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Orthoptera assemblages associated with macrophytes of floodplain lakes of the Paraná River

Abstract

Orthoptera assemblages associated with macrophytes of floodplain lakes of the Paraná River. The Orthoptera assemblage composition varies considerably, depending on habitat type. This study examines the spatiotemporal relationship between plant diversity, hydrometric level, environmental variables and the Orthoptera richness and abundance in floodplain lakes connected permanently or temporarily with the main channel of the Paraná River. The grasshoppers were collected fortnightly (April 2006May 2007). A total of 17 species were recorded and classified according to their frequency of occurrence in constant (7), accessory (4), or accidental (6) species. In the two lakes, the greater species richness and abundance was recorded in summer, thereby coinciding with the highest water level of the Paraná River. The most significant correlation between the orthopteran richness and abundance was with the water level. The aquatic plant richness was significantly different between the lakes, but the vegetation was dominated by Eichhornia crassipes (Mart.) Solms. (Liliales, Pontederiaceae). The lake, which was connected permanently, presented the highest values of diversity and abundance, proving to be a more diverse assemblage. The beta diversity was higher in the temporary connected lake than in the permanently connected one. The orthopterans assemblages were different between the lakes, Cornops aquaticum and Tucayaca gracilis were the species that contributed more to the level of dissimilarity. C. aquaticum was more representative in the lake temporarily connected, while T. gracilis in the permanent connected one. The water level of the Paraná River and the connectivity of the floodplain lakes play an important role to explain the abundance and richness of their orthopteran assemblages.

Acrididae; aquatic plants; diversity index; hydrological level; Insecta; Tettigonidae


BIOLOGY, ECOLOGY AND DIVERSITY

Orthoptera assemblages associated with macrophytes of floodplain lakes of the Paraná River

Soledad CapelloI,* * Corresponding author Associate Editor: Rodrigo F. Krüger ; Mercedes MarcheseI,II; María L. De WysieckiIII

IInstituto Nacional de Limnología (INALI-CONICET-UNL), Laboratorio de Vegetación, segundo piso. Ciudad Universitaria, Santa Fe (3000), Argentina. solecapello1@yahoo.com.ar

IIFacultad de Humanidades y Ciencias-UNL. Ciudad Universitaria, Paraje El Pozo, 3000 Santa Fe, Argentina. mmarchese@inali.unl.edu.ar

IIICentro de Estudios Parasitológicos y de Vectores (CEPAVE) (CCT-La Plata-CONICET-UNLP), Calle 2 nº 584, 1900 La Plata, Argentina. mlw@cepave.edu.ar

ABSTRACT

Orthoptera assemblages associated with macrophytes of floodplain lakes of the Paraná River. The Orthoptera assemblage composition varies considerably, depending on habitat type. This study examines the spatiotemporal relationship between plant diversity, hydrometric level, environmental variables and the Orthoptera richness and abundance in floodplain lakes connected permanently or temporarily with the main channel of the Paraná River. The grasshoppers were collected fortnightly (April 2006May 2007). A total of 17 species were recorded and classified according to their frequency of occurrence in constant (7), accessory (4), or accidental (6) species. In the two lakes, the greater species richness and abundance was recorded in summer, thereby coinciding with the highest water level of the Paraná River. The most significant correlation between the orthopteran richness and abundance was with the water level. The aquatic plant richness was significantly different between the lakes, but the vegetation was dominated by Eichhornia crassipes (Mart.) Solms. (Liliales, Pontederiaceae). The lake, which was connected permanently, presented the highest values of diversity and abundance, proving to be a more diverse assemblage. The beta diversity was higher in the temporary connected lake than in the permanently connected one. The orthopterans assemblages were different between the lakes, Cornops aquaticum and Tucayaca gracilis were the species that contributed more to the level of dissimilarity. C. aquaticum was more representative in the lake temporarily connected, while T. gracilis in the permanent connected one. The water level of the Paraná River and the connectivity of the floodplain lakes play an important role to explain the abundance and richness of their orthopteran assemblages.

Keywords: Acrididae; aquatic plants; diversity index; hydrological level; Insecta; Tettigonidae.

Composition of Orthoptera assemblages vary considerably, depending on habitat type (Kemp et al. 1990). Many biotic and abiotic variables influence orthopteran populations and assemblages: plant species composition (Strohecker et al. 1968; Kemp et al. 1990), vegetation structure (Clarke 1993), soil type (Pdaft 1984), temperature, radiation, humidity, food availability, oviposition sites, shelters from predators (Kemp et al. 1990), or biotic interactions such as predation or parasitism (Joern & Pruess 1986). Vegetation is one of the key factors that determine Orthoptera distribution and composition, as different species occupy specific habitats according to the food availability and their microhabitat thermal requirements (Fielding & Brusven 1992; Squitier & Capinera 2002).

In aquatic systems the habitat structure is often provided by macrophytes, and the significance of a habitat is demonstrated by a far greater abundance of macroinvertebrates than in water bodies without aquatic plants (Heck & Crowder 1991). The abundance and richness of the macroinvertebrate assemblages appears to be proportional to the density or biomass of the freshwater macrophytes (Crowder & Cooper 1982; Stoner & Lewis 1985). However, this relationship is less clear when referring to the structure type or shape rather than to the density of structural elements, because various macrophytes species tend to support different epiphytic communities (Rooke 1986; Chilton 1990; Humphries 1996).

The water-level fluctuations constitute the most important macrofactor that should be considered while explaining species richness, distribution, and abundance of organisms in aquatic systems (Lewis et al. 1987; Junk & Piedade 1993; Casco et al. 2005; Thomaz et al. 2007). On the other hand, as pointed out by Neiff (1996), the number and type of species in different hydrological stages change, and only a few can bear both phases (flood and drought). Variations in the hydrological regime lead to substantial temporal biotic and abiotic changes. During the low water level, the floodplain aquatic habitats become more isolated from each other and are subjected to local driving forces. Flood events increase the connectivity and similarities among habitats, thus overriding local factors by regional scale drivers (Ward & Tockner 2001; Thomaz et al. 2007). Water-level fluctuations of distinct frequencies, magnitudes, and durations cause different physical and biotic impacts on habitats that are strongly associated with habitat connectivity (e.g. distance from the main river, topography), thereby creating a shifting mosaic state that is characterized by habitats at different successional stages (Amoros & Bornette 2002; Palijan et al. 2008).

The concept of connectivity originally referred to gene flow between subpopulations of a metapopulation (Merriam 1984). Connectivity is a relatively new concept in ecology and has only recently caught the attention of ecologists. Hydrological connectivity (sensu Amoros & Roux 1988) refers to the exchange of matter (including organisms) and energy via the aqueous medium between different units of the riverine landscape. Floodplain water bodies differing in connectivity with surface waters of the main channel exhibit different successional trajectories and contain different biotic communities.

Several general hypotheses have been proposed that explain the relationships between plant and herbivore species richness (Hawkins & Porter 2003; Haddad et al. 2009), with insect herbivore diversity often viewed as generally increasing in its relationship to higher plant species richness due to an increased resource diversity (Haddad et al. 2001, 2009). Although habitat associations with grasshoppers have been studied since the early 1900s (Vestal 1913), understanding patterns of species diversity remains a continuing challenge in grasshopper ecology (Torrusio et al. 2002; Joern 2005). Many studies have examined the relationships between grasshopper community composition and vegetation patterns in grassland ecosystems worldwide (Kemp et al. 1990; Fielding & Brusven 1993; Sanchez & de Wysiecki 1993; Torrusio et al. 2002; Joern 2005; Branson 2011), but the relationships between the Orthoptera and macrophytes in floodplain environments are scarcely known.

This study examines the spatiotemporal relationship between plant species diversity, hydrometric level and the diversity of Orthoptera in aquatic plant communities belonging to different floodplain lakes of the middle Paraná River. The primary objectives were to (1) determine the alpha diversity in two lakes with a different connectivity; (2) ascertain the species composition of the orthopterans associated to macrophytes and establish the dominant, accessory, or accidental species; (3) determine the beta diversity between the lakes with different connectivity to the main channel of the Paraná River.

MATERIAL AND METHODS

Study site. The floodplain of the Middle Paraná River is 600 km in length (Paoli et al. 2000), thereby providing a heterogeneous mosaic of aquatic environments. We selected lakes that differ in their degree of connectivity with the main channel, being lakes that were connected either permanently (LCPer) (31º38' 43.77"S; 60º34' 35.07"W) or temporarily to the Paraná River (LCTemp) (31º40' 14.40"S; 60º34' 44.43"W) (Fig. 1).


The vegetation of these floodplain lakes is directly associated with the hydrologic regime of the Paraná River, because the species richness varies according to the water level. The most important macrophytes in the Middle Paraná River are Eichhornia crassipes (Mart.) Solms., Paspalum repens (Elliott) Kunth, Salvinia sp. Seg., Pistia stratiotes L., Azolla sp. Lam., Ludwigia peploides (Kunth) P.H. Raven, Echinochloa sp. P. Beauv., and Polygonum sp. L. (Sabattini & Lallana 2007).

During the studied period, the hydrometric level of the Middle Paraná River presented a range of variation of 3.92 m. The lowest value (1.54 m) was recorded in September 2006, while the highest value (5.46 meters) was recorded in March 2007.

Data collection. The Orthoptera are usually not considered aquatic insects, but some of these species are linked to freshwater habitats mainly by a relation to an aquatic host plant. The orthopterans that cannot develop without aquatic plants, especially for egg laying and nymph development, are considered the primary inhabitants of freshwater biota (Amédégnato & Devriese 2008).

The grasshoppers were collected fortnightly in each of the floodplain lakes from April 2006 to May 2007. For each sampling moment, we had chosen similar days in relation to climatic conditions, avoiding the days with strong winds and rain, so that there would not be an underestimation of the results.

The collection of individuals was carried out from a boat, using an entomological nylon net (500 µm mesh) of 70 cm in diameter, 1 m in depth and the net handle length was 1.30 m. The sampling was carried out for a total period of 15 minutes sweeping on the aquatic plants. In order to know what plant species were dominant and while analyzing the possible variations of floristic composition between the lakes, the specific composition and vegetation of the macrophytes was analyzed by using the square method (70 x 70 cm). According to Foster et al. (1991), photo quadrates are more precise in estimating cover quadrates rather than point quadrates. For this reason, we obtained photographic records of each square. In each sampling, 10 photographs were randomly taken. The camera was maintained at a constant high during each photograph, and the photographic images were taken perpendicular to the substrate. These images were carefully analyzed by obtaining the proportion of each macrophyte.

All the captured Orthoptera were brought to the laboratory and preserved in the freezer for later and correct identification of taxonomic level by using different keys: Carbonell (1957, 2000), Carbonell et al. (2006), Montealegre-Zapata (1996), Roberts & Carbonell (1979), and Salto (1999).

Data analysis. Grasshoppers species richness and total abundance (total number of orthopterans/sampling) in each lake at each sampling moment were calculated. Species richness accumulated during the period studied (2006-2007) was obtained.

The Bodenheimer Index (Bodenheimer 1955) was applied for analyzing orthopteran species constants, using the following formula: c = p x 100/P, where p is the number of samples where the specie i is recorded, and P is the total number of samples. In relationship to the c value obtained, the orthopterans were classified in the following manner: Constant species: > 50%, Accessory species: between 25 and 50%, and Accidental species < 25%.

To establish which Orthoptera species contributes to observed differences in the data and to determine which species characterizes and discriminates each Orthoptera assemblage area, we used SIMPER (Similarity Percentage). This is a simple method of assessment in which taxa are primarily responsible for an observed difference between groups of samples, and it is based on the analysis of BrayCurtis similarity matrices that are derived from the species compositions between stations (Clarke 1993). The PRIMER v6 (Clarke & Gorley 2006) was used for this analysis.

In order to ascertain the relationship between species richness, abundance of orthopterans, climatic variables (temperature, mean temperature, minimum temperature, humidity, and precipitation), hydrometric level, and macrophytes species richness (expressed as special heterogeneity) were estimated using correlations. The statistical software XLSTAT 7.5.3 was used.

Orthopterans diversity was calculated as the ShannonWiener Index and Hulbert's PIE Index (Colwell 2005). Hulbert's PIE is the probability that two randomly sampled individuals from the same community pertain to two different species. It is an evenness index that combines the two mechanistic factors affecting diversity: dominance and species abundance. In addition, the dominance was also calculated. All these indexes were generated by a randomization process using EcoSim (Gotelli & Entsminger 2009).

The degree of distinctness among the lakes was measured using the complementarity index suggested by Colwell & Coddington (1994). The value of this index, expressed as a percentage, ranges from 0% for an identical species composition to 100% for an entirely different species composition. This measure of complementarity is, therefore, a direct measure of beta diversity. In addition, the rate of replacement of the species in each lake that was proposed by Whittaker (1972) was calculated. This index has proved to be more robust in measuring the replacement between communities (Wilson & Schmida 1984; Magurran 1989).

RESULTS

Orthoptera species richness and relative abundance of individuals. A total of 17 orthopteran species representing two suborders, four families, and ten subfamilies were recorded. The individuals were classified according to their frequency of occurrence in constant (seven), accessory (four), or accidental (six) species. The constant species are considered aquatic due to their relationship with the freshwater environment (Table I).

The grasshoppers richness accumulated was to 17 species in the LCPer, while in the LCTemp, the richness accumulated was to 15 species. The species richness was significantly different between sites (U de MannWhitney Z = 2,355; p = 0,019).

In the two floodplain lakes, the greater species richness was recorded in late summer (February and March 2007), coinciding with the highest water levels of the Middle Paraná River (Fig. 2).


A total of 5.236 individuals was collected throughout the study period sampled. The 60.30% (3.158 individuals) belong to the suborder Caelifera, while 39.70% (2.078 individuals) correspond of the suborder Ensifera.

The total abundance of Orthoptera in LCPer was greater (3.377 individuals), but there were no significant differences between the two lakes (p > 0.05). The higher abundance was obtained in summer, whereas the lower abundance was obtained in winter (Table II).

The data obtained in this study showed that species richness was different between the two lakes with a different connectivity (U de MannWhitney Z = 2.355; p = 0.019), but this did not happen in the same manner with the abundances. However, the results obtained by SIMPER showed that these species abundances vary between sites, resulting in a dissimilarity value of 51.30 (average dissimilarity) between the lakes. The species that had major differences in the contribution for the total assemblage of Orthoptera in each lake were Cornops aquaticum Bruner, 1906 and Tucayaca gracilis (Giglio-Tos, 1897). In the first case, the LCPer recorded a 21.29% contribution toward increasing this value in the LCTemp (46.02%). In opposition, T. gracilis had a greater contribution in the LCTemp than in the LCPer (20.23% and 4.18%, respectively). Thus, the orthopterans assemblage of LCPerm was characterized by Phlugis sp. Stål, 1861, C. aquaticum, T. gracilis, Gryllidae, Paulinia acuminata (De Geer, 1773) and Scudderia sp. Stål, 1873 whereas in LCTemp by C. aquaticum, Phlugis sp., Gryllidae, Scudderia sp. and T. gracilis in abundance decrease (Fig. 3).


The correlation between the richness and abundance obtained with the hydrometric level and the precipitations was significant (p < 0.001). The correlation between the vegetal cover (measured as water hyacinth proportion) and the habitat heterogeneity (measured as the plant species) was not significant (p > 0.05) (Table III).

Macrophyte cover. The accumulative species richness of the macrophytes was low, with a total of 20 species detected across sites (Table IV). The vegetation was dominated by Eichhornia crassipes (Mart.) Solms, and this macrophyte was a unique aquatic plant registered in all the samples.

The plant richness was significantly different between the two lakes (U de MannWhitney Z = -1.984; p = 0.047), as well as the proportion of E. crassipes between the environments (U de MannWhitney Z = -3.628; p < 0.0001).

In the LCTemp, the species richness of the macrophytes was positively correlated with the hydrometric level of the river (r = 0.630; p = 0.003) and with the species richness of Orthoptera (r = 0.448; p = 0.048). In contrast to this, in the LCPer, there were no significant correlations between these variables.

On the other hand, the correlations between plant richness and Orthoptera abundance were not significant (p > 0.05) in the two lakes with a different connectivity (Table III).

Diversity indexes. The LCPer presented the highest values of the Shannon-Wiener Index (1.96), Hulbert's PIE Index (0.81), and the lowest dominance (0.35), proving to be a more diverse assemblage. The values recorded for the LCTemp were 1.59, 0.71, and 0.46, respectively. The species richness and diversity was higher in summer in both the lakes, with the permanently connected lake showing more variation in the values (Fig. 4).


Diversity beta between the floodplain lakes (spatial diversity), according to the complementarily index, was 0.12. This means that both lakes have a similar composition of species, and only 11.7% of the species of Orthoptera are complementary between environments.

The results obtained from the Whittaker Index in each lake, that is, the replacement of species throughout the year, showed that LCTemp presented a higher turnover (1.73) than LCPer (1.19).

DISCUSSION

The results of this study allowed an analysis of the simultaneous and comparative Orthoptera assemblages between floodplain lakes permanently and temporarily connected to the Paraná River. The species richness in the Orthoptera is determined by a complex relationship between external factors, such as the climate and vegetation, and internal factors, such as population dynamics (Joern 2005; Zhong-Wei et al. 2006).

Based on the results obtained, only seven of the 17 Orthoptera species found associated to the water hyacinth can be considered constant species of aquatic habitats. Three of them are Acrididae: Paulinia acuminata, Cornops aquaticum and Tucayaca gracilis. The first two species have been widely studied for their use as potential agents of biological control of weeds: Salvinia auriculata Aubl., 1775 (Thomas 1980; Sands & Kassulke 1986; Vieira & Adis 1992) and Eichhornia crassipes (Bennett & Zwölfer 1969; Silveira-Guido & Perkins 1975; Hill & Oberholzer 2000; Oberholzer & Hill 2001; Adis & Junk 2003), respectively. On the other hand, the three species of Ensifera that were registered were described as the insects that inhabit moist places and those near to the water: Phlugis sp., Conocephalus sp., and Scudderia sp. The crickets collected in this study were cited by other authors as being a part of the insect community living on floating aquatic plants (Carbonell 1980; Albertoni et al. 2007).

The number of recorded orthopterans associated to the aquatic plants with adaptive strategies to live in wet environments were 13 species (Acrididae and Romaleidae), whereas Carbonell et al. (2006) reported a higher species richness (75 acridids) including terrestrial habitats. C. aquaticum and P. acuminata have been considered the most aquatic species according to Bentos-Pereira & Lorier (1991). In agreement, we classified the same acridids as constants in the macrophytes in the floodplain lakes studied. In addition, Bentos-Pereira & Lorier (1991) mentioned that T. gracilis is a species that frequently occurs in aquatic environments; but in our study, this grasshopper has attained great abundance while being placed within the constant species found on the aquatic vegetation.

On the other hand, Marellia remipes Uvarov, 1929, well adapted to the freshwater environments (Uvarov 1929, 1930; Carbonell 1957; Bentos-Pereira & Lorier 1991), was registered in low abundance, with 30 individuals captured during the study period. This result may be explained, because these acridids are related to Hydrocleis nymphoides (Humb. & Bonpl. ex Willd.) Buchenau (Butomaceae), an aquatic plant growing in quiet and clean waters (Carbonell & Arrillaga 1958), which was observed only occasionally owing to the suspended sediments load, the exposition of the wind, and the hydrologic dynamics of the lakes studied.

The species richness of insect herbivores is positively correlated with the area covered by their host plants (Strong et al. 1984), and it is independent of the habitat heterogeneity (Grez 1992). However, we did not find the same relation with the plants richness in the floodplain lakes studied. Thus, a significant correlation between habitat heterogeneity (plants richness) and species richness of orthopterans was obtained in the temporary connected lake (LCTemp), whereas no significant correlation was observed in the permanently connected lake (LCPer). Therefore, the connectivity between the floodplain lakes and the channels plays an important role in the orthopteran richness associated to aquatic plants. In addition, the water level of the river was the variable that was considered more important in the grasshopper abundance and species richness variation, attaining the highest values along with the maximum water level. By coincidence, the hydrologic effect was reported by Nunes & Adis (1992), Nunes et al. (2005), Vieira & Adis (1992), for others Orthoptera in central Amazonia, at the alluvial plain of the Amazonas-Solimões River. Thus, P. acuminata presented more abundance of nymphs and adults in high water than low water (Vieira & Adis 1992). On the other hand, the water level had an indirect effect on the populations of Phlugis teres (De Geer, 1773), because the macrophyte abundance was regulated (Nunes et al. 2005).

The macrophyte composition and abundance in floodplain lakes is largely determined by the water level regime (Junk 1970; Junk & Piedade 1993, 1997; Neiff 1979, 1990a, 1990b, 1999; Neiff et al. 2001; Piedade & Junk 2000; Parolin et al. 2004; Thomaz et al. 2004). In addition, the macrophyte represents the habitat and trophic resources for herbivorous insects, the aquatic plant communities are the support for aquatic orthopteran assemblages, and their abundance and richness depends on the abundance and distribution of the vegetation.

Instead, the temporal variation of plant communities (biomass, structure and diversity) in their relationships with drought or floods affects the distribution, density and composition of the orthopterans (Evans 1988; Kemp 1992a,b; Cigliano et al. 1995, 2000; Branson et al. 2006; Branson & Sword 2009).

The macrophyte composition showed significant differences between the floodplain lakes with a different connectivity with the main river. The highest species richness was attained in the permanently connected lake during the low water level, whereas the lowest species richness was obtained in the temporary connected lake. In addition, the hydrologic regime has a different effect on the aquatic plants richness in the lakes that are connected or disconnected with the river. By coincidence, Boschilia et al. (2008) showed that macrophyte assemblages are organized differently depending on the degree of connectivity.

The beta diversity was higher in temporary connected lakes than in the permanently connected ones, suggesting a greater change among the species of Orthoptera between different sampling dates. This phenomenon probably gives rise to the fact that this environment has more unstable hydrological conditions, thereby indirectly affecting the diversity of the grasshoppers and tettigonids present on the macrophytes.

In summary, our results show that the water level of the Paraná River and the connectivity of the floodplain lakes are the most important forces that should be considered to explain the abundance and richness of orthopteran assemblages. The floodplain lakes were characterized by different orthopteran assemblages, the richest ones found in the floodplain lakes with a permanent connection with the main channel. The effect of the high water level in increasing the abundance and species richness of orthopterans in the lakes may also be explained by the fact that semi-aquatic or terrestrial grasshoppers may use the macrophytes as food, shelter, and so on, during the floods.

ACKNOWLEDGEMENTS

We thank Language Edit for the revision of our manuscript. This work was funded by CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), Argentina.

Received 03 July 2012; accepted 13 November 2012

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  • *
    Corresponding author
    Associate Editor: Rodrigo F. Krüger
  • Publication Dates

    • Publication in this collection
      01 Apr 2013
    • Date of issue
      Mar 2013

    History

    • Received
      03 July 2012
    • Accepted
      13 Nov 2012
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