Abstract
Emigration is a fundamental process affecting species local, regional, and large-scale dynamics. The
paradigmatic view in ecology is that emigration is density independent (DIE) or positive density-
dependent (+DDE). However, alternative forms are biologically plausible, including negative (−DDE), u-
shaped (uDDE), and hump-shaped (hDDE) forms. We reviewed the empirical literature to assess the
frequency of different forms of density-dependent emigration and whether the form depended on
methodology. We also developed a reaction-diffusion model to illustrate how different forms of DDE
can affect patch-level population persistence. We found 145 studies, the majority representing DIE
(30%) and +DDE (36%). However, we also regularly found −DDE (25%) and evidence for nonlinear DDE
(9%), including one case of uDDE and two cases of hDDE. Nonlinear DDE detection is likely hindered by
the use of few density levels and small density ranges. Based on our models, DIE and +DDE promoted
stable and persistent populations. uDDE and −DDE generated an Allee effect that decreases minimum
patch size. Lastly, −DDE and hDDE models yielded bistability that allows the establishment of
populations at lower densities. We conclude that the emigration process can be a diverse function of
density in nature and that alternative DDE forms can have important consequences for population
dynamics.
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