Data and R code for: Temperature-induced multispecies cohort effects in sympatric snakes

In reptiles, reproductive maturity is often determined by size rather than
age. Consequently, growth early in life may influence population dynamics
through effects on generation time and survival to reproduction. Because
reproductive phenology and pre- and post-natal growth are
temperature-dependent, environmental conditions may induce multi-species
cohort effects on body size in sympatric reptiles. I present evidence of
this using ten years of neonatal size data for three sympatric viviparous
snakes, Dekay’s Brownsnakes (Storeria dekayi), Red-bellied Snakes (S.
occipitomaculata) and Common Gartersnakes (Thamnophis sirtalis).
End-of-season neonatal size varied in parallel across species such that
snout-vent length was 36-61% greater and mass was 65-223% greater in years
when gestating females could achieve higher April-May (vs. June-July or
August-September) operative temperatures. Thus, temperature had a larger
impact during follicular enlargement and ovulation than during gestation
or post-natal growth. Multi-species cohort effects like these may affect
population dynamics and increase with climate change.