In this week’s blog post, we’re learning all about the causes and consequences of functional generalism! Author Ricardo Sánchez Martín explains the fascinating fit between hummingbirds and the plants they pollinate: “Functional generalism in plant-hummingbird interactions: causes and consequences from a plant perspective”.
Scientists have long been fascinated by the apparent tight fit between hummingbirds and the flowers they pollinate: long-billed birds visit long flowers, while short-billed ones favor short blooms. Yet nature is rarely that simple. Some plant species attract hummingbirds with similar bill lengths, while others are visited by birds spanning a broad range of bill sizes. This difference in the spread of visitor traits is what we call functional generalism.
In this study, we aim to understand both the causes and consequences of functional generalism. Why do plant species differ in the range of bill sizes they can attract? Is this variation explained by the shape of the flowers—their length, openness, and curvature—or by local factors such as how common the plants are, how long they bloom, and which hummingbirds and other flowers are present during their flowering? And what do these differences mean for plant reproduction?
Our findings show that both flower traits and the surrounding plant community influence the degree of functional generalism. Long, narrow flowers drew hummingbirds spanning the widest range of bill sizes. Context mattered too: flowers growing among flowers that had many different shapes attracted a broader range of functionally distinct visitors. Likewise, common plants with short bloom times drew more functionally distinct visitors than rare species that flowered for months.
Having a broader range of functionally distinct visitors was not always better in terms of plant reproduction. Plants visited by hummingbirds with a moderate spread of bill lengths received the most visits, but beyond a certain point, greater functional generalism meant fewer visits overall. Flowers attracting visitors with very different bills were also more likely to experience nectar robbing, when hummingbirds pierce the base of the flower to take nectar without pollinating it.
These results underscore the importance of considering variation when examining ecological interactions. Such flexibility in how species interact can affect not only individual success but also the stability and resilience of entire communities, highlighting the need to better understand these dynamics to improve predictions of ecosystem responses to global change.
2. About the Research
We studied 211 species of hummingbird-pollinated plants across 32 sites in Costa Rica, Ecuador, and Brazil to ask why some flowers attract functionally distinct assemblages of hummingbirds, while others only interact with a tight pool of functionally similar hummingbirds. Answering this question was only possible thanks to a large international collaboration, built on years of coordinated fieldwork by local teams in each country. Bringing these efforts together was a major challenge, but it provided an unprecedented view of how hummingbirds and plants interact in the Neotropics.
We discovered unexpected patterns. Flowers with long, narrow corollas—traits usually seen as barriers that limit access—were actually the ones that welcomed the widest set of functionally distinct hummingbirds. In other words, the flowers that looked the most restrictive turned out to be the most popular.
The next challenge is to see how climate change might influence these patterns. As flowering seasons shift and hummingbird communities change, plants may suffer changes in the pool of available visitors. The variability in the traits of their pollinators will have important consequences for both plants and the future of these tropical communities.
3. About the Author
I have always been fascinated by the complexity of nature—why certain species coexist, how they interact, and how their relationships evolve across space and time. That curiosity led me into ecology: I completed a PhD in Ecology at the Spanish National Research Council (CSIC), and today I am a postdoctoral researcher in the Spatial Evolutionary Ecology group led by Catherine Graham at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).
My research explores different types of mutualistic networks across different environments, from plant–plant recruitment in Mediterranean and North American drylands to plant–hummingbird pollination along tropical mountain slopes in Central and South America. We live in an era of unprecedented environmental change. These changes are expected to shift species’ ranges, but what really fascinates me is how the relationships between species—who competes, who facilitates, who pollinates whom—also shift. These invisible ties can be just as important for the future of biodiversity as temperature or rainfall. You can find more of my work on https://www.researchgate.net/profile/Ricardo-Sanchez-Martin.
Besides science, I love being outdoors, whether it’s hiking in the mountains, skiing in winter, climbing, or just exploring new landscapes. I also enjoy traveling — discovering nature, food and culture in new places always gives me fresh inspiration. When I’m not outside, I enjoy jogging, cooking, and spending time with family and friends.
Like many early-career researchers, funding uncertainty has been one of the biggest challenges. Long-term ecological projects take years of effort and collaboration, but scientific careers often run on short-term contracts and fellowships. Balancing that mismatch can be stressful, but it is essential to enjoy the journey and appreciate the privilege of dedicating yourself to what you love.
