Body size and host range co‐determine the altitudinal distribution of Neotropical tephritid flies

Abstract

ABSTRACTAim We addressed the following questions: (1) Does tephritid body size tend to increase in species found at higher elevations, as predicted by Bergmann's rule? (2) Do tephritids conform to Rapoport's rule, so that species found at higher elevations tend to have broader altitudinal ranges? (3) More generally, how do body size and host range jointly affect the patterns of altitudinal distribution among Neotropical tephritid flies?Location The Mantiqueira mountain range, south‐eastern Brazil, at sites ranging from c. 700 to 2500 m a.s.l.Methods At each site we collected flower heads of all Asteraceae species to rear out endophagous immatures (from January to June in 1998 and 1999). We used structural equation models (SEM) to evaluate jointly the relationships between body size, host range and altitudinal distribution (range and mid‐point).Results Neotropical tephritid body size showed a negative relationship with altitudinal distribution. SE modelling showed no significant direct effect of body size on altitudinal range; however, it had significant indirect negative effects through host range and altitudinal mid‐point. The SE model was a good predictor of observed correlations and accounted for 84% of the variation in tephritid altitudinal range.Main conclusions The altitudinal range of flower‐head‐feeding tephritids is related to host range and is indirectly affected by body size via host range and altitudinal mid‐point. As predicted by Rapoport's rule, tephritids that occur at higher elevations also present wider altitudinal ranges. Bergmann's rule does not apply to Neotropical tephritids along a tropical elevational gradient, but rather its converse was found. Body size may determine host range by imposing a restriction upon large individuals using small flower heads. Host species turnover along the altitudinal gradient may be the main factor explaining the strong relationship between host range and insect elevational distribution.