Effects of leaf litter on pond insect colonizers

Here, we examined the effects of leaf litter species on the colonization of aquatic insects, primarily beetles. We also assessed the relative importance of different factors that could be perceived as risk and rewards depending on whether values of that parameter are high or low. These parameters included leaf chemistry, water tannin concentration, and water quality. We placed 42 experimental pools at a field-forest edge to serve as colonization sites. Each pool had leaf litter from one of 14 different species of tree leaves added (all common in the study area), including 13 native tree species and one nonnative (Bradford pear [Pyrus calleryana]) to create artificial ponds with a variety of different leaf chemistries and water quality. Artificial pools (1m diameter, 30cm deep) were established on Louisiana Tech University’s South Campus farm property in three adjacent blocks. Each replicate consisted of leaves from a unique combination of leaf species and site of leaf collection. In total, 14 leaf treatments were randomly assigned a location within each block for three replicates per leaf treatment (i.e., one per block). Mesocosms were placed approximately 1m apart from each other in a field within 1-6m of the forest edge and were filled with tap water to 10cm deep (approximately 80L) on 6-7 May 2018. Each mesocosm was covered with window screen covers (1-2mm mesh diameter) secured with bungee cord immediately after filling, to prevent colonization prior to establishing treatments and were allowed to sit for 24 hours to allow the water to dechlorinate. At the start of the experiment (10 May 2018), 80g of leaf litter from each tree species was added to its corresponding mesocosms, resulting in an overall concentration of 1g leaf litter/L of water for each treatment. All colonizing aquatic insects were collected from each artificial pool twice weekly from 14 May to 9 July 2018. Collecting twice per week and thus continuously removing colonizers allowed us to focus on insect habitat selection and minimize priority effects, the influence of early colonizers on later colonizers. All specimens collected were preserved in 70% ethanol, dated, and later were identified.