Collapse of an ecological network in Ancient Egypt

Abstract

The dynamics of ecosystem collapse are fundamental to determining how and why biological communities change through time, as well as the potential effects of extinctions on ecosystems. Here, we integrate depictions of mammals from Egyptian antiquity with direct lines of paleontological and archeological evidence to infer local extinctions and community dynamics over a 6,000-y span. The unprecedented temporal resolution of this dataset enables examination of how the tandem effects of human population growth and climate change can disrupt mammalian communities. We show that the extinctions of mammals in Egypt were nonrandom and that destabilizing changes in community composition coincided with abrupt aridification events and the attendant collapses of some complex societies. We also show that the roles of species in a community can change over time and that persistence is predicted by measures of species sensitivity, a function of local dynamic stability. To our knowledge, our study is the first high-resolution analysis of the ecological impacts of environmental change on predator-prey networks over millennial timescales and sheds light on the historical events that have shaped modern animal communities.community stability | historical ecology | trophic interactions | dynamic sensitivity | redundancy M odern biological communities are vestiges, with rich ecological ancestries shaped by evolutionary, climatic, and more recently anthropogenic effects. Determining the consequences of past ecological disturbance will inform predictions of how modern communities may respond to ongoing anthropogenic or climatic pressures. Of particular importance are extinction cascades (1, 2), which can lead to trophic downgrading and community collapse by altering the structure (2) and relative strengths of interactions between species (3). Examining the long-term effects of extinctions on communities can only be accomplished by studying past ecosystems (4). The paleontological record and the remarkable historical record of species occurrences in Egypt document a biological community changing in the face of increasing aridification and human population densities (5). The timing and pattern of animal extinctions in Egypt are thus well suited to illuminate our understanding of how the structure and functioning of biotic communities are altered by changing climatic and anthropogenic impacts.The Nile Valley north of Aswan is known for its intense heat, low rainfall, and relatively sparse vegetation. In fact, the last 2,750 km of the Nile is devoid of water-bearing tributaries and surrounded by desert with an average rainfall of 3.4 cm/y. The Egyptian landscape in the Late Pleistocene/early Holocene was very different; during the African Humid Period (AHP) (14,800-5,500 y B.P.), the region had a cooler, wetter climate driven by heavy monsoonal rains (5). These factors contributed to a diverse assemblage of mammals that bears a strong resemblance to communities in East Africa today.Termination of the AHP was associated with increasingly wea...

Biology in the Anthropocene: Challenges and insights from young fossil records

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“…In a recent study, Yeakel et al (88) reconstructed 6,000 y of species' occurrence and their trophic networks in ancient Egypt, demonstrating how aridification pulses, hunting, and habitat competition by growing populations affected species composition, and how species extinctions were dynamically destabilizing for the Egyptian ecosystem. Both anthropogenic and climatic disturbances led to the extinction of larger-bodied species; stability decreased markedly around 3000 BC, and further declined around 2000 BC (in both instances following aridification pulses) before falling precipitously in the last 150 y, resulting in a contemporary community highly sensitive to additional perturbations.…”

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Mammalian extinction in ancient Egypt, similarities with the southern Levant

“…Yeakel et al (1) find that wild mammal extinction in ancient Egypt during the Holocene was nonrandom and coincided with abrupt climatic changes and a local cultural collapse. The authors provide compelling evidence that the deterioration of the natural Egyptian ecosystem gradually progressed during the Holocene.…”

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