AIM: In order to understand the factors which influence the predatory activity of the Hoplias aff. malabaricus, the present study evaluated feeding habits of this species and its relation to prey availability, in addition to environmental variables. METHODS: Six samplings were conducted in the Taperoá II reservoir, semi-arid of Paraíba state, Brazil, between October 2005 and October 2006. Measures were taken: rainfall, the reservoir volume, transparency, dissolved oxygen, pH, temperature, nitrate, nitrite, ammonia and phosphate. The activity, diet and feeding habits of H. aff. Malabaricus, from the method of frequency of occurrence of food items and point methods, conjugates in IAI (Alimentary Index). Spearman correlation analysis, a glm and CCA were performed between biotic and abiotic variables, and we used the CPUE as a measure of fish abundance. RESULTS: Eleven taxa of fish were recorded, four of which were predated by adult "trahira". Insects and other items were also common in the stomachs of juveniles. According to statistical analysis, it was observed that the highest consumption of cichlids was correlated with its increase in CPUE in the environment, while no relationship was observed for A. bimaculatus, C. bimaculatum and S. notonota abundances. The environmental factors as nutrients, transparency and water volumn were related to selection of species by trahira. CONCLUSIONS: Intrinsic characteristics of preys as swimming speed, food habit and the food preference of the predator possibly be the main factors to selection of species. Other mechanisms as heterogeneity of habitat and environmental factors can also influence the consumption of prey by trahira
feeding; predation; reservoir; semiarid; fish
OBJETIVO: A fim de se compreenderem os fatores que influenciam a atividade predatória de H. aff. malabaricus, o presente trabalho avaliou o hábito alimentar e a sua relação com a abundância de suas principais presas e algumas variáveis ambientais. MÉTODOS: Realizaram-se seis amostragens no Açude Taperoá II, semi-árido paraibano, Nordeste do Brasil, de outubro de 2005 a outubro de 2006. Foram tomadas as medidas de: pluviosidade, volume do açude, transparência, oxigênio dissolvido, pH, temperatura, nitrato, nitrito, amônia e fosfato. Analisou-se a composição da ictiofauna, a atividade, dieta e hábito alimentar de H. aff. malabaricus, a partir do método de frequência de ocorrência dos itens alimentares consumidos e do métodos de pontos , conjugados no IAi (Índice de Importância Alimentar). Análises de correlação de Spearman, glm e CCA foram realizadas entre as variáveis bióticas e abióticas, e utilizou-se o CPUE como uma medida de abundância das espécies de peixes. RESULTADOS: Registraram-se 11 taxa de peixes, dos quais quatro foram presas da traíra adulta. Insetos e outros itens foram registrados nos estômagos dos juvenis. De acordo com as análises estatísticas, observou-se que o maior consumo de ciclídeos foi correlacionado com a sua abundância no ambiente, enquanto nenhuma relação foi observada para A. bimaculatus, C. bimaculatum e S. notonota. Fatores ambientais, como nutrientes, transparência e volume da água estiveram relacionados com a seletividade do consumo da traíra. CONCLUSÃO: Características intrínsecas como rapidez de locomoção, atividade alimentar da presa e a preferência alimentar do predador possivelmente sejam os principais fatores de seleção dos recursos consumidos. Outros mecanismos como a heterogeneidade de habitat e fatores ambientais podem também influenciar o consumo de presas pela traíra
alimentação; predação; reservatório; semi-árido; peixe
Piscivory by Hoplias aff. malabaricus (Bloch, 1794): a question of prey availability?
Piscivoria por Hoplias aff. malabaricus (Bloch, 1794): uma questão de disponibilidade de presas?
Ana Karla Araujo MontenegroI; Ana Carolina Brito VieiraI; Maria Marcolina Lima CardosoII; Jane Enisa Ribeiro Torelli de SouzaI; Maria Cristina CrispimI
ILaboratório de Ecologia Aquática LABECO, Departamento de Sistemática e Ecologia, Universidade Federal da Paraíba UFPB, Cidade Universitária, Campus I, CEP 58059-900, João Pessoa, PB, Brazil e-mail: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org; email@example.com
IIPós-graduação em Ecologia PGE, Universidade Federal do Rio Grande do Norte UFRN, Av. Sen. Salgado Filho, 3000, Lagoa Nova, CEP 59078-970, Natal, RN, Brazil e-mail: firstname.lastname@example.org
AIM: In order to understand the factors which influence the predatory activity of the Hoplias aff. malabaricus, the present study evaluated feeding habits of this species and its relation to prey availability, in addition to environmental variables.
METHODS: Six samplings were conducted in the Taperoá II reservoir, semi-arid of Paraíba state, Brazil, between October 2005 and October 2006. Measures were taken: rainfall, the reservoir volume, transparency, dissolved oxygen, pH, temperature, nitrate, nitrite, ammonia and phosphate. The activity, diet and feeding habits of H. aff. Malabaricus, from the method of frequency of occurrence of food items and point methods, conjugates in IAI (Alimentary Index). Spearman correlation analysis, a glm and CCA were performed between biotic and abiotic variables, and we used the CPUE as a measure of fish abundance.
RESULTS: Eleven taxa of fish were recorded, four of which were predated by adult "trahira". Insects and other items were also common in the stomachs of juveniles. According to statistical analysis, it was observed that the highest consumption of cichlids was correlated with its increase in CPUE in the environment, while no relationship was observed for A. bimaculatus, C. bimaculatum and S. notonota abundances. The environmental factors as nutrients, transparency and water volumn were related to selection of species by trahira.
CONCLUSIONS: Intrinsic characteristics of preys as swimming speed, food habit and the food preference of the predator possibly be the main factors to selection of species. Other mechanisms as heterogeneity of habitat and environmental factors can also influence the consumption of prey by trahira.
Keywords: feeding, predation, reservoir, semiarid, fish.
OBJETIVO: A fim de se compreenderem os fatores que influenciam a atividade predatória de H. aff. malabaricus, o presente trabalho avaliou o hábito alimentar e a sua relação com a abundância de suas principais presas e algumas variáveis ambientais.
MÉTODOS: Realizaram-se seis amostragens no Açude Taperoá II, semi-árido paraibano, Nordeste do Brasil, de outubro de 2005 a outubro de 2006. Foram tomadas as medidas de: pluviosidade, volume do açude, transparência, oxigênio dissolvido, pH, temperatura, nitrato, nitrito, amônia e fosfato. Analisou-se a composição da ictiofauna, a atividade, dieta e hábito alimentar de H. aff. malabaricus, a partir do método de frequência de ocorrência dos itens alimentares consumidos e do métodos de pontos , conjugados no IAi (Índice de Importância Alimentar). Análises de correlação de Spearman, glm e CCA foram realizadas entre as variáveis bióticas e abióticas, e utilizou-se o CPUE como uma medida de abundância das espécies de peixes.
RESULTADOS: Registraram-se 11 taxa de peixes, dos quais quatro foram presas da traíra adulta. Insetos e outros itens foram registrados nos estômagos dos juvenis. De acordo com as análises estatísticas, observou-se que o maior consumo de ciclídeos foi correlacionado com a sua abundância no ambiente, enquanto nenhuma relação foi observada para A. bimaculatus, C. bimaculatum e S. notonota. Fatores ambientais, como nutrientes, transparência e volume da água estiveram relacionados com a seletividade do consumo da traíra.
CONCLUSÃO: Características intrínsecas como rapidez de locomoção, atividade alimentar da presa e a preferência alimentar do predador possivelmente sejam os principais fatores de seleção dos recursos consumidos. Outros mecanismos como a heterogeneidade de habitat e fatores ambientais podem também influenciar o consumo de presas pela traíra.
Palavras-chave: alimentação, predação, reservatório, semi-árido, peixe.
Predation is one of the most important factors controlling the structure and abundance of fish communities in freshwater environments. Understanding the mechanisms responsible for predator-prey interactions is amongst the most important means of determining patterns of population dynamics (Piana et al., 2006). Piscivorous fishes have a profound direct or indirect effect on the overall community and on water quality, given their top positions on trophic webs and the underlying regulation of prey population sizes (Nowlin et al., 2006). Several studies investigated the role of predation on population dynamics (e.g. Novakowski et al., 2007). Some of the well known positive effects of predation come about from the selective pressure directed to weaker prey individuals, and the control of dominant species, therefore maintaining appropriate levels of diversity (Popova, 1978). However, negative effects, mostly due to intense predatory activities affecting the dynamics and abundance of prey species, have also been reported (Wootton, 1990).
Amongst the most important piscivorous fishes of freshwater environments in Brazil, the "trahira" (Hoplias aff. malabaricus Bloch, 1794) is a sedentary, opportunistic predator and tolerating several habitats, from open to macrophyte-dominated areas (Milani et al., 2010, Petry et al., 2010). This species has a broad geographic span in the Neotropical region, being virtually present at every hydrographic basin of Brazil, and with at least seven documented subspecies (Petry et al., 2010).
Several studies on the biology and importance of the "trahira" to the dynamics of Brazilian environments have been conducted, particularly, in the Rio Paraná Basin (Petry et al., 2010; Novakowski et al., 2007; Luz-Agostinho et al., 2008; Peretti and Andrian, 2004), Amazonas (Galacatos et al., 2004) and Pantanal (Milani et al., 2010; Brandão-Gonçalves et al., 2010). Further, experimental studies on its feeding biology and its role on trophic cascades have also been documented (Botham et al., 2005; Botham and Krause 2005; Piana et al., 2006). Nevertheless, compared to these areas, semi-arid regions have received little scientific attention and data on the feeding biology of "trahiras" remain scant.
Along with biological interactions, several abiotic factors influence community dynamics, namely, temperature conditions, water quality and hydrological regimes. Although the semi-arid is amongst the most atypical biomes in the world, its intrinsic mechanisms of ecosystem function remain poorly understood, particularly when compared to other biomes (Humphries and Baldwin, 2003).
In semi-arid regions, the low and irregular pluviometric rates, as well as intense evaporation caused high fluctuations in water level and seasonal changes in water quality (Pérez-Martínez et al., 1991), and led to adaptations of morphological, physiological and behavioral nature to harsh conditions (Cowx et al., 1984; Wilhite, 2000).
Because, the hydrological cycles can adds complexity to the predator-prey relationship and studies of the dynamics of piscivorous fish their prey are absent in aquatic semi-arid regions, we aimed to test the following hypothesis: a) as Hoplias aff. Malabaricus is a sedentary predator, its diet is related to prey availability; b) the environmental factors play an important role in prey capture by H. aff. malabaricus.
Encouragement of the present study were threefold, namely, the scarcity of studies conducted in the study region, the ecological role played by the subject species on freshwater environments and its economical importance as animal protein for local human populations.
2. Material and Methods
2.1. Study site
Taperoá II reservoir is located at the Taperoá River basin, in the central region of Paraíba State (07 11' 44" S to 07Âº 13' 44" S and 36Âº 52' 03" W to 36Âº 50' 09" W) (Figure 1). It has a surface area of 4.6 Km2, maximum water capacity of 15,148,900 m3, maximum depth of 5.7 m and mean depth of 1.4 m. The reservoir supplies water to Taperoá city and, during periodic events of overflow, to neighboring cities nearby the intermittent Taperoá River.
The semi-arid region of Paraíba has two well-defined seasons, namely, the rainy season, lasting between three and four months, and the dry season, lasting between eight and nine months. The weather at this region is classified as BSh' (Köppen climate classification), indicating a hot and dry semi-arid climate, with a rainy season lasting throughout the summer and fall. This region has the lowest precipitation indexes of Brazil (i.e. 300 mm per year).
Sampling was carried out during the 2005 dry season (October and December), 2006 rainy season (March and June), and 2006 dry season (August and October). Pluviometric and water volume data were provided by Agência Executiva de Gestão das Águas do Estado da Paraíba (AESA, 2007) (Figure 2).
Weather during the study period encompassed three distinct seasons, namely, a dry season between October 2005 and January 2006, a rainy season between February and June 2006 and another dry season between July and October 2006. The highest pluviometric rate (353 mm) was recorded in March, a somewhat atypical level for the region. Water volume in the Taperoá II reservoir showed high fluctuations throughout the study period, varying between 3.930.838 m3 in December 2005 and 15.148.900 m3 in May, June and July 2006 (overflow).
However, contrary to what was observed at preceding years (1998 and 2003), the reservoir did not dry completely during the study period (Figure 2). Multi-species macrophyte banks (Eichhornia crassipes, Salvinia sp., Egeria densa and Cyperaceae) predominated during periods of high water volume.
2.2 Sampling procedures
Six samplings were performed during a 24 hours period, where samples were collected in the deepest sector of the reservoir on the limnetic and shore zones, at four hours intervals, totaling six samples per sampling day. Fish specimens were collected using the following fishing instruments: cast nets and seine nets (15 mm mesh net between adjacent knots, nylon bags with 0.2 mm of net opening; length and width of 5 and 2 m, respectively), and gillnets (meshes of 15, 20, 25, 35 and 40 mm, between adjacent knots; length and height of 20 and 2 m, respectively). During each interval gillnets and cast nets were used in the reservoir edges, 30 and 15 times, respectively, whereas the seine net was used 10 times, in the edges and in the limnetic zone of the reservoir.
Abiotic variables were estimated in field or analyzed at the Aquatic Ecology Laboratory, Departamento de Sistemática e Ecologia, Universidade Federal da Paraíba from collected water samples. These variables included: water temperature (Inconterm mercury thermometer; 0.1 ÂºC precision), pH (Handlab portable pHmeter), water transparency (Secchi disk), dissolved oxygen (Winkler's method modified according to Golterman et al. (1978), ammonia (phenol method), nitrite (colorimetric method), nitrate (cadmium reduction method), orthophosphate (ascorbic acid method) and total phosphorous (persulphate) (Eaton et al., 1998).
2.3. Biological evaluations
Assessment of prey availability in the reservoir was conducted evaluating fish composition during the study period. In field, the collected specimens were preserved on a 10% formalin solution and subsequently transferred to the Laboratory. Taxonomic identifications followed Fowler (1954), Britiski (1972), Britiski et al. (1984) and Vari (1991), and were confirmed by a taxonomist (Dr. Ricardo S. Rosa). Voucher specimens were deposited at the Ichthyologic Collection of Universidade Federal da Paraíba (UFPB catalogue numbers: 6175, 6176, 6177, 6178, 6179, 6180, 6181, 6182, 6183, 6184 and 6185).
As a measure of fish abundance, we used the catch per unit effort of fishing (nÂº individuals/m2 of net/hour or nÂº individuals/m2 net/throw) using the mean of catches in data analysis. To determine population size structure, specimens were measured (standard length), being classified as adults or juveniles by the observation of the maturation stage of gonads.
Stomachs removed from 59 collected individuals were instantly fixed using a 10% formalin solution in field and subsequently (in lab) preserved in a 75% alcohol solution. Feeding activity was determined based on stomach repletion degree, classified according to Hahn et al. (1997). Its contents were analyzed as a means to determine the diet and feeding habits of the species. Feeding items were identified to the lowest possible taxonomic level based on specialized literature and with the aid of taxonomic specialists. Diet was determined based on the frequency of occurrence of feeding items consumed (Zavala-Camin, 1996) and from the points method (Hynes 1950; Fugi et al., 1996).
Importance of feeding items in the diet of the collected individuals was determined based on the Alimentary Index (IAi) (Kawakami and Vazzoler 1980), calculated by combining values from the frequency of occurrence and points methods.
The selectivity index of J. Chesson (1978a) was used to compare the items consumed by H. aff. malabaricus, considering its availability in the environment (Equation 1):
When αi < 1/n, a negative selection occur. When αi > 1/n, indicate a positive selection, and when α = 1/n, selective feeding does not occur. Because n = 11 here, then 1/n = 0.09. We choose this index because has been widely used for can to incorporate easily in biological models and unlike other models can be applied to more than two preys, and consider constant and non-constant preys (Chesson, 1978a).
2.4. Data analysis
A Pearson Correlation Test was performed to relate the selectivity of the predator and abundance of prey in the environment. Before of Canonical Correspondence Analysis, a stepwise generalized linear regression with backward selection was used to understand the extent to which the measured biological and environmental variables (precipitation, water volume, transparency, nitrite, nitrate, ammonia, phosphate, and prey abundance) explained patterns of predation by H. aff. malabaricus. The CCA tested how the environment variables influenced the selectivity index. Significance of the first two axes was tested using a permutation test (10000 interactions). Before CCA the data were standardized by dividing each value of one variable by its sum of the raw and multiplying by 100. All analyses were conducted using R software (R Development Core Team, 2007).
According to the analysis of environmental variables, observed values summarized in Table 1.
Within fish composition, a total of 889 individuals from eleven taxa, ten genera, nine families and four orders were identified in environment. Temporal variations in species abundance were detected. Particularly, fewer individuals were collected during the rainy season (78 and 109 specimens during March and June of 2006, respectively) (Table 2).
Size (standard length) of the 59 H. aff. malabaricus individuals collected varied between 2.0 and 34.2 cm, with a 32.2 cm amplitude (mode: 22.9 cm). Individuals varying between 19.0 and 25.0 cm, categorized as adults, were the most frequent throughout the study period. During the 2005 dry season (August and October), both juveniles and adults were collected. Higher abundance of this species coincided with periods of low water volume in the reservoir (dry season of 2005).
Diet consisted of 19 items, 52.63% of which were recorded during the 2005 dry season, 57.89% during the 2006 rainy season and 36.84% during the 2006 dry season (Table 3). Fish represent the main item in the diet of H. aff. malabaricus (fish remains, IAi = 51.44%), from 2005 to the 2006 rainy season, confirming the piscivorous habits of adults of this species, given that 83.05% of the collected individuals were adults. In fact, benthic invertebrates, mostly Melanoides tuberculata (Müller, 1774), IAi = 21.76% during the 2006 rainy season; and insect remains, IAi = 18.58% during the 2006 dry season; largely contributed to diet of this species, particularly, for small individuals (i.e. juveniles).
Species which made up the diet of 49 H. aff. malabaricus adult individuals were Characidium bimaculatum (Fowler, 1941), Astyanax bimaculatus (Linnaeus, 1758), Steindachnerina notonota (Miranda Ribeiro, 1937), Synbranchus marmoratus (Bloch, 1795) and Cichlidae - Oreochromis niloticus (Linnaeus, 1758) and Cichlassoma orientale (Kullander, 1983), identified from fish remains (Table 3). A somewhat restricted diet was recorded during the 2005 dry season. S. marmoratus was not collected in the environment, but recorded solely from stomach content analyses. Although higher prey diversity was recorded during and after the 2006 rainy season, total abundance of prey was higher during dry seasons. Evidence of cannibalism was not observed.
For statistical analyses, only prey species recorded in stomach content analyses were included. Cichlids were the main alimentary item in three of six samples (Table 4), despite its low abundance in the environment. Among the consumed items, A. bimaculatus, C. bimaculatum, and S. notonota, despite their high abundance in the environment, registered low preference by the trahira (Table 4). Other species, such as A. fasciatus, e L. piau, and P. vivipara, presented great abundance in the environment, but were not consumed. The results of selectivity index confirm the preference by cichlids. The correlation test shows a significant correlation between the selection of cichlids with increase in abundance of these prey species (cor.test = 1; p < 0.001; Table 4). The consumption over other species was not related to its abundance in the environment.
A stepwise multiple regression has shown that cyclid consumption was associated to an increasing in transparency, nitrite and ammonia and water volume (Table 5). The variables with interference on the selection of S. notonota and A. bimaculatus were ammonia (negative relationship) and phosphorus (positive relationship) (Table 5), and nitrite, phosphorus and ammonia were negatively related to C. bimaculatum (Table 5).
By linking the selectivity index with environmental variables in a CCA, the first axis explained 54.5% of the variance and axis 2 explained 36.2%. The explanatory factor 1 axis is the volume of the reservoir (0.51) and ammonia (0.48). Axis 2 was explained by phosphorus (0.88) and nitrite (0.41). CCA indicated that cichlids over the selectivity index was related to increased volume of the reservoir (-0.27) and C. bimaculatum was negatively correlated with the volume (0.22), the selectivity of A. bimaculatus was more related to the second axis (0.24) (Figure 3).
The permutation test showed that axis 1 correlations were significant (df = 1; F = 12.349; p = 0.02) and that axis 2 correlations were marginally significant (df = 1; F = 9.1955; p = 0.055).
We observed a higher proportion of fishes in the diet of H. aff. malabaricus, as indicated by previous studies (Hahn et al. 2004; Loureiro and Hahn, 1996). Furthermore, our results showed that H. aff. malabaricus select only a fraction of the available prey fishes and its diet did not entirely correspond to fish composition observed at the Taperoá II reservoir, suggesting that this species selectively captures its prey regardless of the abundance of all potential fishes in the environment. Other studies also suggested that diet is not necessarily an effect of prey availability in the environment (e.g. P. L. Chesson, 1978b) and assign it to a randomness in diet selection by the sedentary habit of trahira and environmental conditions as changes turbidity (as indirect factor of nutrient input) and water volume, as well as atypical predatory behaviors triggered by population increases of particular prey species, also play important roles in determining diet (Turesson, 2003; Vucic-Pestic et al., 2010). With the exception of March 2006, during which IAi values corresponded to fish composition at the reservoir, inconsistency between potential prey (fish composition) and diet (stomach contents) were always observed.
Factors such as habitat preference, environmental conditions, prey size and mobility can play a major role on selectivity than prey abundance (Luz-Agostinho et al., 2008; Milani et al., 2010). H. aff. malabaricus is an ambush predator, selectively occupying sites with high structural complexity, such as macrophyte banks, where prey abundance tends to be high, thus increasing success of prey capture (Luz-Agostinho et al., 2008), as observed in the present study during the 2006 rainy season. Aquatic macrophytes play an important role in lowland lakes by increasing microhabitat heterogeneity and, consequently, resources for prey (i.e. food and refuge), therefore reducing predator efficiency (Agostinho et al., 2007). With a decrease in microhabitat diversity, as observed during periods of low water volume in the reservoir (e.g. the 2005 dry season), predation becomes a laborious activity, given the reduced number of foraging sites. This pattern is supported by the low IAi values (prey ingestion) in dry seasons in the present study.
Although we had indentified 11 species in Taperoá reservoir, only four species were consumed by trahira: C. bimaculatum, S. notonota, A. bimaculatus and O. niloticus. The predation pressure towards C. bimaculatum individuals was higher during dry seasons. This was probably due to lower water volumes constraining the availability of macrophyte banks (i.e. refuge sites), therefore exposing individuals of this species. Characids are small-sized fishes with short life-cycles, typically abundant along margins of lakes and in association to macrophyte banks (Smith and Barrella, 2000).
The feeding on S. notonota seems to be at random, once it occurred in only one month, and the selectivity index indicated no preference by this item, despite its abundance in the environment. S. notonota is a small-bodied species (maximum length 10.7 cm), and despite trahira also eats small preys, its absence of selection over this one is probably related to its alimentary habits, for it is a detritivorous species, and inhabits preferentially deep areas (Montenegro et al., 2012).
Predation towards A. bimaculatus individuals corresponded to diminishment of the volume of the reservoir, and to the increasing in phosphorus concentrations, and the increasing in transparency as well, probably due to the low shelter and food availability in macrophyte beds, increasing the predation risk of A. bimaculatus. Also, although A. fasciatus was also common at the reservoir, sharing similar trophic niche and body size to A. bimaculatus (Agostinho et al., 1997), the former species was not consumed. This is probably due to A. bimaculatus being more abundant along margins of lakes, thus, corresponding to foraging sites of "trahiras". This was observed in the present study and also by Arcifa et al. (1991) in a eutrophic reservoir at the south region of Brazil. Furthermore, factors such as prey-detection (sight) and swimming performance may also be related to the mechanisms of prey selection by "trahiras".
Although the food selection did not occur over more abundant species in Taperoá reservoir, we identify a feed preference over cichlids. Cichlids were mostly consumed by "trahiras" during periods of higher water volume, particularly during the later rainy seasons, which corresponded to higher abundances of individuals of this group probably as a result of accidental escapes of small individuals of Oreochromis niloticus from nearby fish cages (personal communication from local fishermen). The alimentary habits of cichlids, being planktivores (Figueredo and Giani 2005) and occupying the water column, should be related to increased susceptibility to predation by trahira. In fact, predatory pressure is higher for cichlids than for other species and the increase in abundance of cichlids increases the consumption by trahira. The lower swimming speed and agility of cichlids than other species, as Astyanax bimaculatus and fasciatus (Novakowski et al., 2007) also can result in different vulnerability rates.
Although trahiras can eat large preys, they are known for their consumption on small prey because are gape-limited predators (Prejs, 1987; Loureiro and Hahn, 1996). Our results, support the idea of gape-limitation by trahiras, as the piscivorous consumed only small sized prey species in Taperoá reservoir.
In sum, our results do not support the hypothesis that Hoplias aff. malabaricus diet is related to prey availability, because the prey preference is seems to be the main factor to selection on prey Regardless of prey abundance, the trahira has a preference by cichlids and increased the consumption with increasing abundance of cichlids, although not represent the most abundant prey. We suggest that the intrinsic characteristics of the prey, such as size and agility play a central role in selection.
Also, we had evidences that environmental conditions can affect the consumption by semi-arid piscivorous, but are still deserve further experimental studies to identify how consumption rates change with increase in nutrients, transparency, and habitat heterogeneity. As native predators can decrease the competition among preys may favor a higher diversity of prey species (Kunte, 2007; Morin, 1981), factors that affect the rate of consumption of trahira can reduce the indirect benefic role of this piscivorous on prey communities. Also, the reduction in consumption rate by trahira can affect the degree of control over exotic species.
We thank PELD/Caatinga CNPq, for financially supporting the project and CAPES for providing a master degree grant to Ana Karla A. Montenegro.
Received: 02 August 2012
Accepted: 10 July 2013
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Publication in this collection
10 Sept 2013
Date of issue
02 Aug 2012
10 July 2013