Lecture 2
Key Ideas and take Home Messages
(1) Defining invasive and invasion is hard.
(2) Most agree that there are some key differences between the natural processes of
range expansion and dispersal.
- Rate of arrival
- The crossing of biogeographical barriers independent of species
biology / ecology / physiology.
- In other words, humans are bridging natural limitations on range
boundaries and moving species incapable of moving themselves and
doing so at a frequency far greater than such events occur naturally
(3) Invasion process
A stepwise process that removes species through a series of filters between
each transitional step (Transport – Establishment – Spread – Impact)
The original pool of species becomes progressively smaller as species fail to cross
each of the filters so that only a few species go on to become what we’d think of as
important invaders.
(4) Invasion models
- Reaction-diffusion has a time and space component. Species increases its
range while simultaneously increasing its population density. Range
expansion is limited by the species own capability of dispersal
- Human vectored – Humans move individuals from the founder population
beyond the limitations of the species own dispersal capability to create new
population foci.
- Stratified – incorporates both processes. The result is a coalescing of
populations expanding through their own dispersal with those created by
human aided long distance transport.