2.8 ESTABLISHMENT - SURVIVAL AND REPRODUCTION OF EXOTIC ORGANISMS IN A NEW ENVIRONMENT

Drawing on the work of Walford and Wicklund¹⁹ Walters²⁰has recently argued that:

The main factors which will determine the distribution of a species are the upper and lower limits of its temperature tolerance, the time period in which the ambient temperature is favourable for reproduction, and presence of a suitable environment.

Other variables affecting suitability of habitat for introduced organisms include salinity regimes, habitat, predators and food sources. If the physical properties of the new environment correspond sufficiently with those of the original ones, the introduced species may well survive and multiply²¹

She adds (based on Drake²² that the invasion success of a species will, in reality, depend on much more than simple matching of organism characteristics with a favourable physical environment:

...the mechanics of community assembly are very important. It has been shown that different invasion sequences can lead to the formation of alternative community states, and that the competition between communities and within any community is directly controlled by assembly history, particularly in terms of the strength of competitive interactions, the outcome of these and the identity of the competitors. The physical environment may also be influenced in different ways by these interactions. This helps to explain why an introduced species may be very successful in one system but fail in another which is physically very similar.

Walters concludes that just because a species may have been unsuccessful in establishing populations in the past does not mean that it will not do so in the future. Conditions may differ and a niche may become available at a later time.