Diagnosing decline

When should managers step in to stop an animal from becoming extinct? An obvious answer is that something
should be done when the population is experiencing a significant decline. But how can you distinguish between
declines that are the result of human pressure as opposed to declines that are merely a part of the population’s natural
fluctuations?

Martina Di Fonzo and colleagues have worked on this very issue and believe they have an answer (Di Fonzo et al., 2013).
They simulated typical mammalian population time-series under different human pressure types and intensities and
identified significant distinctions in population dynamics. Based on the concavity of the smoothed population trend and the algebraic function which was the closest fit to the data, they determined those differences in decline dynamics that were consistently attributable to each pressure type.

They then applied their newly developed method to 124 wildlife population time-series and investigated how those threat types diagnosed by their method compare to the specific threatening processes reported for those populations. They were able to show that wildlife population decline curves can be used to discern between broad categories of pressure or threat types, but do not work for detailed threat attributions. More usefully, they found that differences in population decline curves can reliably identify populations where pressure is increasing over time, even when data quality is poor. So, here is a cost-effective technique for determining whether the decline being witnessed is a decline we should be worrying about.

Reference
Martina Di Fonzo Ben Collen & Georgina M. Mace (2013). A new method for identifying rapid decline dynamics in wild vertebrate populations. Ecology and Evolution 3: 2378-2391.

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