Using space‐for‐time substitution and time sequence approaches in invasion ecology

Abstract

Summary 1. Invasion biologists use two main approaches to evaluate the effects of non‐native species (NNS) on diversity of native species (DNS), namely space‐for‐time and time approaches. These approaches have pitfalls related to lack of controls: the former lacks pre‐invasion data, while the latter often lacks data from non‐invaded sites. 2. We propose a framework that combines space‐for‐time and time approaches and which should result in more focused mechanistic hypotheses and experiments to test the causes of invasibility and the effects of NNS on DNS. We illustrate the usefulness of our framework using two case studies: one with the submersed macrophyte, Hydrilla verticillata, in reservoir and the other with the fish, Geophagus proximus, in a large river–floodplain system. 3. Hydrilla verticillata invaded sites with DNS similar to that found in non‐invaded sites, indicating that biotic and/or abiotic factors did not influence invasion success; however, DNS increased over time in invaded sites compared with non‐invaded sites, suggesting that H. verticillata facilitated natives. In contrast, G. proximus invaded sites with higher DNS than non‐invaded sites, suggesting that biotic and/or abiotic factors favouring natives were important for invasion success, but DNS increased in invaded and non‐invaded sites over time, indicating that an independent factor contributed to DNS increases. 4. Conclusions from both studies would have been inaccurate or incomplete if the space‐for‐time and time approaches had not been used in combination as proposed in our framework.

Are the effects of an invasive crayfish on lake littoral macroinvertebrate communities consistent over time?

“…Even though it is evident that temporal context should be included in studies of species invasions, comparisons of results from short-term studies with empirical data collected over multiple years are rare (Strayer et al, 2006;Thomaz et al, 2012). Due to the often cryptic spread and establishment of non-native species, and the limited availability of long-term monitoring datasets, establishing field studies that include data prior to invasions is difficult.…”

“…Due to the often cryptic spread and establishment of non-native species, and the limited availability of long-term monitoring datasets, establishing field studies that include data prior to invasions is difficult. Hence most empirical studies have used a space-for-time substitution approach whereby invaded sites are compared with non-invaded sites, with the underlying assumption that temporal and spatial variations are equivalent (Pickett, 1989;Thomaz et al, 2012). That design certainly has limitations; for example, systematic differences in environmental features between invaded and non-invaded areas might be the actual cause of the differences which are interpreted as effects of the non-native species (Thomaz et al, 2012).…”

“…Hence most empirical studies have used a space-for-time substitution approach whereby invaded sites are compared with non-invaded sites, with the underlying assumption that temporal and spatial variations are equivalent (Pickett, 1989;Thomaz et al, 2012). That design certainly has limitations; for example, systematic differences in environmental features between invaded and non-invaded areas might be the actual cause of the differences which are interpreted as effects of the non-native species (Thomaz et al, 2012). Therefore Thomaz et al (2012) and Dornelas et al (2013) suggested that a time approach with pre-and postinvasion data from the same area should be used together with a space-for-time design for more reliable assessment of effects.…”

“…That design certainly has limitations; for example, systematic differences in environmental features between invaded and non-invaded areas might be the actual cause of the differences which are interpreted as effects of the non-native species (Thomaz et al, 2012). Therefore Thomaz et al (2012) and Dornelas et al (2013) suggested that a time approach with pre-and postinvasion data from the same area should be used together with a space-for-time design for more reliable assessment of effects. However, in the absence of pre-invasion data, this is not possible.…”

Control of Invasive Plants: Ecological and Socioeconomic Criteria for the Decision Making Process

“…Some initiatives to assess and categorize invasive species based on their performance in the new range (impact) have been presented (e.g. Hiebert & Stubbendieck (1993) in the USA; Colautti & MacIsaac (2004); Khuroo et al (2008) in India; Thomas et al (2012) in Brazil). All these initiatives, practical issues related to biological invasions (Cronk & Fuller 1995;IUCN 2000;CBD 2000;Davis & Thompson 2000), an invader must have an undesirable impact on its new environment, whether economic, health, or ecological.…”