Density dependence slows invader spread in fragmented landscapes

Area of Science:

• Ecology
• Invasive Species Biology
• Spatial Dynamics

Background:

• Invasive species spread models often assume homogeneous environments.
• Density dependence's role in spread through heterogeneous landscapes is poorly understood.
• Existing models typically link spread velocity to rare-stage growth and dispersal, not competition.

Purpose of the Study:

• To investigate how landscape patchiness affects density dependence in invasive plant spread.
• To determine if intraspecific competition influences invasion velocity in heterogeneous habitats.
• To develop models that incorporate landscape structure and population dynamics.

Main Methods:

• Utilized simulation models and analytical approximations.
• Explored annual plant invaders in landscapes with habitat gaps.
• Adapted stochastic dispersal and Markov chain models for different gap sizes.

Main Results:

• Landscape patchiness and discrete population size create a strong density-dependent effect.
• Intraspecific competition significantly decelerated invasion spread through patchy landscapes.
• Continuous density models did not show the same density-dependent slowdown.

Conclusions:

• Density dependence, particularly intraspecific competition, is crucial for predicting invader spread in patchy habitats.
• Ecological models must consider reproduction at both low and high densities.
• Habitat heterogeneity fundamentally alters the dynamics of biological invasions.