Ecotone Study: Plant Above Ground Net Primary Productivity by Site

Dataset consists of the annual aboveground net primary production (ANPP) across 3 habitats grouped by plant form and total ANPP. The habitats are grassland, mesquite shrubland, and the ecotone between the 2. The plant forms are winter annual forb, annual forb, bi-annual forb, perennial forb, annual grass, perennial grass, shrub, and sub-shrub. OBJECTIVE: The purpose of the study is to investigate how pulses of precipitation translate into pulses of plant aboveground net primary productivity (NPP) and how the small mammal community responds to such changes also in relation to shrub gradient across the landscape. Particularly we are interested in how the energy flows through the ecosystem in response to pulses of rain, how the small mammal community partition resources (in terms of C3 (forbs and shrubs) and C4 (grasses) plants) and how the genetic structure of some species (e.g., Dipodomys spp.) is affected by their population dynamics. HYPOTHESES: 1) Small mammal abundance should respond positively to precipitation and NPP. 2) On a temporal scale, the small mammal energy use should show parallel fluxes along the shrub gradient. 3) The small mammal community should consume C3 and C4 plants according to their availability (or NPP). 4) At low population density, dispersal should be limited and the genetic variance will be distributed among populations rather than within (i.e., Fst will trend towards higher values). After pulses of rain and NPP, population densities will be greater, dispersal prevalent, and the genetic variance of populations will be distributed within populations (i.e., Fst will approach zero) as dispersal homogenizes populations. Total aboveground annual net primary productivty is calculated for winter annual forb, annual forb, bi-annual forb, perennial forb, annual grass, perennial grass, shrub, sub-shrub, and the total of these.