Seasonal change in the structure of fig-wasp community and its implication for conservation

Abstract

Figs (Moraceae) and their pollinating wasps (Agaonidae) constitute a famous reciprocal mutualism in which figs provide some female flowers for the development of fig wasp offspring while the fig wasps pollinate fig flowers. However, figs also host many non-pollinating wasps which are either parasitoids or resource competitors of pollinators, and bring no benefit for figs and are detrimental to fig' fitness. Our data on Ficus racemosa in Xishuangbanna showed that the numbers of non-pollinators and the mature syconia without pollinator wasps increase in rainy season, especially in the highly fragmented forest. This might be because of the longer developing time of the syconia and thereby longer oviposition time to non-pollinators in the dry season. The galled flower and the viable seed percentages in dry seasons are also larger than in rainy seasons in both primary forest and fragmented forest, and the development of non-pollinators is mainly at the expense of pollinator wasps. Our results showed that there exists a discriminative seasonal impact of non-pollinators and fragmentation effects on population size of fig's pollinators. This implies that fig/fig wasp mutualism is more fragile in dry season, and that the critical population size and breeding units of figs in seasonal area might be larger than previously estimated without considering the seasonal change of pollinator population.

Spatial heterogeneity and host repression in fig-fig wasp mutualism

“…Foundress number per syconium also increased with fruit size (N=93, (Figure 4, also see [29]). The quick closure of osiole will prevent the extra more pollinator wasps from entering the syconium cavities and/or from exiting the syconium cavities after pollinators entering lumen, which will create the intensive interference competition among the foundresses in their egg preposition [16]. The experiment here also showed that in the cold season, the ostiole closure will be much slower than that in the warm season after the foundress entering into the syconium cavities.…”

“…Non-pollinators of gall makers in fig/fig wasp mutualism could independently oviposit in the female flowers of F. racemosa and thereby impede both pollinator and viable seed production [23,25,26,40,59,60]. Gall and seed numbers may be greatly affected by non-pollinator oviposition in highly fragmented forests where non-pollinator density is much higher [16,25]. Our experiments in highly fragmented areas showed that viable seed numbers decline with increasing numbers of wasp offspring when we excluded non-pollinators in January but there was no relationship under natural conditions (Table 1).…”

“…Mean annual precipitation is 1,557 mm with about 80% occurring during the rainy season [26]. The mean annual temperature is 21°C, but the temperature between November to February is much lower than in other months [16,26]. [11,12].…”

“…However, many Ficus species receive multiple foundresses, and foundress numbers can vary dramatically between species [15,21]. Density dependent interference competition between the foundresses together with high temperature may be responsible for per capita reductions in the numbers of offspring in figs entered by increasing numbers of females [16,22]. However, this hypothesis does not efficiently explain why direct conflict could be observed in both warm and cold seasons occasionally [22], and it also does not make clear on if the interference competition and high temperature could exclusively explain the fig-fig wasp mutualism stability.…”

Varying coefficient analysis for indeterminate species interactions with non-parametric estimation, exemplifying with a fig-fig wasp system

“…Species interactions can also be conspecific density-dependent, such as through competition, or vary with the population density of other species [16,34,35]. This variation can cause large changes in the interaction between species [16].…”