DENSITY AND DISTANCE-TO-ADULT EFFECTS OF A CANKER DISEASE OF TREES INA MOIST TROPICAL FOREST

We compared the spatial distribution of stem cankers on the canopy tre e Ocotea whitei (Lauraceae) in a 20-ha plot on Barro Colorado Island, Panama, with spatial and temporal patterns of mortality in this host o ver the previous decade. The cankers occur both on adult and juvenile individuals, although juveniles are much more likely the adults to sho w symptoms. Disease incidence is host-density dependent, and both the presence of the disease and host mortality are more likely close to th an far from a conspecific adult, which resulted in a net spatial shift of the juvenile population away from conspecific adults through time. Disease incidence is lower than expected among juveniles of 0. whitei growing near to adults of the non-susceptible canopy tree Beilschmied ia pendula. The coincidence of spatial patterns of canker incidence an d host mortality suggest a role for the disease in regulating host spa tial distribution, in agreement with predictions of the Janzen-Connell hypothesis.