212 Monitoring Threatened Species and Ecological Communities
monitoring programs and some analytical tools to support implementation. It then
discusses a couple of key challenges in monitoring design – what to monitor and
how much to spend, again with a focus on tools to help answer these critical
questions.
Why monitor?
Possingham et al. (2012) identify five reasons to monitor ecosystems: knowing the
state of a system; understanding the way a system works; raising awareness about
an issue; engaging the public and leveraging effort; and serendipitous discovery of
threats or opportunities. Each of these objectives involve decisions and trade-offs
that can be complex and daunting. It is not always clear what should be measured,
how it should be measured, and which objective should be prioritised. Fortunately
there are tools to help and example applications to draw on.
Measuring the state of the system
In the context of threatened species conservation, knowing the state of the system
usually equates to estimating population size or population growth rate of a
species, or measures of the prevalence or intensity of a threat (e.g. Johnson et al.
1997; Hauser et al. 2006). Understanding the state of a system supports decisions
such as whether to conduct weed or predator control, bring individuals into captive
breeding, or actively manage human pressures depending on how a population is
faring or a threat is growing (Box 16.1).
Learning about the system to make better decisions
Ecological systems within which conservation of threatened species takes place
are complex. Monitoring is often required to learn about what drives changes in
abundance and distribution of species and to support predictions about how a
species will respond to management. In many instances, the ecological dynamics
that inf luence the success of management are complicated. For example, in some
areas of Australia, introduced predators prey mainly on rabbits – another
introduced pest species. When the rabbit density falls below a threshold, they may
switch to preying on less abundant native species (including threatened species)
(Molsher et al. 1999). Understanding these dynamics and learning about the
threshold abundance at which switching occurs is important because it
determines when managers should increase predator control in response to
changes in rabbit abundance.
Monitoring to learn about how species respond to threats, management or
environmental change has a long history in Australia (e.g. Chapters 21, 32). There
are many examples in which the benefits of learning are well understood, and these
examples can be used as templates for future attempts to design and justify the