Large populations can be vulnerable too
Animal populations may be more vulnerable to factors like environmental change and harvesting than previously thought, a new theory on population growth suggests.
An international study in the journal Science today analyses data on mammals, birds, fish and insects to come up with a surprising new mathematical equation of how animal populations are regulated.
The research answers long standing questions about whether the size of a population can affect its growth rate, scientists including Australian researcher, Dr Jim Hone of the University of Canberra, write.
Scientists have assumed a linear relationship between population density and population growth, says Professor Frank Carrick of the University of Queensland.
But this study turns conventional theory on the head by showing a 'concave' relationship between density and growth.
In other words, growth represents a curve where populations are most vulnerable at the top and bottom extreme of the curve and most stable in the middle.
"One of the most used approaches to modelling populations and making predictions about them is the logistical equation that assumes a linear relationship between growth rate and density," Carrick says.
"So as each new animal arrives the effect on the others is the same as the population grows. That assumes the relationship between population increases and the number of animals is the same no matter how many animals are there.
"But [this study shows] if population density is very or very high then you might get a different outcome."
Carrick says the research confirms what ecologists have long suspected, that current methods of estimating the impacts of human and environmental factors on animal populations are simplistic.
Implications for whaling
The findings have major implications for practices such as whaling, Carrick says.
If the effect on the whale population is much more marked when it's trying to recover, which it is, then whaling based on conventional estimates of sustainability may have a dramatic effect, he says.
"The flip side is that for an animal population that's up near its carrying capacity, if you had a small change in the environment that can then have a really dramatic impact."