Corresponding author: Mark Williamson (
Academic editor: Ingolf Kühn
As members of the editorial board of Neobiota who, for various reasons, didn’t get our names on the original editorial (
Three areas that we would like to stress are the interaction between invasion science and economics and the role that invasion science should play in advancing pure ecology in two areas, population dynamics and ecosystem ecology. Neither ecology nor economics appears as a word in the original bullet list, but many of the topics are obviously ecological while none are obviously economic. For economics, we want to point out its relevance to invasion science and the feedback between the two disciplines, particularly in a rapidly changing world with powerful new emerging economies. For ecology, we want to emphasise not what ecology tells us about invasions but what invasions reveal about ecology and evolution at two scales.
There are two recent multi-author books that show the extent and variety of the interaction of economics with invasion science (
The ecological and economic dimensions of the problem of invasive species are connected at different levels. Many of the changes that lead ecosystems to be more vulnerable to the impact of invasives (e.g. fragmentation, disturbance, loss of diversity, pollution) are direct consequences of economic behaviour. The ecological mechanisms affecting invasives, such as functional diversity and dispersion, are correlated with trade, transport and travel. The consequences of the reduction in ecosystem functionality and the ability to provide ecological services have direct implications for the value of the output and ecological capital of the system.
At every level, the ecological impacts of economic activities are incidental to and usually ignored by the actors concerned. These impacts are externalities of the market transactions; they are not taken seriously by those making the transactions perhaps because they are not held legally responsible for the impacts nor are the markets directly affected by these impacts. Instead these impacts are often borne by those who receive little or no benefit from the market transactions. In addition, quantifying some ecosystem services (and disservices) is difficult and approaches to do so vary necessarily by scale, type of service, and region (
The intimate relation between ecology and invasion science is well known. Less recognised is that invasions throw light on some ecological processes that can be more difficult to study in uninvaded systems. Many ecosystems are close to equilibrium or are following a moving equilibrium from seasonal or longer changes which makes detecting significant changes a long-term prospect and out of sync with two to four year funding cycles. Invasions supply ample examples of unintended experiments with systems well away from equilibrium, often over relatively short time periods. The resultant changes are informative both for the population dynamics of individual species and for the coevolution of communities.
In population dynamics, the growth and spread of populations are natural aspects to study in invaded systems. We will just mention two aspects, lag and the pattern of spread.
There is much misunderstanding of lag. It occurs when a population is not growing in numbers at all. When there are, as so often, casuals, i.e. individuals not producing population growth, it can be difficult to be sure whether the population is growing or not. A common problem is to mistake the early stages of logarithmic or quadratic growth with lag. The quickest solution is usually to plot transformations, e.g. log or square root, of the species counts. Too many statisticians want arithmetic plots which frequently conceal the behaviour of a population. Lags are important for management as they result in invasive species that appear to be harmless, sleeper weeds and such, leading to a lack of action when it would still be relatively cheap and easy to control or even eradicate a population. The lengths of lags are surprisingly variable and some can be quite long.
It is easy to suggest causes for lag, such as the wrong habitat at introduction, the wrong genotype first introduced or Allee effects, but we know of very few cases when the cause can even be guessed let alone demonstrated. One such is in
Conversely, spread is often quite easy to study though here again some biologists have made an elementary mistake, namely regarding the increase in records as an increase in population size, while nearly always it is only a measure of population range. Possibly this comes from models of spread involving population parameters such as the intrinsic rate of natural increase. Long term records of the ranges of invading species show much variation in the rate and pattern of spread, phenomena complicated by the heterogeneity of natural systems (
The other ecological topic we would like to mention is that species invasions may help us to better understand the mechanisms which generally govern ecosystems. How does co-evolutionary history among species shape the diversity, functioning and stability of ecosystems? Although this topic is somewhat related to the bullet point “Eco-evolutionary feedback between invasive traits and ecosystem function” in the original list, it focuses on different processes.
Interactions among plants, herbivores and microbes influence ecosystem functions (