Early threads

Spiders are generalist predators with overlapping diets who are hungry most of the time. They ought to compete with each other for food. It is not surprising that arachnologists have invoked interspecific competition to explain patterns in spider communities. The original impetus was neither experimental evidence of food limitation nor general arguments, such as that advanced by Hairston, Smith & Slobodkin (1960) that terrestrial carnivores are food limited and therefore should compete. Instead, motivation sprung from the fascination with interspecific competition that has permeated ecology since Charles Darwin. An early, extensive statement of the competitionist view of spider communities occurs in the review by Erwin Tretzel (1955).

Tretzel used the term ‘intragenerische Isolation’ to describe differences in spatial and temporal distribution observed for congeneric species; the term could be translated broadly as ‘niche partitioning within genera.’ Espousing a world view held by other ecologists of his time, Tretzel argued that interspecific competition has been a major cause of ecological isolation between closely related spiders, and that evolved differences in seasonal timing of reproduction, horizontal habitat utilization and daily activity patterns are the most common adaptations permitting the coexistence of competing spider species (Fig. 3.1). Vertical stratification in the same area is not as effective, he reasons, because of the lack of prey specialization shown by most spiders. Before presenting numerous examples of spatial and temporal segregation in spiders, Tretzel traces the history of the concept.