In our latest Insight, Dr Aarón González Castro (Spanish National Research Council) talks about a recent paper he has co-authored with Dr Suann Yang (State University of New York at Geneseo) and Dr Tomás A. Carlo (Pennsylvania State University) on “How does avian seed dispersal shape the structure of early successional tropical forests?”, his research and the best (and worst!) things about being an ecologist.

En nuestro último “Insight”, Aarón González Castro (Consejo Superior de Investigaciones Científicas) nos habla sobre un artículo que ha publicado recientemente junto a sus colegas, la Dra. Suann Yang (Universidad Estatal de Nueva York en Geneseo) y el Dr. Tomás A. Carlo (Universidad Estatal de Pensilvania) titulado: “How does avian seed dispersal shape the structure of early successional tropical forests?”. Resumen en español.

About the research

What’s your paper about?

Grey kingbird eating fruit of Cupania americana
Grey kingbird eating fruit of Cupania americana

This paper is about how fruit-eating birds can leave a characteristic ‘signature’ on regenerating tropical plant communities. More specifically, it’s about how species composition and abundance of new plant communities can differ significantly from what would be expected if birds select fruits (and so disperse their seeds) randomly, and how these non-random choices can help plant species coexistence (i.e., biodiversity maintenance).

What’s the background behind your paper?

Study Area
Study Area

Since the 80s, many papers have shown the importance of avian frugivores as seed dispersal agents for fleshy-fruited plants in different biomes worldwide. Birds provide seed dispersal services that maintain many plant populations, influencing the composition of regenerating forests. But until now, ecologists knew little about the degree to which the composition of regenerating forests is influenced by the fruit-choices of birds, which is important for understanding how much birds shape forests in non-random ways. Since Janzen and Connell’s publications in the 70s, antagonistic interactions between plants and their natural enemies (pathogens, herbivores or seed predators) are among the most accepted processes regulating the coexistence of plant species.

In our paper (along with others by Dr Carlo), we propose a plausible way for mutualistic interactions to mediate plant species coexistence, as bird seed dispersers not only boosted the presence of some already abundant plant species, but also promoted the presence of rare plant species in emergent communities.

Who should read your paper (and why)?

Everybody, of course! This paper raises questions that could be interesting for ecologists interested in mechanisms of plant species coexistence. Avian dispersers are important for plant species throughout different biomes, but other animals can act as seed dispersers everywhere else (mammals, lizards, ants, etc.), so the approach used for this paper could be applied to understanding the importance of mutualistic interactions for restoration and regeneration of other forest habitats.

It also contains information that could help policy-makers and environmental managers interested in forest restoration. Lastly, if you are not an ecologist, this paper could be useful more generally; it could even help you to capture sleep during sleepless nights!

What makes your paper different from previous work on avian seed dispersal?

Experimental plotOne of the most innovative aspects of our work was the experimental design (conceived by Dr Carlo and Dr. Yang), a field experiment where we could compare the actual seed dispersal patterns by birds, and the resulting communities of emerging plants, to those developed from experimental seed-additions that emulated birds feeding at random on the available fruit of plant communities. Also, seed addition experiments were performed considering fruit and seed abundance at two different spatial scales: a local scale (50 metres around each plot) and a landscape scale (the 430 ha of the entire study site).

Were there any problems setting up the experiment and gathering your data?

Sure! Our experiment was carried out in cattle pastures, and in the first week of the study, two bulls fighting destroyed one of the experimental plots entirely. In addition, they left some mountains of poops as odorous regards. Fortunately, it happened at the beginning of the study and we could fix the plot quickly with no other inconveniences.

Were you surprised by anything when working on it?

Grey kingbird carrying a fruit of Cupania americana
Grey kingbird carrying a fruit of Cupania americana

We were surprised by two things: First, birds in the study behaved very well! They spent a lot of time at experimental perches and delivered a great amount of seeds (especially, seeds for very rare plant species). And second, one morning, when examining seeds attached to the perches, I found a big toad inside the seed trap. The traps were 1.8 metres tall! I would think that was a joke from my advisor, but I was alone in the field… Fortunately, the toad did not eat any seeds (I hope).

Now that this paper has been published, what’s the next step in this field?

This article focused on secondary forest regeneration in open pastures, because a great proportion of the earth’s tropical forests are secondary forests. But we do not yet know if the same phenomenon that we found in our study also applies for plant regeneration within forests, under the existing canopies.

Another question is: What is the relative importance of mutualistic and antagonistic interactions as drivers of species coexistence? Our findings do not rule out the role of antagonistic interactions, but rather, they are complementary. In each ecosystem, both antagonistic and mutualistic interactions occur, and it is necessary to know how they interplay to shape the early plant communities. This is the next step of my research line in this field… If I can get the funds!


About The Author

How did you get involved in ecology?

Aarón González‐CastroWhen I was an undergraduate student at University of La Laguna (Canary Islands) I joined Dr Nogales’ lab at the Island Ecology and Evolution Research Group. This group called my attention because its research interest was focused on processes as drivers of biodiversity maintenance, rather than describing species as isolated elements of the biodiversity. I started by helping in an PhD thesis about secondary seed dispersal by predatory birds, and then I got engaged in the research on mutualistic interactions. Lastly, reading papers by Pedro Jordano, Carlos M. Herrera and Henry F. Howe during my PhD were the definitive reasons to get trapped in the science of mutualistic interactions.

What’s your current position?

After several years wandering in Universities abroad and doing research as a freelancer, I came back to the Island Ecology and Evolution Research Group/Grupo de Ecología y Evolución en Islas as a postdoctoral researcher. There, I am investigating the relative importance of pollination and seed dispersal as determinants of natural regeneration in plants. I am also acting as an external consultant for technicians and biodiversity managers at the local administration (Cabildo de Tenerife).

What is the worst thing about being an ecologist?

Learning new statistical methods for data analyses. And dealing with some anonymous reviewers, too.

What is the best thing about being an ecologist?

Keeping in contact with nature… And dealing with some anonymous reviewers, of course!

What do you do in your spare time?

Besides hiking in the mountains, I like to read (non-scientific literature) and to spend time with family and friends.


Resumen en español.

Este artículo analiza cómo las aves frugívoras son capaces de dejar una “firma” característica en la regeneración de comunidades vegetales. En concreto, el estudio explora cómo la composición y la abundancia de especies vegetales en las nuevas comunidades en formación puede diferir significativamente de lo que cabría esperar en el caso de que las aves seleccionasen los frutos, y por tanto dispersasen sus semillas, de forma aleatoria. Los autores centran su atención en la manera en que este comportamiento no aleatorio de las aves contribuye a la coexistencia de especies vegetales o, lo que es lo mismo, al mantenimiento de la biodiversidad. De este modo, el artículo sugiere que, además de las interacciones antagonistas (herbivoría, depredación de semillas, etc.), las interacciones mutualistas de dispersión de semillas mediadas por aves pueden favorecer la coexistencia de especies vegetales, pues esta dispersión no se reduce a las semillas de especies muy abundantes, sino también las de especies vegetales más escasas en la comunidad. Back to Insight.