title: Seed viability and germination success of Acacia tortilis along land-use and aridity gradients in the Eastern Sahara.
abstract: Our study focuses on the keystone species Acacia tortilis and is the first to investigate the effect of domestic ungulates and aridity on seed viability and germination over an extensive part of the Eastern Sahara. Bruchids infest its seeds and reduce their viability and germination, but ingestion by ruminant herbivores diminishes infestation levels and enhances/promotes seed viability and germination. The degree of these effects seems to be correlated with animal body mass. Significantly reduced numbers of wild ruminant ungulates have increased the potential importance of domestic animals and pastoral nomadism for the functionality of arid North African and Middle Eastern ecosystems. We sampled seeds (16,543) from A. tortilis in eight areas in three regions with different aridity and land use. We tested the effect of geography and sampling context on seed infestation using random effects logistic regressions. We did a randomized and balanced germination experiment including 1193 seeds, treated with different manure. Germination time and rates across geography, sampling context, and infestation status were analyzed using time-to-event analyses, Kaplan-Meier curves and proportional hazards Cox regressions. Bruchid infestation is very high (80%), and the effects of context are significant. Neither partial infestation nor adding manure had a positive effect on germination. There is a strong indication that intact, uningested seeds from acacia populations in the extremely arid Western Desert germinate more slowly and have a higher fraction of hard seeds than in the Eastern Desert and the Red Sea Hills. For ingested seeds in the pastoralist areas we find that intact seeds from goat dung germinate significantly better than those from camel dung. This is contrary to the expected body-mass effect. There is no effect of site or variation in tribal management.
authors.affiliation: UNI Research Environment P O Box 7810 5020 Bergen Norway; Department of Geography University of Bergen P O Box 7802 5020 Bergen Norway.
authors.forename: Gidske Leknæs
authors.initials: GL
authors.lastname: Andersen
authors.affiliation: UNI Research Environment P O Box 7810 5020 Bergen Norway; Department of Biology University of Bergen P O Box 7800 5020 Bergen Norway.
authors.forename: Knut
authors.initials: K
authors.lastname: Krzywinski
authors.affiliation: Norwegian Institute of Public Health P O Box 4404 Nydalen 0403 Oslo Norway; Department of Global Public Health and Primary Care University of Bergen Bergen Norway.
authors.forename: Håkon K
authors.initials: HK
authors.lastname: Gjessing
authors.affiliation: Department of Linguistic, Literary and Aesthetic Studies University of Bergen Sydnesplassen 7 5007 Bergen Norway.
authors.forename: Richard Holton
authors.initials: RH
authors.lastname: Pierce
keywords: Body‐mass; bruchid infestation; camel; dung; nomadic pastoralism; ovicaprids; ruminant herbivores; seed dormancy
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