Overcoming cohort effects in a Mediterranean ecosystem: The role of density and precipitation on southern mule deer body mass

Abstract

Cohort effects on body mass of deer species are caused by both density-dependent and -independent factors. Cohort effects occur in the year of birth and affect body size throughout life. We hypothesized that deer in low latitudes should be able to overcome cohort effects through compensatory or catch-up growth because mild and wet winter conditions are more amenable for animal growth. We analyzed 27 years of mule deer harvest data from Camp Pendleton, California. Using generalized least-squares regression with restricted maximum likelihood estimation to estimate parameters, we determined that eviscerated body mass of southern mule deer (Odocoileus hemionus fuliginatus) was affected by precipitation and relative abundance. We also found that deer were able to recover from periods of poor nutrition and overcome cohort effects by 2.5 years of age, which has not been demonstrated in other ungulate populations. This study demonstrates that body mass can be used as a tool to assess the nutritional state of a population in an environment with high inter-annual variation in biotic and abiotic factors. Further, managers in environments where mild and wet winters extend growing seasons should consider the possibility that deer may be able to recover from periods of missed growth when making harvest recommendations. 2014 The Wildlife Society.