Review:
The idea that we could populate the Earth with any species and
that this would re-create an 'Eden' somewhere goes back to the
Acclimatisation Societies of the 19th century. Today, after
much (often painful) association with non-native species we
recognise invaders for what they are. Whereas this is often
to the detriment of the existing ecosystem it does provide us
with a way of studying population movements. Whether biomes
are the best place to try out experiments is another question
altogether but there is now a small but growing band of ecologists
who are specialising in this area and invasion ecology is now
a distinct topic in its own right.
Because
this is new, there is the initial problem of getting the terminology
right and demonstrating the parameters of the subject. This
is the aim of the first chapter here. That there are at least
27 different terms to cover essentially the same thing shows
how far we need to go to produce a synthesis that we can agree
with. To assist further, this chapter outlines the main process
of invasion and gives examples to illustrate this. To be an
invader you need to travel so it is no surprise to find this
as the topic of chapter two. A distinction is made early on
between the route (pathway) and mode (vector) of transport.
We get several examples to highlight this basic division. Vectors
are further investigated and the key ones (notably sea-based)
is described with cases ranging from the slave trade to 19th
century commerce. Given this increasing ease of movement it
is easy to see how, in chapter three, that the trend in invasion
is sharply upward. Wherever you look, and examples here span
the globe, the same trend is seen (suggesting, as others have
put it, to a homogenisation of ecology!). This shouldn't be
taken to be a blanket increase - temperate zones seem to have
more than their fair share (due presumably to the greater amount
of trade). Chapter four turns to the invader itself and shows
the parameters needed to be successful. It's not just a question
of being tough you also need the reception to be agreeable.
As chapter five notes, the best places are those where disturbance
has taken place e.g. fire, agriculture and, these days, global
warming. Once the non-native has reached a suitable abiotic
environment it needs to establish against the resident biota.
Although the title of chapter six suggests this is simple, the
real picture, as we see, is far from obvious with no strong
evidence for any particular model of success. One is left with
the impression that multiple causes are needed for success or
failure. Once the population becomes established there's a need
to see where it spreads. For plants this might be simple but
for animals it's far harder and so a key weapon is mathematical
modelling. As outlined in chapter seven we do get some idea
of rate and direction of spread. Non-native species are just
native species elsewhere so it should be possible to study them
using standard ecological concepts. This is the work of chapter
8 which describes the population models, dispersal patterns
and biotic interactions we can see in non-native organisms.
All this invading must have an effect on the resident ecology
and chapter 9 highlights some of the key findings such as extinction
and predation. Chapter 10 takes this one stage further to include
human reactions to invaders and how impacts can be measured
and therefore addressed. Chapter 11 complements this by looking
at invasion for the invaders perspective and describing the
possibilities of invaders evolving in their new habitat. Finally,
we look at assessing the risks and seeing how we can deal with
the invaders (if indeed it is cost-effective to do so.
This
is an excellent guide to the topic. It covers a significant
portion of the study and highlights all the key elements. The
aim of this text was to provide a broad overview and in this
it has succeeded. Although at this stage a little too complex
for secondary students it provides a very good foundation for
both theoretical and practical ecology. The focus on human impact
and management gives the book a far broader appeal and more
useful scope than the more usual ecological focus. Definitely
a key text in its field.