Resource partitioning or reproductive isolation: the ecological role of body size differences among closely related species in sympatry

Abstract

Summary1. Body size differences among coexisting related species are common, but the actual effect of these differences in mitigating interspecific interactions, such as resource competition and reproductive interference, is poorly understood. 2. Local assemblages of the ground beetle genus Carabus (subgenus Ohomopterus) typically consist of two or more species of varying sizes. Through foraging and mating experiments using four Ohomopterus species in parapatry and sympatry, we examined whether interspecific body size differences are effective in partitioning food resources or reducing reproductive interference. 3. Because larval Ohomopterus feed exclusively on earthworms, body size differences may be related to partitioning earthworms of different sizes. However, larvae did not exhibit differences in selectivity or attack success on earthworms of different sizes based on larval body size, indicating little possibility of partitioning food by body size. 4. In contrast, interspecific mating behaviours, such as mate recognition, mounting, and copulation, were hindered when body size differences were large; copulation was frequently accomplished between parapatric species with smaller body size differences. 5. These results suggest that body size differences between species effectively reduce reproductive interference, rather than resource competition. Although body size differences in coexisting closely related species have been considered to function in resource partitioning, they may function primarily in reproductive isolation and thereby facilitate coexistence of species.

Reproductive interference: ecological and evolutionary consequences of interspecific promiscuity

“…If an interspecific difference in a specific trait prevents the occurrence of reproductive interference, that trait difference may persist in coexisting species in nature as a result of ecological or evolutionary process (e.g., Okuzaki et al 2010;Eaton et al 2012). On the one hand, species with similar traits may exclude each other, and species may be sorted in the way that local assemblage consists of species with persistent trait difference.…”

“…On the one hand, species with similar traits may exclude each other, and species may be sorted in the way that local assemblage consists of species with persistent trait difference. For example, if a small body size difference results in costly interspecific copulation between two closely related species, species with similar body sizes may exclude each other, resulting in a species assemblage with a persistent body size difference (Okuzaki et al 2010). On the other hand, if reproductively interacting species coexist for sufficiently long time without extinction of either species, adaptive evolution may reduce the cost of reproductive interference through a mechanism such as reproductive character displacement in mate recognition traits (e.g., Lemmon 2009;Bargielowski et al 2013;Okamoto and Grether 2013).…”

“…Note that the listed consequences are not mutually exclusive. For example, species may be sorted along a trait axis (e.g., body size) in a local community, but members of the local community may also be parapatric to a member of an adjacent local community (Okuzaki et al 2010) Popul Ecol (2015) 57:253-260 257 food for offspring but also the mating site, reproductive interference by males of another species on a suitable host may drive ovipositing females to seek other host species that are suboptimal for offspring growth. The final two contributions are empirical study reports.…”

Assembly rules for ground beetle communities: What determines community structure, environmental factors or competition?

“…Competition is important in laboratory studies (e.g., Currie et al, 1996). There are studies of the role of competition in speciation but for a few species in nature (Sota et al, 2000;Okuzaki et al, 2010). There are few if any studies on the role of competition in structuring ground beetle communities along environmental gradients, even though such studies are crucial for the understanding the assembly of beetle communities.…”

Ecological differentiation and habitat unsuitability maintaining a ground beetle hybrid zone

“…These results suggest that endogenous selection via reproductive interference facilitated competitive exclusion (Okuzaki et al. 2010). Quantification of reproductive isolation via ecological differentiation (e.g., Ramsey et al.…”