Temporal scaling of episodic point estimates of seed predation to long-term predation rates


Correspondence author. E-mail: asdavis1@illinois.edu


1. Post-dispersal seed predation influences plant population dynamics in many terrestrial ecosystems, including weeds in arable systems, the focus of this study. Simulation models of management effects on weed demography require estimates of long-term seed predation as input, yet extremely rapid seed losses to predators force most measurements of weed seed predation rates to be made at a daily time-scale.

2. We compared several models for estimating inline image, the annual proportion of weed seeds consumed by granivores, from repeated short-term seed predation measurements. Competing models differed in duration of seed exposure to predators and weighting of short-term predation rates by concurrent seed rain. Verification data were obtained from field studies at experimental locations in Germany and the USA in which parallel measurements of short- and long-term weed seed predation were made in cereal crops.

3. Robust predictions of inline image were given by a model that exposed seeds to predators for two 48-h predation intervals, with no weighting of predation rates by seed rain. Model performance was consistent across locations, years, weed species and predator type. Resampling indicated that high temporal sampling intensity was critical to model performance and should be prioritised over high levels of spatial replication.

4. Estimates of inline image made from our experimental data and 10 published time series of short-term weed seed predation rates followed a normal distribution with μ = 0·52 and σ2 = 0·05. Additional work is necessary to assess applicability of the predictive model to seed predation time series from natural systems.

5.Synthesis and applications: Our results demonstrate that annual rates of weed seed predation may be reliably predicted from repeated short-term predation measurements. Predicted values may then be used in applied demographic models. At a more fundamental level, these results indicate that weed seed predation in arable fields is an episodic process, in which newly dispersed seeds are subjected to brief, intense predation, after which they become unavailable to granivores because of burial. Future efforts at managing agroecosystems to promote weed seed predation may benefit by viewing the process as dynamic and ephemeral.