DOI: 10.5061/dryad.sbcc2fr8v
title: Differentiating spillover: an examination of cross-habitat movement

description: The movement of organisms between habitats is a fundamental process that
 occurs within all ecological disciplines. Once the organism has entered a
 recipient habitat, its behavior generates a movement pattern as it may
 remain, move on, return, or constantly move between, producing different
 population dynamics and environmental changes. Originally, “spillover” was
 one of these distinct patterns - the uni-directional movement from a donor
 habitat to a different, adjacent recipient habitat. However, ecological
 definitions of spillover have become overly generalized to include any
 cross-habitat movement. As spillover research has nearly doubled since
 2018, it is imperative to have universal nomenclature and methods that can
 quantify the term. This will allow us to advance our understanding of
 organism behavior in dynamic landscapes. To assess how spillover has been
 addressed within empirical literature, we reviewed 337 studies and
 organized them into the ecological disciplines of agriculture, disease,
 fisheries, and habitat fragmentation. Each study’s definition of spillover
 and the methods used to quantify the term was analyzed using four
 definition criteria that differentiates different cross-habitat movement
 patterns. We then determined the specificity of the definition and if the
 methods used matched the definition provided. Authors often define
 spillover as a movement (45%) but assess the location of organisms instead
 (96%). Additionally, 98% of studies assume direct movement out of the
 donor habitat, which can lead to an over-estimation of movement distance
 and spillover effect within the recipient habit. Overall, few studies
 (12%) included methods that matched their own definition, revealing a
 distinct mismatch. This was particularly noticeable within the fisheries
 discipline, likely the result of studies incorporating 1.5-fold more
 criteria within their definitions. There is much theory of the potential
 impact of organism movement, yet different movement patterns are often not
 differentiated empirically. Thus, the actual impact within natural systems
 is unclear. This ambiguity additionally limits communication and
 collaboration that need universal definitions and methodology. Techniques
 that quantify movement directly, such as tracking and
 capture-mark-recapture, are more suited to understanding effective
 long-term management implications and the impacts of disturbance on
 populations and communities.
description: We compiled a database of spillover studies that were found in
 the Web of Science (http:www.webofknowledge.com) records up to March 31,
 2021. We used the search terms “spillover” and “spill over”. We then
 excluded categories outside of the biology discipline (e.g., economic or
 chemical spillover) as well as human epidemiology literature, which uses
 language very distinct from ecological work. As the remaining publications
 included several hundred papers disparate from organismal spillover, we
 further refined our search using the terms “organism”, “biodiversity”, or
 “population”. Articles included in our database 1) specifically mentioned
 “spillover” or “spill over” within the text, 2) used living organisms as
 the propagule of movement, and 3) empirically assessed spillover or the
 consequences of spillover. In this way, we collected a broad spectrum of
 papers that included ecological, behavioral, evolutionary, applied, and
 basic science articles.
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