In this ‘Behind the Paper’ post, author Cristóbal Anguita – a researcher at the Wildlife Ecology Laboratory at the University of Chile – discusses his article “When is the bait worth the risk? A mechanistic model of a compensatory ecological trap in seabirds“. Cristóbal explores the concept of a compensatory ecological trap, the challenge of operating at very different timescales, and the importance of taking the time to understand a problem properly, explore its mechanisms and allow a research question to mature.
A Spanish translation of this blog post is available here.
About the paper
Fisheries can provide a highly attractive source of food for seabirds. Discards and other resources associated with fishing vessels are abundant and predictable, potentially making foraging easier and even increasing reproduction or recruitment. But those same vessels can also represent an important source of mortality through accidental bycatch.
Our paper started from a relatively simple question. What happens when an environment provides real short-term benefits while simultaneously increasing mortality risk?
We approached this question through the concept of a compensatory ecological trap. Ecological traps occur when animals continue to use attractive environments that ultimately reduce their fitness. In our case, the situation is particularly interesting because the risky environment is not necessarily “bad” in every respect. Food subsidies can improve foraging success and potentially increase recruitment, while bycatch mortality simultaneously reduces survival.
To explore this mechanism, we developed a spatially explicit, bioenergetic individual-based model. Individuals move, forage, gain and spend energy, reproduce and die. They also use their previous foraging experience to inform subsequent decisions. This means that the ecological trap is not imposed directly in the model. Instead, it can emerge from interactions among foraging success, memory, subsequent habitat use and mortality.
One of our main findings was that short-term benefits can conceal long-term demographic costs. When mortality risk was low, subsidies could increase recruitment and favour population growth. However, once mortality exceeded certain thresholds, those same subsidies continued to reinforce the use of risky areas, increasing exposure to mortality and ultimately causing population declines.
Life history also mattered. Slow-living strategies, such as those typical of albatrosses, were particularly vulnerable because losses in survival are difficult to compensate for through increased reproduction. Faster life histories were more resilient and, under low mortality, could even benefit demographically from subsidies.
Beyond seabirds and fisheries, our results suggest that human-provided resources should not be evaluated only in terms of their immediate benefits. Landfills, supplementary feeding, crops, fishery discards and other anthropogenic resources can modify animal behaviour while simultaneously exposing individuals to new risks. Understanding these interactions between behaviour and demography is therefore essential for assessing their real ecological consequences.
About the research
This study formed the second chapter of my PhD thesis and grew out of a broader question about how interactions between seabirds and fisheries can develop into ecological traps.
In the first stage of my PhD, we approached this problem from a comparative perspective. We asked which seabirds are more likely to exploit resources provided by fisheries and which, at the same time, are most vulnerable to bycatch. That work revealed a particularly strong association among slow-lived species such as albatrosses and led us to a question that could no longer be answered from those patterns alone. What mechanisms could generate this relationship, and under what conditions could the benefits of food subsidies compensate, or fail to compensate, for the costs of mortality?
The second chapter, which became this paper, was our attempt to address that question mechanistically. Rather than collecting a new field dataset, we developed an individual-based model that allowed us to explicitly represent how foraging, memory, habitat use, reproduction and mortality interact over an individual’s lifetime. We also simulated slow, intermediate and fast life-history strategies to understand why the same combination of subsidy and mortality can have very different consequences among species.
One of the most interesting challenges was connecting processes operating at very different timescales. A movement decision may occur over a few hours, reproductive success is observed over a breeding season, and the population-level consequences of those decisions may take decades to emerge. The individual-based model allowed us to follow this entire chain, from individual foraging decisions to long-term population persistence.
Perhaps the result that surprised me most was that increased recruitment does not necessarily mean that a population is doing better. Under some conditions, the benefits associated with food subsidies could coexist with reduced survival and long-term population decline. This contrast between what initially appears beneficial and what ultimately happens to the population is precisely what makes compensatory ecological traps so interesting.
The next step in my thesis was to bring this theoretical framework into an empirical system. We began combining movement, fisheries, discard, bycatch and demographic data using Black-browed albatrosses and demersal trawl fisheries in southern Chile as our study system. In this way, the thesis progressed from identifying a comparative pattern, to exploring the mechanisms that could generate it, and finally to evaluating those mechanisms in a real system.
About the author
My path into ecology was closely tied to seabirds. Early in my career, I had the opportunity to start working with Alejandro Simeone, who introduced me to the world of seabird ecology and has had a major influence on my scientific development. For seven years, I collaborated with him on seabird monitoring and counts in Valparaíso Bay, central Chile. That experience of long-term, systematic observation gradually led me towards broader ecological questions and eventually to my Master’s thesis on community ecology.
During my PhD, which I completed under the supervision of Alejandro Simeone and Cristián Estades, my interests gradually shifted from describing ecological patterns towards understanding the mechanisms that generate them. In particular, Cristián’s mechanistic approach to ecological questions had an important influence on the way I began using individual-based models. It encouraged me to think more explicitly about how individual processes such as movement, habitat selection and resource use can scale up to demographic and population-level consequences.
In many ways, my current research brings these two influences together. One is the natural-history perspective and seabird ecology that I have developed through my work with Alejandro. The other is the mechanistic modelling perspective that I developed with Cristián. I am currently a researcher at the Wildlife Ecology Laboratory at the University of Chile, where I am particularly interested in the interface between individual behaviour and population dynamics, with a focus on movement, habitat selection and maladaptive behaviour in human-modified systems.
My current scientific obsession is precisely this kind of maladaptive behaviour. I am particularly interested in situations where animals respond in apparently sensible ways to environments altered by human activities, but those same decisions ultimately produce unexpected consequences. Ecological traps are a particularly clear example of this problem.
Outside research, one of my favourite things to do is trekking in the Chilean Andes. But I also really enjoy something much simpler, which is spending time at home with my partner, Manuela Mege, and our cats. I enjoy cooking, gardening and slowly working through the seemingly endless list of things that still need fixing or improving around our house. After spending many hours working with models, code and data, both walking in the mountains and taking care of these everyday things are good ways for me to disconnect.
In my experience, one of the main barriers to developing a scientific career in Chile is the relatively low level of public investment in science and research. This translates into limited funding opportunities and a highly competitive academic job market, while also creating considerable pressure on early-career researchers to maintain constantly high levels of productivity.
For that reason, if I could give one piece of advice to my younger self, it would be to think less about productivity and focus more on the depth of the questions. Over time, I have increasingly come to value the idea of slow science. I think it is worth taking the time to understand a problem properly, explore its mechanisms and allow a research question to mature, rather than measuring scientific progress mainly through the number of outputs or publications.
