This blog post is provided by Mark Rademaker, Anieke van Leeuwen and Isabel Smallegange and tells the #StoryBehindthePaper for the paper “Why we cannot always expect life history strategies to directly inform on sensitivity to environmental change“, which was recently published in Journal of Animal Ecology. In their paper, they explore individual-level tradeoffs, and how these affect trait patterns and population responses, finding that compared to classical models of life history traits we should not underestimate the impact of the unique life histories experienced by each individual in shaping large-scale population response patterns.

Life on earth is highly diverse, and each species is equipped with different traits that enhance their survival and reproduction. These traits depend on both the species’ evolutionary history and the environment they live in. This life history diversity can be grouped along a spectrum ranging from species with ‘fast’ to ‘slow’ life histories. On the fast end of this spectrum are species that develop quickly, produce lots of offspring, but live shortly, such as houseflies (1-2 months). On the slow end are species that take a long time to grow and produce few offspring, but live long lives, such as the Greenland shark (> 250 years).

Scientists have observed a correlation between a species’ life history speed and its projected sensitivity to changing environments. Species with slower life histories are less affected by variable conditions than those with faster life histories. This ‘classic’ result is important because (1) we expect environmental conditions to become more variable due to climate change, and (2) a few traits are sufficient to indicate how fast/slow the life history of a species is, and therefore how sensitive their populations might be to these changes.

Studies use demographic models to link traits to population responses, but most of these models overlook an important aspect – the variation in traits observed between individuals. This variation arises from trade-offs that individuals face during their lifetime. The question is thus whether including such individual-level tradeoffs matters when examining large-scale population response patterns? The current working assumption is that it does not, and our study puts this assumption to the test.

We used a comprehensive dataset of traits from ray-finned fish, a diverse group of vertebrates with various life history strategies. After applying a demographic model that considers individual-level tradeoffs, we then tested how these tradeoffs affect trait patterns and population responses. We used a special type of PCA analysis to examine how trait patterns and the sensitivity of populations to environmental change link together. We observed that trait patterns still fall along a spectrum ranging from fast to slow life histories.  However, the ‘classic’ link between speed of life and sensitivity to changing environments disappeared when we accounted for individual tradeoffs. Some fish species are more sensitive to environmental change, and others less, but there is no simple rule predicting this outcome.

The old saying that ‘all roads lead to Rome’ means that there are many ways to achieve the same outcome. Our results indicate the same can be said of traits: there are many combinations that can make a population sensitive or insensitive to climate change. Furthermore, our outcomes highlight that we should not underestimate the impact of the unique life histories experienced by each individual in shaping large-scale population response patterns. A conceptual visualization of the main results is provided below.

Read the paper

Read the full paper here: Rademaker, M., van Leeuwen, A., & Smallegange, I. M. (2024). Why we cannot always expect life history strategies to directly inform on sensitivity to environmental change. Journal of Animal Ecology, 00, 1–19. https://doi.org/10.1111/1365-2656.14050