Over three days we have posted a collection of blog posts on a topical Forum discussion published in Issue 2 about the methods used in wildlife conservation and in particular the role of dingoes in conservation. Following acceptance of a peer-reviewed Forum critique of another article in the Journal it is the Journal’s process to invite the original authors to write a peer-reviewed response to the critique. Both opinions are then presented side by side in an issue to enable readers to form their own opinions.
In this post Dale Nimmo talks about his recent Forum article ‘Dingoes can help conserve wildlife and our methods can tell’ written as a critique to a Practitioner’s Perspective from Matt Hayward and Nicky Marlow ‘Will dingoes really conserve wildlife and can our methods tell?’ Matt Hayward and colleagues responded to the Forum with their article ‘Ecologists need robust survey designs, sampling and analytical methods’.
Here you can read a post from Matt Hayward and a post from the Associate Editor, Jacqueline Frair and her postdoc Paul Schuette. (Please note that although the articles comment on each other the blog posts were received separately and are not intended as comments on the previous post.)
As with apex predators globally, debate regarding the role of dingoes in conservation has been underway for decades, but has recently intensified. Hayward and Marlow (2014) (herein ‘H&M’) added to this debate, questioning the science underpinning one particular finding: that dingoes can suppress introduced mesopredators, namely red foxes and feral cats, and in doing so can benefit native wildlife (that are heavily preyed upon by mesopredators). They caution against the use of dingoes to control foxes and cats when, in reference to those who advocate such an approach, they state that “it would be a brave conservation practitioner who leaps at the recommendations proffered”.
My colleagues and I responded to this article. Although there are several issues that we disagree on, both conceptual and methodological, discussion around the exchange (see here, here, and here) and a further response by Hayward and colleagues has narrowed in on the issue of sampling techniques for surveying carnivores. H&M argue that indices of abundances commonly used in carnivore research, such as track counts from trails, are unreliable as a proxy of abundance. As such, studies which use indices cannot be a reliable basis for management, and indices should be abandoned in preference of techniques that can estimate a species’ population density (e.g. distance sampling, mark-recapture).
While the way we measure a species’ abundance is central to this debate, it is wrong to view this as a debate about the merits of indices versus estimates of populations. In our response to H&M, we readily acknowledge that an estimate of abundance is, ideally, preferable to an index. Indices are often used due to cost and feasibility, not because they are the preferred method. Asking ‘which is better’ is like asking whether you would prefer to drive a Lada Niva or Porsche. Given unlimited funds, most people would prefer to drive a luxury vehicle, but as funds become more limited, the choices narrow. In the end, it’s better to have a humble vehicle that ‘gets the job done’ than going without altogether.
In our article, we show that there is ample evidence to suggest that, for a range of medium and large carnivores, indices often ‘get the job done’. Studies that correlate simple indices (e.g. such as the number of tracks counted along trails) with known population densities of carnivores often have very good explanatory power (e.g. explaining over 90% of the variance in actual abundances). Therefore, while we agree that validation of indices for dingoes, foxes and cats in Australia is required (as would be validation of population estimates), the balance of evidence is not sufficient to throw out the high quality work that has been undertaken on the positive effects of dingoes on Australian ecosystems (for examples see here, here, here, here, here, here, and here).
So how does this debate move forward?
If we regard estimation as the gold standard and indices as the poor cousin, then the use of indexation versus estimation is a tradeoff bound within the budgetary constraints of practitioners and researchers. Because the costs of indexation and estimation can vary (estimation, in general, is more costly than indexation, see here for example), this tradeoff will often come down to a decision to have more study sites with indexed abundance, or fewer sites with estimates of abundance. When this is the case, the decision to index or estimate will impact the power of studies to detect an effect of a given magnitude (such as the effect of dingoes on mesopredators and, in turn, native wildlife).
The next step then is to go beyond axioms and to answer, statistically, what are the costs of different methods of indexation and estimation, how do these impact our ability to detect a change in populations of a given magnitude (i.e. assuming various relationships between indices/estimates and actual density, and considering the impact on sample sizes), and most importantly, to what extent the use of one over the other would result in a tangible difference to management.