Temporal and spatial differentiation in microhabitat use: Implications for reproductive isolation and ecological niche specification

Abstract

Niche differentiation enables ecologically similar species to coexist by lessening competition over food and/or shelters and may be critical for reproductive isolation between closely related species in close proximity. Because no extra traits need to evolve, spatial and temporal differentiation may readily take place to complement other isolating mechanisms. Two closely related treefrog species occur together in Korea: the endangered Hyla suweonensis and the widespread Hyla japonica. Advertisement calls are differentiated, but it is unclear whether call difference is sufficient for reproductive isolation. We tracked individuals of both species to study fine-scale differentiation in microhabitat use in the diel cycle of the breeding season using a harmonic direction finder. tracking male movement patterns of both species revealed spatial and temporal differentiation in microhabitat use for calling and resting during the breeding season. Males of both H. suweonensis and H. japonica occurred in all 5 microhabitats identified in this study: rice paddy, ground, buried, grass and bush. Both treefrog species showed general similarities in calling from rice paddies and resting in grass and bush. However, H. suweonensis moved into rice paddies and produced advertisement calls 3 h earlier than H. japonica. These differences likely minimize contact between the species and provide an additional isolating mechanism. In addition, the activity of H. suweonensis may be contributing to the decline of this species, as resting in grass would increase dangers from predatory birds and habitat disturbance.

Introduced bullfrogs are associated with increased Batrachochytrium dendrobatidis prevalence and reduced occurrence of Korean treefrogs

“…suweonensis produce advertisement calls at the center of flooded rice paddies, whereas male D . japonicus call from the banks of rice paddies, outside of water [54]. Such a niche segregation between the two species results in D .…”

“…Dryophytes suweonensis is active at higher temperatures than D . japonicus [54], but it is not known whether these two species differ in basking behavior. Thus, despite D .…”

Asymmetric competition over calling sites in two closely related treefrog species

“…A tracking experiment showed that both treefrog species spent their days on rice paddy banks resting, hiding, and feeding28. Unlike natural ditches, concrete ditches typically remain dry, which limits grass growth.…”

“…In a lone semi-natural habitat for H. suweonensis , males of both species were calling at the edge of the wetland20. However, male H. suweonensis generally call in the middle of rice paddies and H. japonica males call at the edge of rice paddies22. The levee of rice paddies are typically composed of soils with grasses, which provide solid sites for calling treefrog males.…”

Peer Review #2 of "Impact of land reclamation and agricultural water regime on the distribution and conservation status of the endangered Dryophytes suweonensis (v0.1)"

“…Along this central ditch, and thus along the longest and straightest line available, usually runs a cemented lane, typically following the centre of the valley. In this study, ricepaddy complexes were considered spatially independent if further than 200 m apart, the maximum daily dispersion distance for the species (Borzée et al 2016a), or separated by landscape barriers impermeable to treefrogs (Roh et al 2014).…”