Reciprocal Subsidies in Sub-Alpine Ponds and the Influence of a Range-Shifting Caddisfly

Subsidies, or the exchange of resources derived from one ecosystem to adjacent ecosystems is an integral process for the function of food webs. However, this phenomenon is variable based on both landscape and community factors. Throughout my thesis, I explore how subsidy characteristics in a sub-alpine pond landscape called the Mexican Cut Nature Preserve (MCNP), located in Western Colorado. In Chapter 1 I introduce the broad concepts surrounding subsidies across ecosystems, I then highlight the important landscape factors of the MCNP. In chapter 2 I examine the balance of reciprocal subsidies i.e., subsidies imported and exported from ponds. The overall sum of imports and exports was lower in the sub-alpine landscape when compared to low elevation studies. Terrestrial insect imports were the largest subsidy which deviates from low elevation studies which are often dominated by leaf litter. Chapter 3 takes a closer look at subsidy exports from ponds via the emergence of aquatic insects focusing on the influence of a native range shifting caddisfly Nemotaulius hostilis on subsidy timing, magnitude and duration. I found that range shifting N. hostilis introduced an early season subsidy pulse which likely persists in the terrestrial landscape for a substantial period of time, enriching pond subsidy export.