A survey of freshwater fishes and their macroparasites in the ... - NINA

4.2 Fish communities
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NINA Report 635
4.2.1 Species diversity vs.altitude
Although the altitudinal distribution of our sampling sites differ between the Pacific and the Atlantic
slopes, in both cases there are clear negative correlations between the altitude of localities
and the number of fish species present (Figure 3). All localities where our samples contained
four species or less were more than 400 m above sea level. On the Atlantic slope, four
localities with more than ten species were at 350 m a.s.l. or less. On the Pacific slope, two of
our low-lying localities (< 200 m a.s.l.) had more than 10 species of fish. Three Pacific slope
rivers (Rio Murcielago, Rio Potrero Grande, and Rio Poza Salada) had comparatively few species
of fish. These are all more or less seasonal rivers with small catchment areas, containing
only small pools of water in the dry season. It may be noted that the gradients of the two regression
models (excluding the seasonal rivers) are not significantly different, that is, the effect
of change in altitude on the number of fish species is of the same magnitude along both
slopes. The different intercepts (“number of species at sea level”) is in accordance with the fact
that the fauna on the Pacific side of the watershed is poorer in species (cf. Smith & Bermingham
2005). The common gradient for the two slopes (again excluding the seasonal rivers) is -
0.024 (N=18; R 2 =0.74), so we would expect to “loose” one species for every 42 meters increase
in altitude.
No. fish species
0 5 10 15 20
2
Atlantic slope
3
7
0 100 200 300 400 500 600 700
20
18 28
Altitude [m a.s.l.]
10
Y = 18.7 - 0.025 X
21
8
9
22
No. fish species
0 5 10 15 20
Pacific slope
0 100 200 300 400 500 600 700
Altitude [m a.s.l.]
Figure 3 Recorded number of fish species versus altitude in ACG rivers draining to the Atlantic
(left) and to the Pacific (right). Numbers on data points refer to locality number in Table 1 and
Figure 1. For localities on the Atlantic slope, we have R 2 = 0.67. For the Pacific slope, the dotted
regression line concerns localities with permanent water (N = 7; R 2 = 0.87), whereas the
bold line represents all localities (N = 10; R 2 = 0.54), including the low-lying small watersheds
with seasonal water (locs. 5, 12 and 23). All regressions are significant (p < 0.05).
4.2.2 Fish community structure
The diet of the fish species indicates the trophic position of the species (i.e. the position of the
species in the aquatic food web at the locality). It may also indicate the potential load of parasite
species transmitted through the food chain. We did not, however, detect any indication that
parasite fauna of the host species reflecting the trophic ecology of the host.
The diet types of the fish species recorded in the localities of ACG are listed in Table 3. The
diet classes are: detritus (dead organic material), fresh plant material, invertebrates, and fish.
The classification of species according to diet is based on information in the literature and our
own observations. The majority of species (29 spp.) include invertebrates and/or fish in their
12
5
11
23
4
27
Y = 14.3 - 0.022 X
Y = 9.7 - 0.013 X
19 6,16
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