Modeling Markovian Dependence in Populations of Aralia Nudicaulis

Abstract

I examined spatial patterns of two populations of the clonal herb Aralia nudicaulis for evidence of spatial inhibition among neighboring ramets. Second—order spatial analysis revealed that ramet patterns of both populations were regular at local spatial scales, a result consistent with the proposition that localized, inter—ramet interactions are important in reducing spatial overlap. Localized ramet interactions suggest Markovian dependence, which is defined when an event (e.g., occurrence of a ramet) at X is dependent solely on the existence or otherwise of an event within a distance ° of X. Evidence of Markovian dependence in the populations was tested by fitting Markov point—process models to the observed ramet patterns. The populations conformed well to the Markov model, the results indicating that both ramet spatial patterns were Markov of range ° = 18 cm. This inhibition distance corresponds closely to the mean horizontal radius of an A. nudicaulis ramet, indicating that interactions occur at the spatial scale of the individual. I suggest that a likely mechanism for the development of locally regular spatial patterns in these populations in inter—ramet competition for a limiting resource, probably light.