4.2 | Core species niche overlap and breadth
Most species demonstrated an increase in the overlap of their niche into
another between time periods. Of the 20 species pairs, 16 had a
probability ≥ 0.89 of an increase in their niche overlap (Table 3).
Between periods and among all species, mean niche overlap increased by
35.7%. For a given species, increases in niche overlap was highest for
Channel Catfish (mean = 51.3%), followed closely by Colorado Pikeminnow
(49.5%) and Speckled Dace (46.3%); whereas Fathead Minnow (25.4%) and
Flannelmouth Sucker (6.1%) showed limited increases in niche overlap.
For Colorado Pikeminnow, the largest niche overlap increase was into the
niche of Fathead Minnow (67.3%) and the least was into Channel Catfish
(37.3%). For these nonnative fishes, niche overlap into Colorado
Pikeminnow did not likely change between time periods (Fathead Minnow =
0.25 and Channel Catfish = 0.63 probability).
With a probability ≥ 0.90, the niche breadth of four of the five core
species changed between the historical and contemporary period (Table
4). Species with the largest niche breadth declines were Colorado
Pikeminnow (72%) and Speckled Dace (33%). Whereas Flannelmouth Sucker
niche breadth likely increased by 165% and Fathead Minnow by 126%. A
change in niche breadth was least likely (probability = 0.81) for
Channel Catfish. Between periods and among species, the largest core
niche breadth was historical Colorado Pikeminnow (SEABmean = 7.59 and 95% CI = 3.29 – 17.04). Colorado Pikeminnow’s niche
breadth may have been greater than all other historical species analyzed
as only the size of Speckled Dace’s niche breath slightly overlapped
(3.00, 1.72 – 5.31). The smallest historical niche breadth observed was
Channel Catfish (1.25, 0.73 – 2.15) followed closely by Roundtail Chub
(1.29, 0.71 – 2.33). In the contemporary period, the largest niche
breadth occurred in Flannelmouth Sucker (5.31, 3.49 – 8.08), followed
by two species that had similar sized niche breadth, Red Shiner (4.32,
3.64 – 5.14) and Fathead Minnow (4.31, 3.07 – 5.97). Contemporary
Channel Catfish continued to have the smallest niche breadth (1.58, 1.35
– 1.85).