Ian Hatton, a McGill PhD grad, might have stumbled upon a new natural law while trying to make sense of the small lion numbers in Africa.
Until now, the theory went that predator numbers fluctuate according to the density of prey. Meaning that environments with a rich pray population must also support large numbers of predators, since they offer an abundant source of food. But things are not that simple, Hatton and his colleagues found.
Ian Hatton noticed that despite the fact that Africa’s national parks offer a wide variety of prey in significant numbers – such as gazelles, zebras or water buffalos – the lion population wasn’t increasing accordingly. Hutton and his team proceeded to look at hyenas, leopards and other predator’s. Everywhere the pattern held: the number of carnivores was too small relative to the number of animals they prayed on.
After analyzing data collected in over 1000 nature studies from the last 50 years, Hatton and his team published an explanation of this phenomenon in the latest issue of The Science journal.
Their conclusion was that regardless of environment predator populations are dependent on the prey’s rate of reproduction. Not on the absolute numbers of potential prey, as previously thought. Likewise, herbivores produce fewer offspring in crowded environments, since the competition for food is high. This makes both predators and prey rates of reproduction ultimately dependent on the eco-system’s crowding.
The model had been observed to apply with almost mathematical precision to every eco-system studied. According to scientists, the discovery is far more significant than it would appear at first sight.
Similar scaling laws are known to govern various functions of an individual body, but scientists weren’t previously aware of this type of pattern applying to whole eco-systems.
Jonathan Davies from the Department of Biology at McGill finds an analogy between Hatton’s model and cell division in mammals. Just like herbivore reproduction slows down with crowding (and lion numbers follow suit), so do cells in large animals divide themselves less often than in smaller animals, who’s cells are less… “crowded”.
“It seems that some basic processes reemerge across levels of organization, but we do not yet fully understand which ones and why.”
According to Michel Loreau of the French Centre national de recherché scientifique, Hatton’s discovery might form the basis of a new natural law. One that may govern both the individual organism and the bigger natural system he is a part of.
Photo Credits: commons.wikimedia.org
