Objective:

A broad objective of the Sevilleta LTER is to understand the trajectories of ecosystem transition zones under current and future climate scenarios. The WAVE model provides a quantitative framework for combining demographic responses to climate, interspecific interactions, and seed movement to determine the direction and pace of change at ecotones between foundation plant species.

Novelty:

State transitions are often studied at the ecosystem scale without explicit consideration of the lower-level process that give rise to ecosystem-level phenomena. The WAVE model captures the building blocks of state transitions — births, deaths, and movements of foundation species — and can integrate with TECO to link demographic processes with ecosystem-level process outcomes

Design:

The WAVE model is based on integrodifference equations, which have a long history in spatial ecology. These models predict the growth of populations in space and time based on the combined effects of demography (which determines change in local density) and dispersal (which determines the spatial redistribution of propagules). The WAVE model couples the dynamics of two foundation-species populations, generating a collision ecotone where they intersect. The trajectory of the ecotone — whether it persists stably or moves directionally, with one species invading the other — depends on the combined effects of local density-dependent demography (intra- and inter-specific interactions) and seed dispersal. The WAVE model is designed to accommodate data inputs from results of our Mean – Variance Experiment, allowing us to predict ecotone dynamics under climate scenarios with altered mean and variance of soil moisture.

Circles denoting foundation species A and triangles denoting foundation species B occupy a gradient from A only to B only. In the middle the symbols are interspersed with each other, and arrows pointing between the two represent recruitment, competition and dispersal.

The WAVE model provides a quantitative framework for combining demographic responses to climate, interspecific interactions, and seed movement to determine the direction and pace of change at ecotones between foundation plant species.

Responses:

The WAVE model predicts the velocities of expansion/contraction for two foundation plant species at their ecosystem transition zone. From these velocities, we can derive estimates for ecotone stability or the direction and pace of transition.