Elevation and latitude interact to drive life-history variation in precocial birds: a comparative analysis using Galliformes

Elevational gradients provide a powerful laboratory for understanding the environmental and ecological drivers of geographic variation in avian life-history strategies. Environmental variation across elevational gradients is hypothesized to select for a trade-off of reduced fecundity (lower clutch size and/or fewer broods) for higher offspring quality (larger eggs and/or increased parental care) in higher elevation species and populations. In birds, a focus on altricial species from north temperate latitudes has prevented an evaluation of the generality of this trade-off, and how it is affected by latitude and intrinsic factors (development mode). We performed a comparative analysis controlling for body size and phylogenetic relationships on a global data set of 135 galliform species to test (i) whether higher elevation precocial species have lower fecundity (smaller clutch and/or fewer broods) and invest more in offspring quality (greater egg mass) and (ii) whether latitude influences...