Evolutionary consequences of niche construction and their implications for ecology

Abstract

Organisms regularly modify local resource distributions, influencing both their ecosystems and the evolution of traits whose fitness depends on such alterable sources of natural selection in environments. We call these processes niche construction. We explore the evolutionary consequences of niche construction using a two-locus population genetic model, which extends earlier analyses by allowing resource distributions to be influenced both by niche construction and by independent processes of renewal and depletion. The analysis confirms that niche construction can be a potent evolutionary agent by generating selection that leads to the fixation of otherwise deleterious alleles, supporting stable polymorphisms where none are expected, eliminating what would otherwise be stable polymorphisms, and generating unusual evolutionary dynamics. Even small amounts of niche construction, or niche construction that only weakly affects resource dynamics, can significantly alter both ecological and evolutionary patterns.

Figure 1

(a) Positive niche construction, independent renewal, and no external selection (R_t = λ₁R_t−1 + λ₂p_t + λ₃, γ = 0, α₁ = β₁ = α₂ = β₂ = 1, r = 1/2, n = 1). Here, the only selection is that generated by the resource. The arrows represent the trajectories of a population, the heavy line represents stable equilibria, and the dashed line represents unstable equilibria. The direction of selection generated by the resource switches at R = 1/2. In b–d, with independent renewal and external selection favouring allele A, niche construction generates selection that may oppose the external selection, taking populations to alternative equilibria and generating polymorphisms. b and c show positive niche construction (R_t = λ₁R_t−1 + λ₂p_t + λ₃, γ = 0), with weak selection (α₁ = β₁ = 1, α₂ = 1.01, β₂ = 0.99, r = 1/2) (b), and strong selection (α₁ = β₁ = 1, α₂ = 1.1, β₂ = 0.9, r = 1/2) (c). d shows negative niche construction, independent renewal, and external selection favoring allele A (R_t = λ₁R_t−1(1 − γp_t) + λ₃, λ₂ = 0, α₁ = β₁ = 1, α₂ = 1.1, β₂ = 0.9, r = 1/2). When selection favors allele A and ɛ is negative, positive niche construction (γ = 0) (e) and negative niche construction (λ₂ = 0) (f) generate polymorphisms (α₁ = β₁ = 1, α₂ = 1.1, β₂ = 0.9, r = 1/2).

Figure 2

Positive niche construction, independent renewal, and heterozygote advantage (R_t = λ₁R_t−1 + λ₂p_t + λ₃, γ = 0, α₁ = α₂ = 0.99, β₁ = β₂ = 0.9, r = 1/2, n = 1). Provided r is not very small, populations converge to a single equilibrium in linkage equilibrium, the position of which may be strongly affected by niche construction. The + represents the equilibrium in the absence of niche construction. By increasing R, niche construction changes the frequency-dependent component of genotype fitnesses, affecting the equilibrium frequency of allele A. In both a and b, without niche construction, allele a would be fixed, whereas in a, niche construction allows A and a to coexist, and in b, niche construction drives A to fixation.