Fish habitat association in an Ozark stream. Henry L. Bart, Jr. Department of Zoology, University of Oklahoma, Norman, OK 73019, U.S.A.. Present address: ...
Environmental Biology of Fishes Vol. 24, No. 3, pp. 173-186, 1989 0 Kluwer Academic Publishers, Dordrecht.
Fish habitat association in an Ozark stream Henry L. Bart, Jr. Department of Zoology, University of Oklahoma, Norman, OK 73019, U.S.A. Present address: Department of Ecology, Ethology and Evolution, University of Illinois, U.S.A. Received 6.11.1986
Urbana, IL 61801,
Accepted 14.3.1988
Key words: Habitat guilds, Assemblage structure, Fauna1 similarity, Constancy, Stream fishes, North America Synopsis
Associations of fishes in physically distinct habitats (riffles, inlets and pools) of Flint Creek were studied to evaluate critically the habitat-guild concept-the notion that fishes associate with patches of stream habitat in discrete groups. There was little evidence of significant interspecific association at the habitat level. Most fishes were very generalized in their habitat-use patterns. Fauna1 similarity between habitats was unrelated to physical-habitat similarity. Assemblages from physically distinct habitats were little different from those from physically similar habitats. The structure of the associations (constancy within groups of commonly occurring species) varied seasonally and from site to site. There were constant associations in pools from summer through fall and this coincided with conditions of high fish density and low food availability, suggesting that the pattern resulted from past or present interaction between species. However, the timing also coincided with recruitment of young. Pools were the favored habitats of young-of-year fishes which dominated assemblages in these areas during summer and fall months. This apparently adaptive pattern of habitat association, operating in tandem with local reproductive success could have been responsible for the constancy observed in pools. Most of the species considered here made use of a variety of habitat conditions over the course of their life histories. Individual patches of habitat satisfied the needs of few fish, and thus, seemed too small a scale for the study of community-assembly mechanisms. There was better evidence of interspecies association at the scale of two or more of these habitat areas combined.
Introduction
There is a predictable pattern to variation in stream-channel morphology (Schlosser 1982), with most of the variability expressed in spatially recurring patches of habitat such as riffles and pools (Leopold et al. 1964). Stream fishes are believed to be associated with these habitats in discrete groups (so-called ‘habitat guilds’, Gorman & Karr 1978, Schlosser 1982)) associations forged by adaptation and interspecific interaction. Herbold (1984) found
evidence of long-term constancy in abundance relationships and ‘niche diversification’ when he partitioned an otherwise ‘stochastic’ fish assemblage (Grossman et al. 1982) in this way. Although the study is controversial (Grossman et al. 1985, Whittier & Miller 1986), it suggests that stream fish communities are structured by interactions occurring at the habitat level. The notion of fish-habitat guilds in streams though intuitively appealing (Grossman et al. 1985) - has yet to be critically evaluated. There is some
174 question as to whether this is an appropriate way to group species. Fish textbooks (cf. Whittier & Miller 1986) and studies of fish population structure along stream-size gradients (e.g. Anderson 1985) suggest that fishes can be very generalized users of stream habitat, contrary to an earlier opinion that habitat specialization may be the rule (Gorman & Karr 1978). If fishes normally occur across several different habitats, as this evidence alternatively suggests, then interactions occurring within habitats, and any associations formed as a result of those interactions, would be of only limited significance to stream fish community structure. 1 studied fish-habitat association in an Ozark stream to test the habitat-guild concept and to determine the importance of structuring at the habitat level. 1 measured fauna1 similarity between three habitats with different physical characteristics, and related it to the physical similarity between habitats; 1 compared seasonal census and removal samples from each habitat to test the constancy of association within groups of commonly occurring species; 1 examined trends in age distribution, fish density and resource availability in an effort to determine the underlying basis for the patterns observed; finally, 1 considered the pattern of association at an expanded spatial scale (the scale of the three habitats combined), and what it suggested about fish-community structure in streams.
Brazilian waterweed, Elodea densa, and a variety of types of algae. In backwater areas, stands of waterweed are typically interspersed with patches of watermoss, Fontinalis sp., pondweed, Potomogeton amphifolius, and coontail, Ceratophyllum demersum. Water willow, Justicia americanum, and watercress, Nasturtium officinale, form dense growths along the stream margins during summer and fall. Duckweed, Lemna trisulca, blankets the surface of backwaters during spring. The stream is well shaded from late spring to early fall by a galleria forest that includes sycamore, Platanus occidental& elm, Ulmus americanum, and hackberry, Celtis occidentafis, among other types of trees. The study sites were chosen because each contained three distinct habitats - mainchannel riffle, and backwater inlet and pool-with nearly identical arrangements, and presumably shaped by the same physical forces. Riffles at all three sites were part of larger gradient areas; inlets and pools combined to form the backwaters which were always lateral to the riffles. Pools were rounded, spring-fed habitats with very slight outflow. Inlets were basically channels which connected the pools to the mainstream, always entering at the base of the riffles. At one of the sites (site 3), the pool was part of a more extensive backwater system created by beavers. All of the habitats were shallow (rarely deeper than 1 m) and relatively free of obstructions like treefalls and large rocks. This made them much easier to sample than mainchannel pools and raceways.
The study area The study was conducted at three sites along a 5 km stretch of Flint Creek - a third-order tributary of the Illinois River located in northeastern Oklahoma (Delaware County). Flint Creek drains western portions of the Ozark Plateau bordering Arkansas and Oklahoma. The hilly topography of eroded limestone outcroppings (Blair & Hubble 1938) produces a fairly high gradient in the watershed. Numerous associated springs provide a permanent flow of clear, cool water. The physical environment is benign, for the most part, but like other streams in the region (Ross et al. 1985, Matthews 1986), Flint Creek experiences brief periods of severe flooding. Aquatic vegetation consists mainly of
Methods 1 sampled fishes in the nine habitats (riffles, inlets and pools at the three sites) monthly from March 1983 to May 1984 - a sampling period that covered five seasons (two springs, summer, fall and winter). Within each season, 1 made two routine ‘censusrelease’ samples, and one ‘high-effort’ removal sample (taken in the month between the two censuses). The purpose of the removal was to capture or displace all of the fish in an area in addition to gaining information on abundance relationships at the time of removal. The censuses allowed me to compare abundance relationships before and after
175 were taken in two to four seine hauls. The rank order of species abundances after just one or two seine hauls was strongly correlated (P
