Directness and tempo of avian seed dispersal increases emergence of wild chiltepins in desert grasslands

Abstract

Summary1. Seed dispersal is thought to be unpredictable and outside a plant's control. But directed seed dispersal by mutualistic birds can increase probabilities of germination and survival by the non-random deposition of seeds in suitable microhabitats. 2. In the Sonoran Desert grasslands of southern Arizona (USA), bird-dispersed wild chiltepin peppers (Capscium annuum var. glabriusculum) grow in non-random association under bird-dispersed nurse trees and shrubs that serve as perches. We tested the hypothesis that the pattern is maintained by directional avian seed-dispersal patterns. Alternatively, post-dispersal processes, such as differential seed predation and seedling mortality, could create the associations. 3. For 3 years, we sampled the bird-generated seed rain under desert trees in four chiltepin subpopulations, comparing seed dispersal into microhabitats of fleshy-fruited trees and non-fleshy-fruited trees. Celtis pallida (fleshy-fruited) and Prosopis vellutina (non-fleshy-fruited) trees accounted for > 90% of the cover available for chiltepin recruitment. We tracked seedling emergence and survival in the two microhabitats and conducted a controlled seed-addition experiment to measure the effects of microhabitat, seed-addition density and temporal seed deposition on chiltepin emergence, growth and survival. 4. Approximately twice as many bird-dispersed seeds arrived at fleshy-fruited microhabitats compared with non-fleshy microhabitats. The numbers of seeds arriving and the number of seedlings emerging in microhabitats the following year were positively correlated. Survival of naturally emerged seedlings was similar at both microhabitats, but the seed-addition experiment revealed that more seeds are able to emerge under the denser foliage of fleshy-fruited microhabitats. The experiment also shows a significant effect of temporal deposition: when seeds were added gradually in a microhabitat (emulating repeated avian seed deposition under perches) instead of all at once, seedling emergence increased twofold on average. 5. Synthesis: Birds dispersed disproportionally high quantities of chiltepin seeds into favourable recruitment microhabitats, showing a case of directed dispersal. Birds also increase seedling emergence through the temporal deposition of seeds under fleshy-fruited trees, most likely as a result of reducing the odds of seed predation. A coupling between directed seed dispersal with classic facilitative plant-plant interactions leads to the formation of pattern and self-organization in a plant community.

Generalist birds promote tropical forest regeneration and increase plant diversity via rare‐biased seed dispersal

“…Post-dispersal seed predation and density-dependent seedling mortality can be very high under bird perching sites receiving a copious seed rain (Holl 1998, Spiegel and Nathan 2011, Carlo and Tewksbury 2014 and it can slow down plant establishment (Reid and Holl 2013). Post-dispersal seed predation and density-dependent seedling mortality can be very high under bird perching sites receiving a copious seed rain (Holl 1998, Spiegel and Nathan 2011, Carlo and Tewksbury 2014 and it can slow down plant establishment (Reid and Holl 2013).…”

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…Indeed, in a desert grassland and a temperate heterogeneous system seed deposition was higher under fruiting canopies Carlo and Tewksbury, 2014). Carlo et al (2013) found that long distance dispersal events (distances of 150-700 m) were much more likely to occur under fruiting canopies than non-fruiting.…”

“…Long distance dispersal events are important for plant community stability by maintaining gene flow. Additionally, Carlo and Tewksbury (2014) found that chiltepin pepper (Capscium annuum var. glabriusculum) seeds that were artificially added and arrived there via bird dispersal under dense fruiting shrubs exhibited increased recruitment, leading them to conclude that dispersal of these peppers was directed to favorable microhabitats.…”

Interspecific associations in seed arrival and seedling recruitment in a Neotropical forest

“…, Garcia et al. , Carlo and Tewksbury ). Negative and positive outcomes dependent on associations with other species have been termed associational susceptibility and resistance, respectively, and are well documented for plant–herbivore interactions (reviewed by Barbosa et al.…”