Written by Mazz Cummings

During the 21^st century, we are currently undergoing the sixth known mass extinction. Extinctions are a normal part of evolution, and occur for a variety of different reasons including changing environmental conditions, and competition dynamics both within and between species. Some sources suggest that current rates of extinction are around 100 times higher than the usual ‘background’ rate of extinction, while other sources suggest this rate is closer to 1,000 or even 10,000 times higher. Understanding extinction dynamics can help us to slow the current rate of biodiversity loss, and begin to mitigate the impacts that lead to ecosystem tipping points.

Simulating a case study

In their investigation, Ms Miriam Kopels and Dr Isaac Ullah developed a model to simulate the interactions within a socio-ecological system, using the case study of the extinction of Syncerus antiquus , the African giant Buffalo, 10 – 12 thousand years ago. The system under investigation was based in the Cape Floristic region of South Africa, a grassland ecosystem, during the Pleistocene – Holocene transition (around 10 - 12 thousand years ago). During this period, the climate was transitioning out of the last glacial maximum, with colder, wetter conditions and a year round growing season, to a hotter, drier climate, and more distinct rainfall patterns and growing seasons.

Socio-ecological system: A complex and dynamic bio-geo-physical unit in which humans and nature are inextricably linked. Changes to one component of the system can have drastic consequences to another component of the system.

Syncerus antiquus: An extinct species of buffalo, standing at approximately 2 metres tall, with horns spanning around 3 meters. Remains of this buffalo species have been found in Southern, Eastern and Northern Africa, including evidence of human hunting of this species in the region and timeframe of the case study

Miriam was inspired to carry out this investigation after reading a 1970s report by Richard Klein. She says “Without the benefit of sophisticated computing algorithms, Klein looked at the fossil record of S. antinquus and posited that the unique survival curve was likely the result of human behaviour. Specifically, that we were overhunting females and their young. He hypothesized that this might have been a key factor contributing to the extinction of the animal.”

This case study has previously inspired hypotheses focusing on single causal factors of the extinction of S. antiquus. Dr Ullah tells us that “There was enough tantalizing empirical evidence to suggest that humans could have played a role… but there was equal evidence that rapid environmental changes happening at the end of the last Ice Age were also potentially to blame.” This was the perfect opportunity to generate a model to investigate the intricate relationships and cross-feedbacks between different components of the socio-ecological system.

Making a system based Model

Developing a model isn’t easy, as Miriam swiftly discovered. “I remember the day I naively approached Dr. Isaac Ullah with the data from Klein, thinking it would be “easy” to change some code around and put together an agent-based model to test Klein’s hypothesis. I thought it would take months. No, it took years.” Developing models such as these involves writing complex code and developing several experimental parameters. In total, they developed 24 distinct modelling experiments, each of which was conducted 40 times for a total of 960 simulations. “These experiments are huge” Miriam says. “They take days to run, so each misstep would potentially cost us weeks, even longer if we had to re-write a results section. The original draft of the manuscript was over 40 pages!”

A complex system

The interesting strategy of overhunting females and their young Miriam had initially detected in Klein’s data was highlighted in the results of the model, primarily as a symptom of male buffalo aggression. This factor had the largest influence on the speed of extinctions. If male buffalo are more aggressive and dangerous to hunt, they are effectively not worth the risk when there are other, more vulnerable targets and “hungry people out looking for their next meal.” Would you risk it for a chocolate biscuit? Yeah probably. Would you risk it for a big angry buffalo? Probably not. But targeting females and their young has devastating consequences for the breeding capacity in animals such as S. antiquus, particularly when they take several years to reach sexual maturity, and are only able to have one calf every two to three years.

Miriam and Isaac also uncovered interactions between human presence and changing environmental conditions, with changes to one component of the socio-ecological system often impacting another component, influencing the overall outcome of the model simulation. The highly sensitive and complex dynamics within the model showed that extinction was not always inevitable, even in scenarios where human hunting pressure was high, and environmental conditions were poor, the two key factors at the heart of prior hypotheses. The model helped to develop an understanding of the various cross-feedbacks within the system, and how changes to one component influence the whole systems dynamics, and the overall outcome of the simulation.

What next?

The results from Miriam and Dr Ullah’s investigation highlight the inextricable relationship between humans and nature in socio-ecological systems, and the complex dynamics that influence a species success or failure under a given set of circumstances. Miriam says that, not only is the model useful to inspire new questions and generate new ideas, but “I think the model is particularly well suited for co-evolutionary hypotheses because we include the animal life history[in the model], including things like interbirth interval and time spent weaning calves.” The ability to adapt the model to different species means it has the potential to reveal insights into a myriad of different socio-ecological systems, and help to inform conservation management.

In his current research, Dr Ullah has adapted the model to investigate cattle herds in the vicinity of Spanish “missions” in Southern Arizona in the early post-contact period. “Here, we are looking at understanding the carrying capacity of these landscapes, and what the environmental impacts of the introduction of cattle and horses may have been. We also aim to understand the autonomy of native peoples in relation to the introduction of these animals into the ecosystem, and how new types of relationships emerged between various groups of people in this area at that time that subvert the normal narrative of colonialism.”

Understanding and developing models such as these can highlight the intricacies of dynamic relationships within a system, and highlight factors, as demonstrated by Ms Miriam Kopels and Dr, Isaac Ullah in their model, that influence a species towards or away from extinction thresholds, which can help to inform modern and future conservation efforts. We wish Miriam luck in her PhD and look forward to seeing how this model is used in future investigations!

Bio

Original paper: https://doi.org/10.1017/qua.2024.6

Ms Miriam Kopels

Miriam is a biocultural anthropologist largely interested in human subsistence, diet, and nutrition, currently studying for a PhD at the University of Nevada, Las Vegas. Miriam started on this project with Dr. Ullah in 2019, and the long wait for publication was truly worth it. Miriam uses the model in presentations at elementary schools, showing children how to generate hypotheses and understand fossil records.

Dr Isaac Ullah

Dr Isaac Ullah is an archaeologist and associate Professor of Anthropology, San Diego State University specialising in the use of computer models to understand the dynamics of past societies. Dr Ullah is particularly interested in human impacts on the environment and how human behaviour has shaped the world over the past many millennia since our species evolved.

Website: https://isaacullah.github.io/