Abstract Detail

On models and methods pertaining to plant reproduction

Tenhumberg, Brigitte [1].

The fate of seeds and its relevance to population dynamics.

This talk is concerned with two important processes affecting the fate of seeds: density dependence and seed bank dynamics. In both cases we used integral projection model where plant size is a continuous variable, and time is discrete. With increasing plant fecundity seed germination eventually becomes limited by the availability of micro sites rendering germination probability a function of seed density. Unfortunately, in many cases, the data to estimate germination over a range of seed densities is sparse and noisy. Following Occam’s razor principle researchers typically assume germination rate to be density independent (only a single parameter), without considering the effect of this structural uncertainty in model predictions. Using the endangered Penstemon haydenii as a case study we compare the predictions of a model assuming germination probability is constant with one where germination probability is decreasing with seed density. Both assumptions have equal statistical support (virtually same AICc-values). Asymptotically the DI model predicts population stasis (log λ≈0), while the DD model suggests a 30%chance that populations drop to unsutainably low numbers (<1 plant). However, the density dependent model predicts higher establishment probability following a dispersal event to a new location than the density independent model (transient dynamics). Despite the differences in model predictions both models come to similar management recommendations.
For many plant species seed bank dynamics are key for population persistence. This is especially true for disturbance specialist plants because seeds require a disturbance to germinate. Disturbances not only create more favorable environments for germination they also vertically redistribute seeds within the soil column. Redistribution in the soil is important because how deep a seed is buried in the soil influences its survival and germination probability. This tradeoff inspired agricultural scientists to explore optimal ploughing regimes. The insights gained from agricultural systems do not necessarily apply to disturbance specialist plants in natural environments because disturbances required for germination occur in a much more unpredictable fashion than those that occur in agricultural fields. As a criterion for population viability we use a quasi-extinction threshold defined as a seed density of 50 seeds. Our model predicts that increasing the disturbance frequency always increases the long-term population viability but the effect of mean depth of disturbance depends on seed survival in the seed bank and disturbance frequency.  These conclusions differ from optimal ploughing modes suggesting that conclusions from agroecosystems not always apply to natural systems.

1 - University of Nebraska, School of Biological Sciences and Department of Mathematics, 412 Manter Hall, Lincoln, NE, 68588-0118, USA

Keywords:
population dynamics
models
Penstemon haydenii
seed bank.

Presentation Type: Symposium or Colloquium Presentation
Session: SY09
Location: Summit/Boise Centre
Date: Wednesday, July 30th, 2014
Time: 8:45 AM
Number: SY09003
Abstract ID:124
Candidate for Awards:None