Hare surveys usually use direct observation methods, such as line-transect Distance sampling, to estimate population densities and abundance. These couldn’t be calculated from camera trap data as hares don’t have individually identifiable markings (e.g. tigers). In 2008, a method was developed which allowed the calculation of population estimates from camera data, regardless of whether researchers could tell individuals apart (Random Encounter Modelling). We used this method to look at densities of European and Irish hares across Mid-Ulster, developing a simple method of data extraction and running analyses to reduce survey effort while maintaining model precision, in the process.
We found that the European hare had almost entirely displaced the Irish hare from the core of its range. Similar patterns were found in both camera trap and Distance sampling estimates. This is a good indication that we observed a invasive-native species replacement process in action. We also found that survey effort could conceivably be almost halved, without substantially compromising the models. This could have important implications for subsequent studies and long-term monitoring of the situation.
Caravaggi A, Zaccaroni M, Riga F, Schai-Braun SC, Dick JTA, Montgomery WI, Reid N (2016) An invasive-native mammalian species replacement process captured by camera trap survey Random Encounter Models. Remote Sensing in Ecology and Conservation. 2: 45-58. doi: 10.1002/rse2.11
Data used in this study are available at:
Caravaggi A (2016): Camera traps capture species replacement. figshare. https://doi.org/10.6084/m9.figshare.1422040.v1