Brenda Hanley
Jennifer Peaslee
January 10, 2019

Understanding Reintroduction

Reintroduction of plants and animals by wildlife professionals into previously depopulated habitats is used to restore ecosystem function or maintain biodiversity. 


Bison herd on the move


Restoration ecologists regularly replant areas using seeds collected from host plants that grow in thriving areas, or from starts that have been nurtured in greenhouses.  Similarly, restoration ecologists gather healthy animals from one area or conduct captive breeding in zoos or other head start facilities to prepare for wild release of individuals in a desired area. 

But how do wildlife managers know how many individuals to release to create a successful, thriving population?  Should we release 5?  10?  500? What age groups (life stage) should they be and how many of each?

 Well, it’s complicated…because that’s just the way math is.

Defining Perspective

To answer this question, managers need to consider about 20 important perspectives.  Among these considerations is an assessment of the size of the restoration site in relation to the life history strategy.  Will a 5 square mile area hold a wolverine?  Probably not!  What about a population of mushrooms?  More likely!    

Managers must also assess the nutritional requirements of the species.  Will 5 square miles support the grazing needs of 30 bison?  Probably not!  Will 5 square miles support a population of salamanders?  More likely!        

Biologists also need to ensure that released plants and animals are not spreading disease.  The last thing we want to do while restoring a population is to inadvertently facilitate its decline!

These are only a few of the perspectives that must be considered when planning any reintroduction. All perspectives are important.

One important calculation can be made with nothing but a pen and paper.  Stable population theory specifies the proportion of individuals that need to exist in each stage of a life history in order for the overall population to grow in an (“asymptotic”) stable manner.

Pie chart image showing stable population proportions using the StaPopd App

StaPOPd App - Stable Population Dynamics

So back to our question.  How many of each life stage do we need to place into an area to ensure that our activities are immediately aligned with natural stable population dynamics (SSD)?  The StaPOPd app will help you figure that out!  Give it a try! 

StaPOPd graph showing time series based on a release in and out of Stable Stage Distribution

Reintroductions are complex. It is prudent to assess your reintroduction strategy from all perspectives. Among others, StaPOPd can be used in conjunction with individual-based models, such as Vortex (Lacy & Pollak,  2014) and others.

Happy planning!