Intercontinental Convergence of Stream Fish Community Traits along Geomorphic and Hydraulic Gradients

Abstract

Abstract. Community convergence across biogeographically distinct regions suggests the existence of key, repeated, evolutionary mechanisms relating community characteristics to the environment. However, convergence studies at the community level often involve only qualitative comparisons of the environment and may fail to identify which environmental variables drive community structure. We tested the hypothesis that the biological traits of fish communities on two continents (Europe and North America) are similarly related to environmental conditions. Specifically, from observations of individual fish made at the microhabitat scale (a few square meters) within French streams, we generated habitat preference models linking traits of fish species to local scale hydraulic conditions (Froude number). Using this information, we then predicted how hydraulics and geomorphology at the larger scale of stream reaches (several pool-riffle sequences) should quantitatively influence the trait composition of fish communities. Trait composition for fishes in stream reaches with low Froude number at low flow or high proportion of pools was predicted as nonbenthic, large, fecund, long-lived, nonstreamlined, and weak swimmers. We tested our predictions in contrasting stream reaches in France (n ϭ 11) and Virginia, USA (n ϭ 76), using analyses of covariance to quantify the relative influence of continent vs. physical habitat variables on fish traitsThe reach-scale convergence analysis indicated that trait proportions in the communities differed between continents (up to 55% of the variance in each trait was explained by ''continent''), partly due to distinct evolutionary histories. However, within continents, trait proportions were comparably related to the hydraulic and geomorphic variables (up to 54% of the variance within continents explained). In particular, a synthetic measure of fish traits in reaches was well explained (50% of its variance) by the Froude number independently of the continent. The effect of physical variables did not differ across continents for most traits, confirming our predictions qualitatively and quantitatively. Therefore, despite phylogenetic and historical differences between continents, fish communities of France and Virginia exhibit convergence in biological traits related to hydraulics and geomorphology. This convergence reflects morphological and behavioral adaptations to physical stress in streams.This study supports the existence of a habitat template for ecological strategies. Some key quantitative variables that define this habitat template can be identified by characterizing how individual organisms use their physical environment, and by using dimensionless physical variables that reveal common energetic properties in different systems. Overall, quantitative tests of community convergence are efficient tools to demonstrate that some community traits are predictable from environmental features.

Hydromorphological conditions, potential fish habitats and the fish community in a mountain river subjected to variable human impacts, the Czarny Dunajec, Polish Carpathians

“…The observed relations between the abundance and species richness of fish in the Czarny Dunajec and physical characteristics of the channel probably reflect genuine links between channel morphology, habitat conditions and riverine communities (Lamouroux et al, 2002;Smiley and Dibble, 2005;Dauwalter et al, 2008). This study documented the dependence of the number of fish species and specimens on the variability in water depth (and also in grain size of bed material in the case of fish abundance), while their dependence on an aggregated width of lowflow channels was not confirmed.…”

The Land-Cover Cascade: Relationships Coupling Land and Water

“…For example, stream fishes have been linked to hydrologic patterns (Poff and Allan 1995), geomorphic features (Lamouroux et al 2002), and habitat stability (Richards et al 1996). For example, stream fishes have been linked to hydrologic patterns (Poff and Allan 1995), geomorphic features (Lamouroux et al 2002), and habitat stability (Richards et al 1996).…”

Tributary streams create spatial discontinuities in habitat, biological productivity, and diversity in mainstem rivers

“…For example, Yu and Peters (1997) found that fish in the Platte River, Nebraska, showed preferences for specific ranges of Fd, with some species found only at localities where Fd ≈ 0, Fd < 0.2, or Fd < 0.3. Lamouroux et al (1999Lamouroux et al ( , 2002 and Lamouroux and Jowett (2005) have demonstrated a strong link between the trait composition of fish assemblages and reach-averaged Froude numbers. This link reflects the general association of low Fd (<0.2) with pool habitats and high Fd (>0.4) with riffle and glide habitats (Jowett 1993).…”