Dissecting the contributions of dispersal and host properties to the local abundance of a tropical mistletoe

Abstract

Summary 1.The interplay between dispersal and adaptation to local environments ultimately determines the distribution of plant species, but their relative contribution remains little understood. Tropical mistletoes provide the opportunity to dissect these contributions of dispersal and adaptation, because as hemiparasitic plants, they are typically adapted to grow on a handful of species within diverse tropical communities and are non-randomly dispersed by mutualistic frugivorous birds. 2. Here we hypothesized that the primary determinant of the abundance of a tropical mistletoe (Dendropemon caribaeus, Loranthaceae) in Puerto Rico will be the compatibility between the mistletoe and plant species in a community. Alternatively, the mistletoe's abundance could be primarily shaped by other factors such as the availability of potential host plants, or factors that determine how mistletoe seeds are dispersed by avian frugivores. We conducted surveys and experiments to assess the capacity of this mistletoe to grow on trees available in the local community, and measured the monthly phenology and seed dispersal patterns of the mistletoe and other bird-dispersed plants in the community over a period of 4 years. A path model was used to evaluate how the abundance of the mistletoe was shaped by host abundance, fruiting phenology, bird dispersal and compatibilities with host plants. 3. Our analyses show that the compatibility between mistletoe and host tree species, measured by mistletoe survival and growth rate, was the most important factor for mistletoe abundance. The next most important factor was the phenological characteristics of the hosts; this outcome likely arose because frugivory and seed dispersal services for mistletoes and hosts are performed by the same birds. 4. Synthesis. Mistletoes often parasitize only a subset of the suitable plant species that are available in a given community. Our results indicate that such patterns are not only determined by host quality and abundance but also by the phenological patterns of trees that influence the probabilities of mistletoe seeds being deposited on them by shared avian seed dispersers.

Diet complementation as a frequency‐dependent mechanism conferring advantages to rare plants via dispersal

“…By mixing different fruit resources to balance their diets, frugivores promoted rare species overrepresentation in the seed rain. Furthermore, our findings provide a theoretical foundation to empirical studies showing that frugivory can play a central role in diversity maintenance of plant communities where plant–frugivore mutualisms are common (Carballo‐Ortiz, González‐Castro, Yang, dePamphilis, & Carlo, ; Carlo & Morales, ; Herrera, ), and where diet complementation is a component of frugivore foraging (Murphy, ). Results also show that resource provisioning effectiveness (RPE) depends to a great extent on the spatial configuration of fruiting resources, which in turn dictates the energetic costs that frugivores will have to pay to balance their diet.…”

How does avian seed dispersal shape the structure of early successional tropical forests?

“…Non‐random interactions of frugivores with the plant community can also explain the apparent contradiction of the cumulative species richness of seed‐additions being higher for the Bird treatment than the Landscape treatment. Since our Local and Landscape seed‐addition treatments were made in accordance to fruit availability, plant species that dominated seed‐additions between consecutive months tended to be the same dominant species that have long fruiting phenophases (Caraballo‐Ortiz et al, ). On the other hand, rare‐biased dispersal by birds integrated different rare plant species as they became available, leading to more heterogeneous seed‐additions between months (Figure ).…”

“…At the top of each pipe, we installed two perpendicular wooden rods (50 cm long, 0.5 cm in diameter) to serve as perches (Figure ). We verified the effectiveness of these perches in attracting birds by using video cameras to record the activity and behaviour of visitors (see Caraballo‐Ortiz, González‐Castro, Yang, dePamphilis, & Carlo, ). To sample the seed rain under the bird perches, we attached two plastic seed traps (14 cm × 14 cm area) to the pipe 1.5 m from the ground (Figure ).…”

“…Treatments simulated seed dispersal as chance encounters between birds and fruits available in the environment across times, locations and the Local and Landscape spatial scales. Availability of seeds (within fruits) was assessed during the first week of each month by counting the number of ornithochorous fruits that were already ripe or could ripen during that month (Caraballo‐Ortiz et al, ). Availability for seed‐additions in Local treatments was measured by counting ripe fruit on all individuals of each ornithochorous plant species found within a 50‐m radius from each plot each month, then multiplying the fruit counts of each species by the mean number of seeds per fruit of the species.…”

Reproductive ecology of a parasitic plant differs by host species: vector interactions and the maintenance of host races

“…For other mistletoe species that share dispersers with their host species, synchrony between host and parasite fruiting phenology can increase seed dispersal rates for both species (van Ommeren and Whitham 2002;Candia et al 2014). Host fruiting phenology and attractiveness to dispersers can also have a large effect on mistletoe prevalence independent of host-parasite compatibility (Caraballo-Ortiz et al 2017). It should be noted, however, that disperser activity need not be correlated with host or mistletoe fruiting depending on the specifics of dispersers' diets (see Ladley and Kelly 1996 for activity related to host flowers and honeydew producing insects).…”