantly affect hyaena and prey dynamics. Competition for resources, predation pressure, and potential interactions between different predator species can all shape the population trends of hyaenas and their prey.
Climatic conditions, particularly rainfall patterns, play a crucial role in determining food availability and habitat quality for both hyaenas and their prey. Droughts or periods of low rainfall can lead to food scarcity, impacting the survival and reproduction of herbivores, which in turn affects hyaena populations. Conversely, abundant rainfall can result in increased vegetation growth, providing more food resources for herbivores and subsequently influencing predator-prey dynamics.
Furthermore, habitat changes, human disturbances, disease outbreaks, and anthropogenic activities like poaching can also influence the population trends of hyaenas and their prey. Understanding the complex interactions between these various factors is essential for comprehensively assessing the dynamics of predator-prey relationships in the ecosystem.

What insights could be gained by comparing the diet and hunting behavior of hyaena in drought years (high elephant mortality) versus years with good rainfall (low elephant mortality)?

Comparing the diet and hunting behavior of hyaenas in drought years with high elephant mortality versus years with good rainfall and low elephant mortality can provide valuable insights into the adaptive strategies of these predators in response to changing environmental conditions.
In drought years with high elephant mortality, hyaenas may rely more heavily on scavenging elephant carcasses as a food source. This could lead to shifts in their dietary preferences, energy expenditure, and social behavior. Studying their diet composition during these periods can reveal the extent of their dependence on carrion and the impact of this reliance on their overall foraging ecology.
Conversely, in years with good rainfall and low elephant mortality, hyaenas may exhibit different hunting behaviors and prey preferences. With ample food resources available from live prey species, hyaenas may adjust their hunting strategies, target different prey species, and exhibit variations in their social dynamics. Comparing these behaviors to drought years can highlight the flexibility and adaptability of hyaenas in response to changing environmental conditions.
Overall, such comparisons can shed light on the resilience of hyaenas to environmental fluctuations, the importance of carrion as a food source, and the dynamics of predator-prey interactions in the ecosystem. This information is crucial for understanding the ecological roles of hyaenas and their contributions to the overall biodiversity and stability of the ecosystem.