Spatial niche packing, character displacement and adaptive 
speciation in an environmental gradient

Ferenc Mizera & Geza Meszena

Department of Biological Physics, Eotvos University
Pazmany Peter setany 1A, H-1117 Budapest, Hungary
Collegium Budapest, Institute for Advanced Study
Szentharomsag ter 2, H-1014 Budapest, Hungary
mizera@colbud.hu, geza.meszena@elte.hu

Evolutionary Ecology Research 5: 363-382 (2003)

Abstract

Ecology and adaptive dynamics of an asexually reproducing population,
migrating along an environmental gradient, is investigated. The living
conditions are optimal at the central location and deteriorate
outwards. The different strategies are optimized to the ecological
conditions of different locations. The control parameters are the
migration and the tolerance of the strategies toward the environmental
condition (location). Locally, population growth is logistic and
selection is frequency-independent, corresponding to the situation of
a single limiting resource. Behavior of the population is modeled by
numerically integrated reaction-diffusion equations as well as by
individual-based simulations. 
Limiting similarity, spatial niche segregation and character
displacement are demonstrated, analogously to the
resource-heterogeneity based niche partitioning. 
Pairwise invasibility analysis reveals a convergent stable singular
strategy optimized to the central, optimal location. It is
evolutionary stable if the migration rate and the tolerance are
large. Decreasing migration or decreasing tolerance bifurcates the
singular strategy to an evolutionary branching point. Individual-based
simulation of evolution confirms that, in the case of branching
singularity, evolution converges to this singular strategy and
branches there. Depending on the environmental tolerance, further
branching may occur. The branching evolution in the asexual model is
interpreted as a sign that the ecology of an environmental gradient is
prone to adaptive geographic speciation.