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Shape Divergence Associated with Size Convergence in Sympatric East African Jackals
Author(s) -
Van Valkenburgh Blaire,
Wayne Robert K.
Publication year - 1994
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1939618
Subject(s) - character displacement , jackal , sympatric speciation , sympatry , ecology , sexual dimorphism , biology , allopatric speciation , crania , zoology , population , demography , anatomy , sociology
The geographic ranges of three extant species of medium—sized canid, the sidestriped (Canis adustus), the golden (C. aureus), and the blackbacked (C. mesomelas) jackal, overlap only in East Africa. Elsewhere each species exists alone or in sympatry with one other jackal species. The fossil record suggests that the golden jackal evolved outside of Africa and joined the other two species in East Africa within the last 500 000 yr. Previous research showed that unlike other sympatric canids, all three jackal species in East Africa are extremely similar in size and overall morphology and thus exhibit no obvious evidence of ecological character displacement. Moreover, the three species do not form a monophyletic group, are distantly related, and thus may have had ample time to diverge morphologically. Here, we explore in further detail the possibility of character displacement in the three species by assessing variation in 62 measures of the skull and teeth for populations of all three species throughout their ranges. The expanded measurement and population sample allows us to explore four possible manifestations of character displacement: (1) divergence in size, (2) divergence in shape, (3) reduced morphological variability, and (4) reduced sexual dimorphism. There is no evidence of size divergence among jackals in East Africa; by contrast the three species appear to converge on a similar size. However, divergence in shape is apparent. The recent insinuation of golden jackals into the East African fauna has resulted in character divergence and probable niche compression of blackbacked jackals as evidenced by adaptations for increased carnivory, reduced sexual dimorphism, and reduced variability. The response has been asymmetric as the golden and sidestriped jackals have not diverged functionally or shown niche compression. The pattern of character displacement is likely a function of starting conditions at the time the three became sympatric. The golden jackal exhibits dietary adaptations intermediate to those of the other two species but more similar to those of blackbacked jackal. Thus character displacement was more likely to occur in goldens and blackbacks. Selection for increased carnivory in the blackbacked jackal might have been favored because of the abundance of vertebrate prey in the East African plains. The success of the golden jackal as an insinuator into East Africa suggests that the carnivore guild might not be saturated.