##Thesis Outline

Working Title: Validating Estimates of Core versus Transient Site Occupancy in North American Birds

Working Hypotheses:

1. Expect to see a higher frequency of transient species when additional datasets consulted (BBC) outside of the BBS data alone.
2. Expect to see continued or strengthened support for regional-scale variables predicting transient species presence.
3. Expect to see continued or strengthened support for local-scale variables predicting core speceies presence (Coyle et al. 2013).

Background

Biodiversity research is critical to the ongoing goals of ecologists to make informed and cost-effective conservation management decisions. In order to understand biodiversity, it may be advantageous to approach analysis from a community structure perspective. A “core-transient” model has emerged in an effort to better quantify the diversity of communities, and may better reflect spatiotemporal changes in the community and habitat than traditional models. The core transient model is also more reliably and easily derived than models that rely on designations of commonness and rarity (Coyle et al 2013).

A designation of “core” or “transient” is based on verifiable occupancy of a species in a habitat, where occupancy designates the sustained use of and presence in a habitat. Occupancy can be measured as a distribution of the proportion of time spent present in a particular site. When plotted, this distribution is often strongly bimodal (Coyle et al. 2013), suggesting that species may fall into one of two categories. Transient species characterize the low end of the bimodal distribution. These species spend a very small proportion of time at a given site, utilizing little of the habitat in any consistent manner (Dolan et al. 2009, Gaston 2010). Species that spend a large proportion of time present at a given site may be designated as its core inhabitants. The two designations may bear utility in efforts to better understand the variables that influence biodiversity estimates and species richness, in tandem with environmental variables.

Normalized difference vegetation index (NDVI) has been suggested as a predictor of bird-species richness for multiple habitat types, and as a predictor for local environmental contributions to variations in richness. (Coyle et al. 2013, Nieto et al. 2015). These local contributions may affect core and transient species differently, and reflect differences in the proportion of core to transient species present at a given site (Belmaker 2009; White and Hurlbert 2010, Coyle et al. 2013).

Accomplished To-date:

1. Pilot analysis comparing measures of core and transient species richness between BBS (all) and BBC (1992) datasets based on site pairings across minimum geographic distance.
   a) Geographic distance doesn't explain discrepancies between datasets.

Road Map Forward:

1. Compare measures at paired sites based on minimum environmental distance.