Territoriality and the Coexistence between the Introduced and the Native Mbuna of the Lake Malaŵi National Park

Paul Makocho1, and Jay Stauffer2

1. Malawi University of Science and Technology, Malawi

2. Penn State University, USA

Abstract: The rock-dwelling cichlids, mbuna, of the Lake Malaŵi National Park are astoundingly rich and diverse, and globally represent the most splendid examples of adaptive radiation. They include introduced mbuna, endemic to other parts of the lake. The elucidation of factors, which have sustained the coexistence of the native and the introduced species for well over 30 years, has been and continues to be a major challenge to contemporary aquatic ecologists. A study was carried out at Thumbi West Island near Mitande Point (S14' 01.444; E034'49.380), to examine the extent to which intra-and interspecific rock-size preference, territoriality and feeding site specifity, combined to promote the coexistence of four native species: Labeotropheus fuelleborni, Melanonchromis auratus,

Pseudotropheus tropheops “intermediate” and Petrotilapia “mumbo blue”, and two introduced species: Metriaclima callinos, and Tropheops sp. “red cheek”.

An underwater substrate configuration of an area of 25 m × 5 m was mapped using underwater semi- transparent A2 graphed tracing films, an A2 graphed plastic board, and two 1m x 1m steel quadrats with the aid of mask and snorkel, and SCUBA. Mapping of territories relied on marking attack points and outermost points of a foraging territorial fish on an A2 underwater semi-transparent sheet corresponding to the mapped substrate configuration.

Males and females of both Pseudotropheus species defend territories, which do not overlap mostly. Territory characteristics exist among the species. Tropheops “intermediate” males and females established territories with dense algal growth; males and females of Tropheops “red cheek” the established territories with little algal growth. There were no distinct feeding sites in the territories of the natives, while the territories of the introduced species had distinct feeding sites. Introduced individuals also established larger territories compared to the native species. The mean territory sizes of 0.40 m²±0.03, n = 72, and 0.17 m²±0.02, n = 32 for the introduced and the natives respectively, were statistically different (t = 5.2, P >.05). Intraspecific territory sizes were not different. For the introduced species, the mean territory sizes of 0.240 m²±0.04, n = 24, and 0.40 m2±0.04, n = 48, for the males and the females respectively, were not statistically different (t = 1.03, P > .05). Similarly, the mean territory sizes of 0.20 m²±0.02, n = 18, and 0.25 m²±0.02, n = 14, for the males and the females respectively, of the native species were also not statistically different (t = 1.9, p > .05).

Tropheops “intermediate” males established territories used for both feeding and mating. Tropheops “intermediate” females established territories, which they used for feeding and brood guarding. Tropehops “red cheek” established territories used for feeding only. Labeotropheus fuelleborni and most of the male M. callinos did not defend territories but established distinct feeding sites. M. auratus and Petrotilapia mumboensis neither defended territories nor established prominent feeding sites.

The distribution and arrangement of mostly non-overlapping territories and feeding sites suggest spatial segregation, which potentially promotes the coexistence of the introduced and the native species at Thumbi West Island.

Key words: coexistence, resource partitioning, interspecific competition, intraspecific competition, conspecifics, consexual, trophic specialization, food-switching