1, The rocky habitat communities of Lake Malawi contain a high diversity of
ecologically similar, predominantly herbivorous, cichlid fish species. How so
many species can coexist is still unknown. 2, Adult males of the majority of
these species hold permanent territories which form dense multispecies mosaics
across the shores. 3. The study examined six coexisting species of cichlids
from the rocky habitat where males are known to control access to the algal
food resources within their territorial space. These included four sibling
species of the Pseudotropheus (Tropheops) species complex, which are specialized
epilithic algal herbivores, and two sibling species of the trophically more
generalist P. (Maylandia) species complex which feed upon both epilithic algae
and plankton. 4. The hypotheses that both intraspecific and interspecific
territoriality occur in these communities and that interspecific aggression
initiated by territorial males is preferentially directed at species with the
most similar diets to their own were tested. 5. It was found that males
preferred to exclude conspecific intruders, while they tolerated intruders
with different diets to their own. Also, male P. (Tropheops)
preferentially excluded similar heterospecific dietary specialists, while
male P. (Maylandia) tolerated similar heterospecific dietary generalists.
6. Based on this study, it is proposed that interspecific territoriality
may be reducing competition between species with different diets and
promoting their coexistence, while it may be enhancing competition between
species with the same diet. Furthermore, it suggests that ecological
generalism may be reducing the intensity of interspecific competition,
while specializations for the same resources may be increasing competition.