Data from: Density dependence in demography and dispersal generates fluctuating invasion speeds

Density dependence plays an important role in population regulation and is
known to generate temporal fluctuations in population density. However,
the ways in which density dependence affects spatial population processes,
such as species invasions, are less understood. Although classical
ecological theory suggests that invasions should advance at a constant
speed, empirical work is illuminating the highly variable nature of
biological invasions, which often exhibit nonconstant spreading speeds,
even in simple, controlled settings. Here, we explore endogenous density
dependence as a mechanism for inducing variability in biological invasions
with a set of population models that incorporate density dependence in
demographic and dispersal parameters. We show that density dependence in
demography at low population densities—i.e., an Allee effect—combined with
spatiotemporal variability in population density behind the invasion front
can produce fluctuations in spreading speed. The density fluctuations
behind the front can arise from either overcompensatory population growth
or density-dependent dispersal, both of which are common in nature. Our
results show that simple rules can generate complex spread dynamics and
highlight a source of variability in biological invasions that may aid in
ecological forecasting.