Interspecific Competition Between Monochamus titillator and Dendroctonus frontalis

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Abstract
Interspecific competition was hypothesized to exist as a result of foraging by Monochamus titillator Fabricius in the sub-cortical region of loblolly pines attacked by Dendroctonus frontalis Zimmerman. The existence of the interaction was demonstrated experimentally; first by defining the distributional pattern of D. frontalis progeny adults in samples of bark in which M. titillator foraging was absent. Next, using data in which foraging occurred the observed number of D. frontalis inside the foraged area was compared with the expected number if no foraging were present. The observed and expected values were demonstrated to come from different distributions which substantiated the existence of competition. The specifications for developing mathematical models of the competitive process included consideration of the extent and distribution of M. titillator foraging over the entire bole of the tree and D. frontalis density in the infested portion of the tree bole. The form of the data used in model development was appraised from the standpoint of providing the most realistic account of the process under consideration and the results of the use of unmanipulated data were compared with 2 separate types of manipulations commonly employed in the analysis of bark beetle populations. A series of nonlinear mathematical models based on unmanipulated data was developed which provides the expression of mortality resulting to D. frontalis as a consequence of M. titillator foraging as well as a survivorship model. These models include a definition of the following components: the relationship between the expected number of D. frontalis in the area foraged by M. titillator [E(SPB¯ 1 )] and the normalized tree bole (obtained by dividing the sample height, S.H., by the infested bole height, I.B.H.); the difference between observed number of D. frontalis in the foraged area (SPB¯ 1 ) and E(SPB¯ 1 )=∆(SPB¯ 1 ) and S.H./I.B.H.; the relationship between the area foraged by M. titillator A¯ 1 and S.H./I.B.H.; the relationship between ∆SPB¯ 1 and A¯ 1 , which is the mortality expression; and the relationship between (SPB¯ 1 )/E(SPB¯ 1 ) and A¯ 1 , which is the survivorship expression. The object of competition between the 2 species is the limited area of inner-bark necessary for development of both species. The form of the competitive process contains elements of both interference and exploitation.

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