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Research article - Peer-reviewed, 2020

Estimating density from presence/absence data in clustered populations

Ekstrom, Magnus; Sandring, Saskia; Grafstrom, Anton; Esseen, Per-Anders; Jonsson, Bengt Gunnar; Stahl, Goran;

Abstract

Inventories of plant populations are fundamental in ecological research and monitoring, but such surveys are often prone to field assessment errors. Presence/absence (P/A) sampling may have advantages over plant cover assessments for reducing such errors. However, the linking between P/A data and plant density depends on model assumptions for plant spatial distributions. Previous studies have shown, for example, how that plant density can be estimated under Poisson model assumptions on the plant locations. In this study, new methods are developed and evaluated for linking P/A data with plant density assuming that plants occur in clustered spatial patterns.New theory was derived for estimating plant density under Neyman-Scott-type cluster models such as the Matern and Thomas cluster processes. Suggested estimators, corresponding confidence intervals and a proposed goodness-of-fit test were evaluated in a Monte Carlo simulation study assuming a Matern cluster process. Furthermore, the estimators were applied to plant data from environmental monitoring in Sweden to demonstrate their empirical application.The simulation study showed that our methods work well for large enough sample sizes. The judgment of what is' large enough' is often difficult, but simulations indicate that a sample size is large enough when the sampling distributions of the parameter estimators are symmetric or mildly skewed. Bootstrap may be used to check whether this is true. The empirical results suggest that the derived methodology may be useful for estimating density of plants such as Leucanthemum vulgare and Scorzonera humilis.By developing estimators of plant density from P/A data under realistic model assumptions about plants' spatial distributions, P/A sampling will become a more useful tool for inventories of plant populations. Our new theory is an important step in this direction.

Keywords

independent cluster process; intensity; Matern cluster process; plant monitoring; sample plots; spatial models; Thomas cluster process; vegetation survey

Published in

Methods in Ecology and Evolution

2020, volume: 11, number: 3, pages: 390-402
Publisher: WILEY

Authors' information

Umeå University
Swedish University of Agricultural Sciences, Department of Forest Resource Management
Swedish University of Agricultural Sciences, Department of Forest Resource Management
Swedish University of Agricultural Sciences, Department of Forest Resource Management
Esseen, Per-Anders
Umea University
Jonsson, Bengt Gunnar (Jonsson, Bengt-Gunnar)
Mid-Sweden University
Swedish University of Agricultural Sciences, Department of Forest Resource Management

UKÄ Subject classification

Ecology
Probability Theory and Statistics

Publication Identifiers

DOI: https://doi.org/10.1111/2041-210X.13347

URI (permanent link to this page)

https://res.slu.se/id/publ/104481