Is Markhamia lutea’s abundance determined by animal foraging?

Abstract

Understanding the determinants of tropical forest tree richness and spatial distribution is a central goal of forest ecology; however, the role of herbivorous mammals has received little attention. Here we explore the potential for red colobus monkeys (Procolobus rufomitratus) to influence the abundance of Markhamia lutea trees in a tropical forest by feeding extensively on the tree’s flowers, such that this tree population is not able to regularly set fruit. Using 14 years of data from Kibale National Park, Uganda, we quantify M. lutea flower and fruit production. Similarly, using 21 years of data, we quantify temporal changes in the abundance of stems in size classes from 1 m tall and above. Our analyses demonstrate that M. lutea is rarely able to produce fruit and that this corresponds to a general decline in its abundance across all size classes. Moreover, using 7 years of feeding records, we demonstrate that red colobus feed on M. lutea, consuming large amounts of leaf and flower buds whenever they were available, suggesting that this behavior limits fruit production. Therefore, we suggest that red colobus are presently important for structuring the distribution and abundance of M. lutea in Kibale. This dynamic raises the intriguing question of how a large M. lutea population was able to originally establish. There is no evidence of a change in red colobus population size; however, if this old-growth forest is in a non-equilibrium state, M. lutea may have become established when red colobus ate a different diet.

Solar radiation and ENSO predict fruiting phenology patterns in a 15‐year record from Kibale National Park, Uganda

“…Similarly, folivores often feed heavily on flowers, effectively eliminating pollination and stopping fruit set. Within Kibale, red colobus monkeys (Piliocolobus tephrosceles) feed so heavily on the flowers of Markhamia lutea that trees in the forest have not set fruit in decades, but trees in neighboring forest patches, without the colobus monkeys, fruit annually (Chapman et al 2013b). Similarly, folivores can eat the unripe fruit of some species dramatically affecting fruiting (DaSilva 1992).…”

Towards effective monitoring of tropical phenology: maximizing returns and reducing uncertainty in long‐term studies

“…For instance, more regular flowering than fruiting could arise because trees may abort their reproductive efforts after poor pollination or unfavorable weather conditions, or because of widespread removal of flowers by florivores ( e.g ., red colobus monkeys, Procolobus rufomitratus, in Uganda; Chapman et al . ).…”

Seasonal importance of flowers to Costa Rican capuchins (Cebus capucinus imitator): Implications for plant and primate

“…While flowers constitute a small proportion of the annual capuchin diet, we show that they play an important role in the seasonal diet at our field site. Flower foraging also has the potential for broad community effects by inhibiting or promoting the reproduction of some plant species, ultimately shaping their distribution and abundance (Chapman et al, ; McCall & Irwin, ). The downstream impacts of capuchin flower foraging on fruit set would be an important question for future research.…”

“…In turn, angiosperms are highly dependent on animals for their reproductive success (Vázquez et al, ). Primates often serve in this role, improving or reducing plant reproductive success either directly through seed dispersal and fruit predation (Chapman, ; Valenta & Fedigan, ) or indirectly via folivory (Chapman et al, ; Hendrix, ; Oppenheimer & Lang, ). Although not widely studied, primates and other plant foraging animals may also directly affect plant reproductive success via flower foraging (McCall & Irwin, ; Heymann, ).…”