Long term patterns of temporal mate restriction and reproductive structure in trees from a tropical peat swamp forest.

Background/Question/Methods

In many populations of plants and animals not all individuals reproduce at the same time. This results in restricted mating opportunities, with implications for population vital rates and genetics. The study of reproductive asynchrony and its effects has primarily focused on iteroparous organisms including insects, salmon, or biennial plants. To study mate restriction and potential consequences for long-lived semelparous organisms, such as tropical trees, longer term data is needed. Here, we use a 17-year time series consisting of monthly phenological observations to ask 1) what proportion of neighboring trees an individual tree can outcross with over time, 2) whether certain individuals tend to flower together repeatedly, and 3) whether individuals differ in the overall synchronicity of their flowering. Data were collected from study plots in a tropical peat-swamp forest at the Tuanan Research Station, Central Kalimantan, Indonesia. First, we evaluate how individual trees accumulate co-flowering partners over time. Second, to evaluate potential for assortative mating, we compare the observed distributions of co-flowering to permutational nulls. Third, we calculate the proportion of the conspecific population in flower each time a given individual flowers and use permutational ANOVA to evaluate whether mean synchronicity differs between individuals.

Results/Conclusions

We analyzed temporal flowering patterns for populations of 15 abundant annually or sub-annually flowering species with perfect (bisexual) flowers. For all but 3 species, individuals had co-flowered with most of their neighbors within 17 years and were projected to co-flower with all neighbors within typical tree lifespans (Q1). This was true even for some species in which individuals co-flowered with only a few neighbors in each flowering event. In all species, we observed only a weak and statistically non-significant tendency for some pairs of trees to co-flower more often than others (Q2). In other words, we did not find that individuals differed in the identity of their co-flowering partners. Generally, individual timing of flowering did not follow patterns that would lead to life-time restriction of out-crossing partners, or that could lead to temporal genetic structure in these populations. For 5 of the 15 species, we found significant differences in mean synchronicity between individuals: that is, individual trees differed significantly in their mean quantity of co-flowering partners (Q3). For species with large differences in synchronicity between individuals, reproductive asynchrony may contribute to increased variation among individuals in life-time reproductive output, which would in turn reduce effective population sizes.