Friday, July 3, 2015

Subsidized predators

The Rocky Mountain Elk Foundation has a magazine titled Bugle.  They write about all of the things you would expect and a few things that might surprise you.  For instance, they highlight scientific research on the nutrition and population dynamics of elk.

One of the research efforts that they reported involved the effects of bear predation on elk fawns.

Traditional predator-prey models are hard-wired to make it impossible for the predator to drive the prey into extinction or expatriation.  The model holds that predator populations lag the prey population during the growth phase and then decline more steeply after the peak is reached.  That last few prey are widely dispersed and cannot be hunted efficiently by the predator.  The rabbit always has too many brush piles for the weasel, fox or owl to hunt effectively.

This model falls apart when the "predators" are opportunistic omnivores or a generalist carnivores.

Omnivores have many food sources they can draw upon.  In many cases, the carnivore portions of their diet are targets of opportunity.  It is a chance to gain a choice morsel of fat and protein.  Day-in and day-out, the majority of calories may come from plant based food sources with low nutritional density.  It is enough to keep them alive.  But meat....ah, that is a party.

The dynamics of omnivore populations can result in a region being saturated of opportunistic predators such that reproductive success is driven to zero.


Nearly all birds are omnivores.  In many cases, even the ones that are nominally herbivores feed their fledglings a significant amount of bugs.  Growing young need food with high calorie and protein density.  Yellow sorrel seeds don't make the grade.  They need bugs.

In theory, one way to increase bird predation of pestiferous Colorado Potato to put a bird feeder in the center of the garden.  The availability of bird seed (sunflower seeds are readily accepted by a large number of common birds) "pays" for the birds' trips to the garden.  And, while they are there, they just might snack on a few undesirable bugs.  I might quickly tire of picking potato beetles, but they are bite sized bars to little brown birds.  They don't get tired.

Think about it.  You probably would not drive to the grocery store to buy a single candy bar.  But you probably look them over while you are waiting in the check-out line and it is pretty easy to buy one when it is simply a matter of reaching out your hand.

I will report later on how this plays out.


  1. I will be curious to see how this plays out... Sorry you're having to go thru this...

  2. I will be curious to see how this plays out... Sorry you're having to go thru this...