1. Ecology

Relative demographic susceptibility does not explain the extinction chronology of Sahul's megafauna

  1. Corey J A Bradshaw  Is a corresponding author
  2. Christopher N Johnson
  3. John Llewelyn
  4. Vera Weisbecker
  5. Giovanni Strona
  6. Frédérik Saltré
  1. Flinders University, Australia
  2. University of Tasmania, Australia
  3. University of Helsinki, Finland
https://doi.org/10.7554/eLife.63870
Share this article
Cite this article
  1. Corey J A Bradshaw
  2. Christopher N Johnson
  3. John Llewelyn
  4. Vera Weisbecker
  5. Giovanni Strona
  6. Frédérik Saltré
(2021)
Relative demographic susceptibility does not explain the extinction chronology of Sahul's megafauna
eLife 10:e63870.
https://doi.org/10.7554/eLife.63870
  2. Download BibTeX
  3. Download .RIS

Abstract

The causes of Sahul's megafauna extinctions remain uncertain, although several interacting factors were likely responsible. To examine the relative support for hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as eight extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Our models show that the macropodiformes were the least demographically susceptible to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation scenario, while body mass and generation length explained much of the variation in relative risk. Our results reveal that the actual mechanisms leading to the observed extinction chronology were unlikely related to variation in demographic susceptibility per se, but were possibly driven instead by finer-scale variation in climate change and/or human prey choice and relative hunting success.

Data availability

All data and are R code needed to reproduce the analyses are available for download at github.com/cjabradshaw/MegafaunaSusceptibility.

The following previously published data sets were used
    1. Peters
    2. K. J.
    3. Saltré
    4. F.
    5. Friedrich
    6. T.
    7. Jacobs
    8. Z.
    9. Wood
    10. R.
    11. McDowell
    12. M.
    13. Ulm
    14. S.
    15. Bradshaw
    16. C.J.A
    (2019) FosSahul 2.0
    doi:10.1038/s41597-019-0267-3Fisher, D. O., Owens, I. P. F., and Johnson, C. N. (2001). The ecological basis of life history variation in marsupials. Ecology 82, 3531-3540. doi: 10.1890/0012-9658(2001)082[3531:TEBOLH]2.0.CO;2.
    http://doi.org/10.1038/s41597-019-0267-3

Article and author information

Author details

  1. Corey J A Bradshaw

    Global Ecology, College of Science and Engineering, Flinders University, Adelaide, Australia
    For correspondence
    corey.bradshaw@flinders.edu.au
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-5328-7741

  2. Christopher N Johnson

    Dynamics of Eco-Evolutionary Pattern, University of Tasmania, Hobart, Australia
    Competing interests
    The authors declare that no competing interests exist.

  3. John Llewelyn

    Global Ecology, College of Science and Engineering, Flinders University, Adelaide, Australia
    Competing interests
    The authors declare that no competing interests exist.

  4. Vera Weisbecker

    Global Ecology, College of Science and Engineering, Flinders University, Adelaide, Australia
    Competing interests
    The authors declare that no competing interests exist.

  5. Giovanni Strona

    Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-2294-4013

  6. Frédérik Saltré

    Global Ecology, College of Science and Engineering, Flinders University, Adelaide, Australia
    Competing interests
    The authors declare that no competing interests exist.

Funding

Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage (CE170100015)

  • Corey J A Bradshaw
  • Christopher N Johnson
  • Vera Weisbecker

Australian Research Council (DP170103227)

  • Vera Weisbecker

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

© 2021, Bradshaw et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 2,210
    views
  • 278
    downloads
  • 14
    citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Corey J A Bradshaw
  2. Christopher N Johnson
  3. John Llewelyn
  4. Vera Weisbecker
  5. Giovanni Strona
  6. Frédérik Saltré
(2021)
Relative demographic susceptibility does not explain the extinction chronology of Sahul's megafauna
eLife 10:e63870.
https://doi.org/10.7554/eLife.63870

Share this article

https://doi.org/10.7554/eLife.63870

Categories and tags

Further reading

    1. Ecology

    Combining radio-telemetry and radar measurements to test optimal foraging in an aerial insectivore bird

    Itai Bloch, David Troupin ... Nir Sapir
    Research Article

    Optimal foraging theory posits that foragers adjust their movements based on prey abundance to optimize food intake. While extensively studied in terrestrial and marine environments, aerial foraging has remained relatively unexplored due to technological limitations. This study, uniquely combining BirdScan-MR1 radar and the Advanced Tracking and Localization of Animals in Real-Life Systems biotelemetry system, investigates the foraging dynamics of Little Swifts (Apus affinis) in response to insect movements over Israel’s Hula Valley. Insect movement traffic rate (MoTR) substantially varied across days, strongly influencing swift movement. On days with high MoTR, swifts exhibited reduced flight distance, increased colony visit rate, and earlier arrivals at the breeding colony, reflecting a dynamic response to prey availability. However, no significant effects were observed in total foraging duration, flight speed, or daily route length. Notably, as insect abundance increased, inter-individual distances decreased. These findings suggest that Little Swifts optimize their foraging behavior in relation to aerial insect abundance, likely influencing reproductive success and population dynamics. The integration of radar technology and biotelemetry systems provides a unique perspective on the interactions between aerial insectivores and their prey, contributing to a comprehensive understanding of optimal foraging strategies in diverse environments.

    1. Ecology
    2. Evolutionary Biology

    Passive accumulation of alkaloids in inconspicuously colored frogs refines the evolutionary paradigm of acquired chemical defenses

    Rebecca D Tarvin, Jeffrey L Coleman ... Richard W Fitch
    Research Article

    Understanding the origins of novel, complex phenotypes is a major goal in evolutionary biology. Poison frogs of the family Dendrobatidae have evolved the novel ability to acquire alkaloids from their diet for chemical defense at least three times. However, taxon sampling for alkaloids has been biased towards colorful species, without similar attention paid to inconspicuous ones that are often assumed to be undefended. As a result, our understanding of how chemical defense evolved in this group is incomplete. Here, we provide new data showing that, in contrast to previous studies, species from each undefended poison frog clade have measurable yet low amounts of alkaloids. We confirm that undefended dendrobatids regularly consume mites and ants, which are known sources of alkaloids. Thus, our data suggest that diet is insufficient to explain the defended phenotype. Our data support the existence of a phenotypic intermediate between toxin consumption and sequestration — passive accumulation — that differs from sequestration in that it involves no derived forms of transport and storage mechanisms yet results in low levels of toxin accumulation. We discuss the concept of passive accumulation and its potential role in the origin of chemical defenses in poison frogs and other toxin-sequestering organisms. In light of ideas from pharmacokinetics, we incorporate new and old data from poison frogs into an evolutionary model that could help explain the origins of acquired chemical defenses in animals and provide insight into the molecular processes that govern the fate of ingested toxins.

    1. Ecology

    Disease Transmission: Interactions between wild pigs and the spread of disease

    Mercury Shitindo
    Insight

    Tracking wild pigs with GPS devices reveals how their social interactions could influence the spread of disease, offering new strategies for protecting agriculture, wildlife, and human health.