Functional analysis of Normalized Difference Vegetation Index curves reveals overwinter mule deer survival is driven by both spring and autumn phenology

Abstract

Large herbivore populations respond strongly to remotely sensed measures of primary productivity. Whereas most studies in seasonal environments have focused on the effects of spring plant phenology on juvenile survival, recent studies demonstrated that autumn nutrition also plays a crucial role. We tested for both direct and indirect (through body mass) effects of spring and autumn phenology on winter survival of 2315 mule deer fawns across a wide range of environmental conditions in Idaho, USA. We first performed a functional analysis that identified spring and autumn as the key periods for structuring the among-population and among-year variation of primary production (approximated from 1 km Advanced Very High Resolution Radiometer Normalized Difference Vegetation Index (NDVI)) along the growing season. A path analysis showed that early winter precipitation and direct and indirect effects of spring and autumn NDVI functional components accounted for 45% of observed variation in overwinter survival. The effect size of autumn phenology on body mass was about twice that of spring phenology, while direct effects of phenology on survival were similar between spring and autumn. We demonstrate that the effects of plant phenology vary across ecosystems, and that in semi-arid systems, autumn may be more important than spring for overwinter survival.

Coastal Geomorphological and Land Use and Land Cover Study on Some Sites of Gulf of Kachchh, Gujarat, West Coast of India using Multi-Temporal Remote Sensing Data

“…Here, the result of the index can range from -1 to +1. Vegetated surface gave positive value, the soil may have near zero and for water features negative value obtained (Defries & Townshend, 1994;Hurley et al, 2014). In our study, NDVI result presented non-significant variation between decade intervals.…”

“…The resulting index can range from -1 to +1 in which vegetation surface gave positive, soil near about zero and water features have negative values (Hurley et al, 2014;Tucker, 1979).…”

Asynchronous vegetation phenology enhances winter body condition of a large mobile herbivore

“…Emerging evidence suggests that limits set by ANPP are modified by the spatial pattern and timing of plant growth. In particular, there is evidence that heterogeneity in plant communities expressed over space, particularly heterogeneity that induces variation in time by influencing plant phenology, offers fundamentally important nutritional benefits to foraging herbivores that enhance the performance of individuals and their populations (Pettorelli et al 2007;Hebblewhite et al 2008;Mysterud et al 2008, Searle et al 2010Giroux et al 2014, Hurley et al 2014, Iversen et al 2014. For instance, fine scale dynamics of vegetation green-up across landscapes may determine the length of time during spring when high quality forage is available for ungulates.…”

“…The condition of ungulates in winter is an important determinant of future fitness because of its impact on individual body condition at the start of the breeding season (Forchhammer et al 2001;Steinheim et al 2002;Solberg et al 2007;Rodriguez-Hidalgo et al 2010;Taillon et al 2012;Hurley et al 2014). In this paper, we mechanistically link changes in annual weather patterns and variation in the spatial and temporal patterns of plant phenology across landscapes with the winter body condition of adult female mule deer to facilitate understanding of how changing weather patterns may affect this important species.…”

“…More specifically, we predicted that individuals inhabiting home ranges with shallower vegetation green-up slopes (slower aggregate rate of vegetation green-up) would experience elongated periods when the vegetation is at peak 6 quality, and that this benefit would accrue during the spring and carry over to winter months resulting in better subsequent winter body condition for these individuals in comparison to those inhabiting home ranges with steeper vegetation green-up slopes (Pettorelli et al 2005c;Lendrum et al 2013;Hurley et al 2014). We also predicted that individuals inhabiting home ranges with an earlier vegetation onset (i.e., a higher value of NDVI in early spring) would have higher winter body condition than individuals occupying home ranges with a later vegetation onset (Pettorelli et al 2005c).…”