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. 2014 Oct 7;111(40):14472-7.
doi: 10.1073/pnas.1408471111. Epub 2014 Sep 8.

Collapse of an ecological network in Ancient Egypt

Justin D Yeakel  1 , Mathias M Pires  2 , Lars Rudolf  3 , Nathaniel J Dominy  4 , Paul L Koch  5 , Paulo R Guimarães Jr  2 , Thilo Gross  3
Affiliations

Collapse of an ecological network in Ancient Egypt

Justin D Yeakel et al. Proc Natl Acad Sci U S A. .

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.

Keywords: community stability; dynamic sensitivity; historical ecology; redundancy; trophic interactions.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Ancient Egyptian depictions of familiar predator–prey interactions. The (A) obverse and (B) reverse surfaces of a siltstone ceremonial palette accessioned (no. E.3924) in the Ashmolean Museum of Art and Archaeology, University of Oxford. The palette (known informally as the Ashmolean or two dog palette) was recovered from the main deposit at Hierakonpolis (∼5,150 y B.P.). The object is surmounted and framed by two wild dogs (Lycaon pictus) clasping one another’s paws. Other unambiguous species include ostrich, hartebeest, wildebeest, ibex, oryx, and giraffe. Some fictitious animals are also depicted, including serpent-necked panthers, or “serpopards”, and a plausible griffin; these animals were excluded from our analysis. Photographs reproduced with permission (Copyright, Ashmolean Museum). (C) Line drawing of a mudstone ceremonial palette accessioned (no. EA20790) in the British Museum. The provenance of this Late Predynastic palette (known informally as the hunters’ palette) is uncertain. The reliefs depict human hunters stalking and capturing lions, gazelles, hartebeest, and an ostrich with bows, spears, throwsticks, and lariat. For recent scholarship on, and interpretation of, these images, see Davis (57).
Fig. 2.
Fig. 2.
The presence/absence of large-bodied mammalian species across six millennia of Egyptian history. All dates are in years before present, thus “years before 1950 A.D.,” such that we distinguish 0 y B.P. (1950 A.D.) from “today” (established as 2010 A.D.). The first time bin does not have a definitive starting date, generally representing the Late Pleistocene. The white circles denote the first time interval of a recorded species occurrence if it was not initially present; the black circles denote the last time interval of a recorded species occurrence if it is not extant. The color gradient is the probability that a given species is locally extinct for the treatment allowing first/last occupation to vary across two time bins before and after the recorded event. G-R, Greco-Roman.
Fig. 3.
Fig. 3.
Changes in the predator–prey ratio and dynamic stability of the Egyptian trophic network over time. (A) The predator–prey ratio is shown (black line) against simulations where extinction is treated probabilistically, incorporating error of 286 (dark blue polygon) and 580 (lighter blue polygon) years before and after first and last occurrences (the mean is denoted by the blue line). Random extinction trajectories are shown by the red line and polygon (mean and SD of 5 × 105 replicates, respectively). (B) Proportion of stable webs (2 × 105 replicates) for the Egyptian community (black), and with first and last appearances treated probabilistically, incorporating error of 286 (dark blue, dashed line) and 580 (lighter blue dotted line) years before and after the first and last occurrences. The vertical dashed lines denote the major climatic events at ∼5,050, 4,170, and 3,035 y B.P.
Fig. 4.
Fig. 4.
(A) The mean change in PSW (ΔPSW) as a function of species presence over time. Predator presence destabilizes trophic network (stippled lines); prey presence stabilizes trophic networks (solid lines). Histograms on the y axes represent densities of ΔPSW values for the earliest and latest time intervals, and colors scale to the y axis. (B) PSW (colors scaled from red, PSW = 0, to blue, PSW = 1) as a function of the sensitivity of herbivore growth to changes in herbivore density (ϕ; y axis) over time (x axis). The white stippled line denotes ϕ = 0.5 used for the dynamic analysis (Table S1), such that ϕ > 0.5 indicates nutrient enrichment (productivity increase), and ϕ < 0.5 indicates nutrient rarefaction (productivity decrease). (C) Species sensitivity vs. persistence since the Pleistocene–Holocene transition (11.7 ky B.P.). Linear regression model: R2 = 0.36, p ≪ 0.005; blue shaded region is the 75% confidence interval.
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