Search Results for author: Evan Johnson

Found 5 papers, 3 papers with code

Explaining mountain pine beetle dynamics: From life history traits to large, episodic outbreaks

no code implementations19 Dec 2023 Evan Johnson, Mark Lewis

However, two life history traits -- MPB's size-dependent fecundity and preference for large trees -- are responsible for 25% of the peak number of beetles.

Coexistence in spatiotemporally fluctuating environments

no code implementations20 Jan 2022 Evan Johnson, Alan Hastings

Ecologists have put forward many explanations for coexistence, but these are only partial explanations; nature is complex, so it is reasonable to assume that in any given ecological community, multiple mechanisms of coexistence are operating at the same time.

Resolving conceptual issues in Modern Coexistence Theory

1 code implementation20 Jan 2022 Evan Johnson, Alan Hastings

This can be accomplished in three steps: 1) relating the construct of coexistence to invasion growth rates, 2) mathematically partitioning the invasion growth rates into coexistence mechanisms (i. e., classes of explanations for coexistence), and 3) relating coexistence mechanisms to simple explanations for coexistence.

Misconceptions

Towards a heuristic understanding of the storage effect

1 code implementation18 Jan 2022 Evan Johnson, Alan Hastings

Our approach focuses on dividing one of the key conditions for the storage effect, covariance between environment and competition, into two pieces, namely that there must be a causal relationship between environment and competition, and that the effects of the environment do not change too quickly.

Methods for calculating coexistence mechanisms: Beyond scaling factors

1 code implementation17 Jan 2022 Evan Johnson, Alan Hastings

Here, using theoretical arguments and case studies, we compare four such methods for calculating coexistence mechanisms: 1) Scaling factors, the traditional approach where resident growth rates are scaled by a measure of relative sensitivity to competition, obtained by solving a system of linear equations; 2) The simple comparison, which gives equal weight to all resident species; 3) Speed conversion factors, a novel method in which resident growth rates are scaled by a ratio of generation times, and; 4) The invader-invader comparison, another novel method in which a focal species is compared to itself at high vs. low density.

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