Overlap, Similarity, and Competition Coefficients

Abstract

Several problems arise if niche overlaps are equated with species similarities or interspecific competition coefficients. Niche overlaps based on food types in the diet rely on proportional utilization rates of the different food types. But because proportional utilizations reflect consumer—environment interactions, measures of similarity based on such proportions may reflect similarities between environments rather than similarities between species pairs. Competition coefficients, as derived by MacArthur, weight renewable resources on the basis of their productivity–not their relative abundance. Use of proportional utilization rates intrinsically incorporates relative resource abundance and ignores differences in resource productivity. Thus, equating overlaps based on proportional utilizations with competition coefficients will overestimate the contribution of abundant resources, which will be actually less limiting if they are very productive. These problems are illustrated with the MacArthur—Levin's measure of niche overlap, but the same problems will arise with other measures of overlap. On the other hand, measures of species' similarities which are independent of resource abundance may reflect evolutionary divergence of consumers' resource utilization patterns due to past competitive pressures.

Ecological segregation of bark beetle (Coleoptera, Curculionidae, Scolytinae) infested Scots pine

“…In addition, other researchers (Glasser and Price 1988) observed an increase in niche overlap in when resources were nearly unlimited resources for, inter alia, T. piniperda (Amezaga and Rodrı´guez 1998). This may indicate a low degree of competitive interaction for living space among individuals of the coexisting species (Colvell and Futuyma 1971;Ratchke 1976;Lawlor 1980). The model developed by Price (1997) used for the description of tree infestation patterns shows a positive correlation between the body size of a beetle with the thickness of the phloem and area of the exploited resources.…”

Living together, sometimes feeding in a similar way: the case of the syntopic hylid frogs Hypsiboas raniceps and Scinax acuminatus (Anura: Hylidae) in the Pantanal of Miranda, Mato Grosso do Sul State, Brazil

“…Therefore, a clear understanding of the relationship on niche overlap, similarity and competition among species is necessary to answer questions on community structure (Lawlor, 1980). …”

Reparto de recursos de los gremios de lagartijas en el cañón de Chínipas, Chihuahua, México

“…De manera tradicional para su estudio, el reparto de recursos, se divide en tres categorías dimensionales, el hábitat, el alimento y el tiempo (Schoener 1968;Pianka 1969Pianka , 1973Pianka , 1975, mismas que pueden subdividirse en macrohábitat, microhábitat, tipo y tamaño de alimento y tiempo de actividad estacional y diaria (Schoener 1974). En los estudios de las interacciones de especies y de la estructura de los ensambles es útil cuantificar el grado de traslape entre pares de especies que se presentan al considerar diversos recursos (Hurlbert 1978;Lawlor 1980) así como el grado de especialización. Es por esto que su principal propósito es analizar los límites que la competencia interespecífica impone en cuanto al número de especies que de manera estable pueden coexistir (Pianka 1974;Schoener 1974).…”

“…Es por esto que su principal propósito es analizar los límites que la competencia interespecífica impone en cuanto al número de especies que de manera estable pueden coexistir (Pianka 1974;Schoener 1974). Sin embargo, debe tomarse en cuenta que la medición y la interpretación del traslape de nicho entre especies consumidoras del mismo recurso depende de lo que se está comparando entre ellas; por ejemplo, la morfología, el uso de cierto microhábitat, el tiempo u horario de forrajeo, el comportamiento de alimentación y los recursos consumidos (Lawlor 1980). La mayoría de estos estudios únicamente documentan las diferencias pero no analizan los mecanismos que las causan, ya que de manera conjunta o por medio de un sólo estudio ambas metas son difíciles de alcanzar (Toft 1985).…”