SPM Journal Club: Demographic buffering of life-histories
The demographic buffering hypothesis states that the temporal variation in vital rates is smaller the more these vital rates contribute to fitness. The pattern is appears well supported, but recent evidence indicates that life histories may be buffered or labile, and that there is a phylogenetic signal in this.
We discuss a very recent paper published early this year in Nature, which uses statistical scaling to investigate evidence of the demographic buffering hypothesis in plant life histories. The study shows that widespread evidence for demographic buffering may often be an artefact, and that in truth, there exists a wide variety of both buffered and labile life histories across the plant kingdom.
One of the best-supported patterns in life history evolution is that organisms cope with environmental fluctuations by buffering their most important vital rates against them. This demographic buffering hypothesis is evidenced by a tendency for temporal variation in rates of survival and reproduction to correlate negatively with their contribution to fitness. Here, we show that widespread evidence for demographic buffering can be artefactual, resulting from natural relationships between the mean and variance of vital rates. Following statistical scaling, we find no significant tendency for plant life histories to be buffered demographically. Instead, some species are buffered, whereas others have labile life histories with higher temporal variation in their more important vital rates. We find phylogenetic signal in the strength and direction of variance–importance correlations, suggesting that clades of plants are prone to being either buffered or labile. Species with simple life histories are more likely to be demographically labile. Our results suggest important evolutionary nuances in how species deal with environmental fluctuations.