Hot Spot Analysis
What is the spatial pattern of juvenile O. mykiss abundance, presence/absence, and survey sites and how do these patterns compare to one another?
I used a hot spot analysis to illustrate these spatial patterns.
- To begin, I queried my data to visualize survey points within 5-year timeframes.
- I ran a hot spot analysis for juvenile steelhead abundance for each window of time in separate maps.
- I then added a presence/absence attribute and calculated the field using the reclassify operator on the steelhead count column. This function categorizes values greater than zero and equal to zero as ones and zeroes respectfully.
The hotspot analysis of abundances did not result in any cold spots, which differed from the analysis of presence/absence data. I am not certain why this would be but speculate that it may be because there is more variability in the abundances. Hotspots in the northern range of the Oregon Coast are consistent in both analyses.
I found this method helpful in visualizing basic trends in these data and assessing the extent to which the sampling design achieved spatially balanced survey site selection. However, I find this method to be fairly “black box” in that it is difficult to identify where these hot spots and cold spots are derived. It is my understanding that these hotspots are based on certain thresholds of p-values and Z-scores, but it is unclear what that threshold is. It is also unclear what distance was used for the fixed distance band, as it is automatically calculated. Due to my surface-level understanding of this method, I would not use it to draw conclusions about my data, but rather to illustrate broad trends.
Kernel Density Plots
What is the spatial pattern of juvenile coho compared to juvenile O. mykiss?
Above is the kernel density analysis of juvenile coho density data from 1998-2020 in the Oregon Coast range. The hot pink circle indicates the only visible area of high kernel density values. Below is the same analysis applied to juvenile O. mykiss abundance data from 2002-2020 also within the Oregon Coast.
In the future I hope to rerun these analysis and adjust the parameters in ArcPro to hopefully yield results which communicate patterns better in the coho dataset. I also think I should create a new variable of O. mykiss density based on abundance per survey length as a way creating a more standardized comparison.