Life‐history divergence facilitates regional coexistence of competing Ficedula flycatchers

Abstract

Abstract. Regional coexistence of ecologically similar species is facilitated when fluctuations in environmental conditions favor different species at different times or places. However, why species with similar ecology should vary in their response to environmental change is unclear. In this study, we explore the role of a life-history divergence in causing changes in relative fitness across environmental conditions experienced by populations of two closely related Ficedula flycatchers on the Baltic island of Ö land, Sweden. We compared patterns of nestling survival between Pied (Ficedula hypoleuca) and Collared (F. albicollis) Flycatchers in relation to two factors known to influence the environment experienced by nestlings: natural variation in their parents' onset of breeding and artificial manipulation of the brood size. Possible differences in the location of the nests (i.e., microhabitat differences) or in habitat use (i.e., feeding patterns) by the adult birds were controlled for by partial crossfostering of young between the two species. We found that nestling mortality was relatively higher among Collared Flycatchers and that this difference increased with later breeding. Mass gain, which predicted survival probability, of nestling Collared Flycatchers did not respond to the seasonal decline in environmental conditions when they were raised in nests with reduced brood size (i.e., where sibling competition was experimentally reduced). This latter result suggests that the smaller clutch size of Collared Flycatchers reflects an adaptive adjustment to their offspring's higher sensitivity to environmental change. We discuss the possibility that the divergence in life-history traits between the two species represents adaptation to different environments experienced during their recent evolutionary history. We conclude that the survival of nestling Collared Flycatchers is more sensitive to harsh environment and that this is likely to limit where and when the more aggressive Collared Flycatchers are able to displace Pied Flycatchers. Our results provide support for models of species coexistence that emphasize the importance of spatial or temporal heterogeneity in relative fitness or life-history divergence. More precisely, our results demonstrate that variation in life-history adaptations may result in changes in relative fitness of species across environments despite their use of similar resources.

Inferring Individual Inbreeding and Demographic History from Segments of Identity by Descent inFicedulaFlycatcher Genome Sequences

“…The time series of estimates of N e suggest a recent and substantial restriction in this population ( Figure 11). These results are consistent with the hypothesis of a recent founding event for the collared flycatchers on the island of Öland (Qvarnström et al 2009). …”

“…Additionally, the tendency of IBDNe to smooth over sudden changes in N e (Browning and Browning 2015) means we cannot precisely pinpoint the timing of the founding event. However, our results suggest that the population was founded no earlier than 60 generations ago (Qvarnström et al 2009). …”

Causes and Consequences of Behavioral Interference between Species

“…However, thinking in terms of population mean fitness is useful for predicting the outcome of species interactions, and there are situations in which behavioral interference could raise the population mean fitness of one of the two species, relative to the alternative of coexisting without behavioral interference. For example, when species overlap in resource use, interspecific territorial aggression might increase the population mean fitness of a dominant species by reducing exploitative competition with a subordinate species [59,60]. Understanding fitness effects at both the population and individual levels is key to predicting the ecological and evolutionary consequences of behavioral interference.…”

“…Modified, with permission, from [18]. deciduous forest in Central Europe is a possible example [58,59]. In other cases, aggressive interference can enable coexistence by causing temporal shifts in habitat use.…”

Variation in Elevation and Sward Height Facilitate Coexistence of Goose Species through Allometric Responses in Wetlands

“…Coexistence of similar species may occur if fluctuations in environmental conditions favor different species at different times or places (Amarasekare and Nisbet 2001). A life-history trade-off is often used to illustrate species coexistence when competition for resources is asymmetric (Skellam 1951;Qvarnstrom et al 2009). For species having a rather similar life-history, resource partitioning and environmental heterogeneity may mediate species coexistence.…”