Phenological specialisation of two ant‐dispersed sedges in relation to requirements for qualitative and quantitative dispersal effectiveness

Abstract

Synchronisation of fruiting phenology with disperser activities is an important component of plant adaptation to seed dispersal mutualisms. Although most previous studies have exclusively evaluated the effects of fruiting phenology on seed removal rate, seed dispersal effectiveness is determined by both the number of dispersed seeds (quantitative effectiveness) and the probability of a dispersed seed becomes an adults (qualitative effectiveness). Therefore, the adaptive significance of fruiting phenology should be assessed for both components of dispersal effectiveness. This study investigates the adaptive significance of fruiting phenology for two ant‐dispersed sedges, Carex lanceolata and C. tristachya. Because C. lanceolata is known to require a longer seed dispersal distance than C. tristachya, we hypothesized that C. lanceolata produces seeds when high qualitative dispersal effectiveness can be achieved, while C. tristachya bears seeds when seed disperser ants are abundant to give priority to quantitative dispersal effectiveness. Field observations of ant activity around the sedges revealed that the relative abundance of ant species with the longest seed dispersal distance, Formica japonica, was higher during the fruiting period of C. lanceolata than in that of C. tristachya, which is consistent with the requirement of C. lanceolata to achieve high qualitative effectiveness. In addition, our fruiting manipulation experiment revealed that C. tristachya fruits when the overall seed removal rate is high, resulting in high quantitative effectiveness. Overall, our results support the idea that variations in both qualitative and quantitative dispersal effectiveness should be considered to understand the adaptive significance of fruiting phenology in animal‐dispersed plants.

Extension of the primary dispersal distance through peduncle laying and elongation promotes myrmecochory in Japanese sedges

“…Interestingly, relative primary dispersal distances were greatest in the two late fruiting sedges with small elaiosomes ( C. tristachya and C. pocilliformis ). As late fruiting and small elaiosomes both enhance diaspore removal by short distance ants (Tanaka & Tokuda, 2016, 2017, 2020), the role of peduncle laying and elongation in extending the dispersal distance of short distance ants might be more important in the two late fruiting sedges than in the two early fruiting sedges ( C. mitrata var. mitrata and C. lanceolata ).…”

“…mitrata (KT, unpublished data) and C. pocilliformis (Nakanishi, 1988). The four sedge species investigated here exhibit interspecific differences in elaiosome size and fruiting phenology, both of which affect the ratio of ant species with long or short diaspore dispersal distances (Tanaka & Tokuda, 2016, 2017). Of the four sedge species, C. lanceolata has trait combinations (large elaiosomes, early fruiting) favoring diaspore removal by F. japonica , a large ant with the greatest diaspore dispersal distance among the sympatric ants (Tanaka & Tokuda, 2016, 2017).…”

“…The four sedge species investigated here exhibit interspecific differences in elaiosome size and fruiting phenology, both of which affect the ratio of ant species with long or short diaspore dispersal distances (Tanaka & Tokuda, 2016, 2017). Of the four sedge species, C. lanceolata has trait combinations (large elaiosomes, early fruiting) favoring diaspore removal by F. japonica , a large ant with the greatest diaspore dispersal distance among the sympatric ants (Tanaka & Tokuda, 2016, 2017). In contrast, C. tristachya exhibits the latest fruiting phenology and small elaiosomes, which favor diaspore removal by smaller ant species with shorter dispersal distances (Tanaka & Tokuda, 2016, 2017).…”

“…Of the four sedge species, C. lanceolata has trait combinations (large elaiosomes, early fruiting) favoring diaspore removal by F. japonica , a large ant with the greatest diaspore dispersal distance among the sympatric ants (Tanaka & Tokuda, 2016, 2017). In contrast, C. tristachya exhibits the latest fruiting phenology and small elaiosomes, which favor diaspore removal by smaller ant species with shorter dispersal distances (Tanaka & Tokuda, 2016, 2017). The phenology and elaiosome size of C. pocilliformis are similar to those of C. tristachya , indicating a similar dispersal strategy to that of the latter sedge.…”

“…In addition, both the experimental manipulation and observation of dispersal traits are easier for myrmecochory than other biotic dispersal modes because of their small stature (Leal et al, 2015). The dispersal functions of various plant traits have been examined in myrmecochores, including the size of diaspores and elaiosomes (Hughes & Westoby, 1992a; Leal et al, 2014; Mark & Olesen, 1996; Prokop et al, 2022; Tanaka & Tokuda, 2020), chemical composition of elaiosomes (Gammans et al, 2006; Miller et al, 2020; Pfeiffer et al, 2010), timing of diaspore release (Boulay et al, 2007; Guitián & Garrido, 2006; Oberrath & Böhning‐Gaese, 2002; Ruhren & Dudash, 1996; Tanaka & Tokuda, 2017), and degree of diaspore clumping (Gorb & Gorb, 2000; Hughes & Westoby, 1992a; Ohkawara et al, 1996; Ohkawara & Higashi, 1994).…”