Synchronous variation and long-term trends in two populations of black rat snakes

P. J. Weatherhead, G. Blouin-Demers, K. A. Prior

Research output: Contribution to journalArticlepeer-review


Synchronous variation among animal populations affects the vulnerability of endangered species and is relevant to understanding population fluctuation generally. We analyzed data collected over 18 years from two populations of black rat snakes (Elaphe o. obsoleta), a species of conservation concern in Canada, to determine whether the populations varied synchronously. Because the populations were 30 km apart and genetically distinct, synchrony should be attributable to common stochastic environmental factors, the Moran effect. Synchronous variation in annual estimates of population size, survival probability, recruitment, and age structure all provided evidence of a Moran effect. However, opposite trends in age structure through time suggested that the internal dynamics of the two populations were different. The conservation implication of synchrony is that this population of rat snakes is vulnerable to stochastic environmental phenomena because all subpopulations could become rare simultaneously. Evidence of different population processes in the two populations suggests, however, that local factors may be of more immediate relevance to conservation than regional phenomena. More generally, these results indicate that evidence of synchronous variation in population size and similar long-term population trends - both populations appeared to be declining - are not necessarily indicative of common underlying population dynamics.

Original languageEnglish (US)
Pages (from-to)1602-1608
Number of pages7
JournalConservation Biology
Issue number6
StatePublished - Dec 2002

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Nature and Landscape Conservation

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