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Ecological and Competitive Relations Among Three Species of Frogs (Genus Rana)
Author(s) -
Inger Robert F.,
Greenberg Bernard
Publication year - 1966
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1934261
Subject(s) - interspecific competition , ecology , biology , competition (biology) , ecological niche , niche , fauna , population , extinction (optical mineralogy) , streams , ecological release , intraspecific competition , habitat , paleontology , computer network , demography , sociology , computer science
Interspecific competition is often advanced as an explanation for replacement of species by ecological counterparts. Where environments are stable, as in controlled laboratory experiments, interspecific competition usually leads to the extinction of one species. In a complex natural environment, fluctuations in physical and biotic factors may long delay competitive exclusion. The existence of three related species of frogs (genus Rama) confined to stream in tropical rain forest provided an opportunity to manipulate natural populations and thus to study the relation between overlap in niches and interspecific competition. A rain forest area was chosen because it lacks significant seasonal variation in rainfall, temperature, and photo—period and consequently prevents seasonal specialization of the fauna. These three species, R. blythi, R. ibanorum, and R. macrodon, proved to be very similar in habits. Rana blythi is larger than the other two and usually was found farther from the stream bed. Rana macrodon reaches sexual maturity faster than the others and R. ibanorum lays fewer eggs. Nonetheless it is clear that their niches overlap extensively. Populations of these frogs were studied on surveyed portions of three streams by mark and release techniques. Populations of R. blythi on one stream (Sungei Ensurai) and R. ibanorum on another (Sungei Sekentut) were initially much smaller than the respective populations on the other streams. Following removal of R. blythi from Sungei Sekentut and of R. ibanorum from Sungei Ensurai, leaving the populations on Sungei Serbong as controls, R. blythi on Sungei Ensurai appeared almost to double in numbers and to reach the population levels originally found on the other streams. Population estimates of R. ibanourm on Sungei Sekentut fluctuated, being larger at midyear; statistical support for this variation is weak. Rana macrodon seemed to quadruple its numbers on Sunge Sekentut. There is evidence that macrodon is in the process of invading this part of Borneo and may be doing so at the expense of R. ibanorum. Maximum population levels for the blythi and ibanorum may be fixed by intraspecific competition, which in turn may be responsible for maintaining the coexistence of these related species.