Wednesday, August 8, 2007

PS 51-169: Elevated recruitment of zebra-tailed lizards (Callisaurus draconoides) in Joshua Tree National Park following an El Niño – Southern Oscillation event

Marina M. Gerson, California State University, Stanislaus

  • Disturbance events influence community structure and the biology of affected populations. Moderate disturbances during mid-successional stages may halt the process of succession or return the ecosystem to an earlier stage. While the immediate effect of a disturbance event may include local damage, in the long term, the result may be more persistent community structure. In the eastern Pacific Ocean, cyclical El Niño–Southern Oscillation (ENSO) events result in elevated levels of precipitation and subsequent disruptions to local communities including in arid regions. With the increased availability of water in desert lands, food may be more abundant for animals, resulting in population growth; ENSO events may contribute to the persistence of populations in these harsh environments. I documented the relative abundance of juvenile zebra-tailed lizards (Callisaurus draconoides), in populations in Joshua Tree National Park, California, USA, following the 1997-98 ENSO event, during which rainfall levels were double the regional average. C. draconoides were collected in 1999 and 2000. Chi-square analysis showed that juveniles were relatively abundant in the population in 1999 following the ENSO event compared to year 2000 (64.6% compared to 13.6% juveniles; χ2= 210.75, p<0.000001, df =1). In 1998, C. draconoides experienced abundant food resources. It appears that the increased primary productivity in 1998, a result of the increased rainfall during ENSO conditions, led to increased recruitment of C. draconoides, which were then present as juveniles in 1999. This could have been achieved through: greater numbers of reproducing females, larger clutches, multiple clutches, and/or greater survival of hatchlings. Desert populations may rely on sporadic years of elevated recruitment to maintain population sizes in the long term. Given that ENSO events have been documented for at least the past 124,000 years, these short-term climate changes may have had a significant influence in shaping current community composition and structure.

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