Insect Oak Defoliators Partition Seasonal Time on a Mediterranean Mountain

The insect chewers of oak foliage were studied on a Mediterranean mountain where deciduous oak species coexist with evergreen oak members of vegetation. We found 58 insect species (mainly Lepidoptera) in 20 families. These insects chewed the leaves of 8 Quercus species. The overlap in time and in feeding niche of the insects was examined by the: (a) Poole-Rathcke method, which tests phenological overlap and (b) Petraitis method. The main findings were: 1. The entire assemblage partitioned time in a regular way (Dr=4.16, P < 10-3). 2. It was found that insect families partition seasonal time in a random way. 3. Insect species formed 6 major feeding groups on the basis of the Quercus species exploited as feeding substrate, and individually these species are randomly distributed within the period of a year. 4. On the other hand the insects were found to share time in a variety of ways, which indicates that the overlap in feeding resources is compensated either by regular or random partitioning of time. 5. The hypothesis of complete general overlap is rejected for the different groups of feeding specialization and zoogeographical categories. 6. In a temporal sense only holarctic species partition time in a non-random way. 7. The specific niche overlap among insects is highly asymmetrical. 8. Food specialists were found to have random phenologies unlike the other specialization groups. In addition they have smaller dispersion ratio than the other specialization groups. Presumably this is used by small groups to relax high overlap. The overall conclusion is that in the oak foliage insect feeding guild the spatial overlap is compensated by a regular or random time partitioning. This work shows that the details of time partitioning are affected by the geographical distribution and feeding specialization of insect members.