Fish complementarity is associated to forests in Amazonian streams

Bordignon, Carolina Rodrigues; Casatti, Lilian; Pérez-Mayorga, María Angélica; Teresa, Fabrício Barreto; Brejão, Gabriel Lourenço

doi:10.1590/1982-0224-20140157

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Articles • Neotrop. ichthyol. 13 (03) • Jul-Sep 2015 • https://doi.org/10.1590/1982-0224-20140157 linkcopy

Fish complementarity is associated to forests in Amazonian streams

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Abstracts

The functional structure of communities is commonly measured by the variability in functional traits, which may demonstrate complementarity or redundancy patterns. In this study, we tested the influence of environmental variables on the functional structure of fish assemblages in Amazonian streams within a deforestation gradient. We calculated six ecomorphological traits related to habitat use from each fish species, and used them to calculate the net relatedness index (NRI) and the nearest taxon index (NTI). The set of species that used the habitat differently (complementary or overdispersed assemblages) occurred in sites with a greater proportion of forests. The set of species that used the habitat in a similar way (redundant or clustered assemblages) occurred in sites with a greater proportion of grasses in the stream banks. Therefore, the deforestation of entire watersheds, which has occurred in many Amazonian regions, may be a central factor for the functional homogenization of fish fauna.

Amazon Forest; Conservation; Ecomorphology; Functional diversity; Habitat use

Variables	Codes	Mean ± standard deviation	Explanation
LANDSCAPE SCALE:
Forest cover in the watershed (proportion)	FO	0.40 ± 0.33	Proportion of forest cover for each watershed based on Landsat images (30 x 30 m resolution, available at www.dgi.inpe.br/CDSR/). The forest cover was classified according to the supervised classification method (Jensen, 2000) in the software ERDAS 9.2.
Local scale: calculated from (at least 20 m) measurements obtained in each stream reach
Grasses in the stream banks (%)	GRA	35.02 ± 38.00	Percentage of the reach bank extension that was covered by marginal grasses derived from surrounding pasture entering the water. For this calculation, both stream sides were computed.
Submerged roots in the stream banks (%)	ROO	3.43 ± 5.87	Percentage of the reach bank extension that presented roots derived from riparian trees entering the water. For this calculation, both stream sides were computed.
Consolidate substrate (%)	CSU	2.11 ± 3.68	Percentage of gravel and cobbles (particles with 2-256 mm in size) on the bottom of each stream reach (following the classification of Krumbein & Sloss, 1963).
Large wood debris on the stream bed (%)	LWD	11.35 ± 10.77	Percentage of fallen branches and trees, representing large wood debris, on the stream bed of each reach.
Depth (cm)	DEP	27.26 ± 14.03	Average value of depth.

Traits	Codes	Calculation	Ecological significance
Relative depth	RD	Maximum height of the body divided by standard length.	Lower values indicate fishes inhabiting fast waters. It is directly related to the ability to perform vertical spins (Gatz, 1979).
Index of ventral flattening	IVF	Middle line height divided by maximum body height.	Low values indicate fishes inhabiting environments with high hydrodynamism, able to maintain their position even when stationary (Hora, 1930).
Relative area of pectoral fin	APF	Pectoral fin area divided by body area.	High values indicate slow swimmers, which use pectoral fins to perform maneuvers and breakings, or fish inhabiting fast waters, which use them as airfoils to deflect the water current upwards and thereby, maintain themselves firmly attached to the substrate (Mahon, 1984; Watson & Balon, 1984).
Pectoral fin aspect ratio	PFA	Maximum length of the pectoral fin divided by its maximum width.	High values indicate long fins, typical of fish that swim long distances (Watson & Balon, 1984), or pelagic fish that swim constantly (Casatti & Castro, 2006).
Relative eye position	EP	Distance from the middle of the eye to the base of the head, divided by head height.	Position of eyes is related to vertical habitat preference (Gatz, 1979); high values indicate dorsally located eyes, typical of benthic fish (Mahon 1984; Watson & Balon, 1984).
Fineness ratio	FC	Standard length divided by the square root of the maximum height of body, multiplied by the maximum body width.	The influence of body shape on the ability to swim; values from 2 to 6 indicate low drag, the optimum ratio for swimming efficiency is 4.5 (Blake, 1983).

Variables	Coefficient	Standard coefficient	Variance inflation factor	Standard error	t	P
NRI (r²adj = 0.03, P = 0.586)
Landscape variable:
FO	-0.003	-0.003	1.535	0.118	-0.023	0.982
Local variables:
GRA	0.199	0.244	1.803	0.128	1.551	0.126
ROO	0.094	0.115	1.188	0.104	0.902	0.370
CSU	0.069	0.084	1.052	0.098	0.700	0.486
LWD	0.055	0.067	1.104	0.100	0.545	0.587
DEP	0.058	0.071	1.058	0.098	0.588	0.558
NTI (r²adj = 0.51, P < 0.001)
Landscape variable:
FO	-0.631	-0.515	1.535	0.124	-5.074	<0.001
Local variables:
GRA	0.304	0.248	1.803	0.135	2.255	0.027
ROO	-0.140	-0.114	1.188	0.109	-1.276	0.206
CSU	0.059	0.048	1.052	0.103	0.572	0.569
LWD	0.127	0.104	1.104	0.105	1.202	0.234
DEP	-0.292	-0.239	1.058	0.103	-2.831	0.006

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Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Departamento de Biologia Animal e Vegetal, CCB, Universidade Estadual de Londrina, Rodovia Celso Garcia Cid, Km 380, Cidade Universitária, 86055-900, Londrina, Paraná, Brazil, Phone +55(43)3371-5151 - Londrina - PR - Brazil
E-mail: neoichth@nupelia.uem.br

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