Invasive species use landmarking to find love in a hopeless place

Thursday, March 12, 2015

Prof. Kim Cuddington with model of a silver carp.Kim Cuddington, a Biology professor in the Faculty of Science, demonstrates how landmarking works and the key role it plays in population control for both conserving endangered species and controlling invasive species. 

Her study was published in Theoretical Ecology.

In 2013, she showed that only ten Asian carp are needed to establish a population in the Great Lakes.

This species will have a huge impact on the food web,” says Cuddington, a specialist in theoretical and population ecology. “Not only is it a fast-growing fish physically, but the population itself grows very quickly. A female can lay well over a million eggs a year."

But if there are so few individuals initially, how do they find a mate and create an ecological disaster?

It pays to do the math

Asian carp, butterflies and several other species find their mates by congregating at easily identifiable locations such as the area’s tallest tree or mountain. This highly efficient mate finding strategy known as “landmarking” allows species to reproduce even when population densities are impossibly low.

To understand how landmarking works, Cuddington uses a branch of math called combinatorics, the most famous example of which is the birthday problem – how many people do you need before you have two people with the same birthday (the answer is 23). 

Landmarking works the same way: What is the probability of a male finding a female at a fixed number of sites? The more prominent and rare the location is, the greater the chance a male will meet a female.

For example, if there are ten bars in town, your chance of meeting a mate is 10 per cent. But if there is only one bar in town, your chance of meeting that mate is 100 per cent.

A tool for endangered and invasive species

Cuddington found landmarking can play a key role in how we approach population control – for both conserving endangered species and controlling invasive ones.

More importantly, her research highlights how landmarking cannot be managed intuitively.

For example with an endangered species, if the number of landmarked sites is increased, the individuals will have a lower chance of finding a mate. In contrast, decreasing the number of landmarked sites in an effort to keep invasive species from reproducing has the opposite effect, and ensures individuals have a near certain chance of finding a mate.

In the case of the Asian carp, these species use river water quality and flow rate as landmarks and can therefore find a mate more easily than originally thought.

According to Cuddington, when particularly damaging invasive species such as Asian carp uses landmarking, officials need to worry.

For species like Asian carp, precautionary measures have to be extraordinary to prevent establishment in the Great Lakes,” says Cuddington.

Science in the mediaThis story has appeared in the following news outlets: 

  • Forbes, "Asian carp and the birthday problem" 
  • Radio Canada International, "Just a handful of invasive Asian carp could threaten Great Lakes"