Lake ecology
Dr.Asma Ali [Ecologist]
Dr.Asma Ali [Ecologist]
November 2019
Effect of predatory backswimmer on Dipteran communities
Effect of Predatory backswimmer N. maculata on community structure of Dipterans
Abstract :
Impact of predator N. maculata on distribution and abundance of Dipteran species Culiseta longiareolata, Tendipes tendipes and Tendipes kifferulus were investigated in an Urban Lake, Upper Lake Bhopal, India. The impact of invertebrate predation as observed in the present study (where the abundance of Notonecta maculata decreases, population of Dipteran species), has been documented for the first time in tropical waterbody, particularly in fresh water Lake. This work provides strong evidence that N. maculata is an important organizer of community structure and strongly reduces or even eliminates larger pelagic or neustonic species, but does not affect densities of small or benthic species.
Introduction :
The population abundance of aquatic insects are usually attributed on the basis of physico-chemical parameters of water bodies by many workers (Crosswell 1949, Mitchell 1959, Smith 1988, Singh 1995, Ravera 2001, Solimini et al. 2003, Arimoro et al. 2007). A second potential source of population abundance of aquatic insects has received less attention in density - dependence interactions between insects and their food competitors or natural enemies (Hutchins 1966, Andres & Cordero 1998, Yule 1996 and Gergs and Ratte ,2009). These early studies led to an explosion of experiment which documented the effect of aquatic insect Notonecta maculata on population abundance of dipteran community in tropical lake of India.
The importance of invertebrate predators in structuring communities has received less attention, but the growing number of prey-predators relationships show that they play an important role in aquatic ecosystem (Leucke & Litt 1987, Lounibos et al. 1987, Blaustein 1990, Blaustein & Ward 1995, Matveev 1995 and Andres & Cordero 1998). Notonecta maculata belongs to family Notonectidae is most common predator of aquatic system, have been shown to have a large impact on dipteran populations as well as other macrobenthic fauna (Scott & Murdoch 1983, Chesson 1984, Murdoch et al. 1984).
The potential role of predators in causing cascading frequently over the last decade (Kerfoot 1987; Bronmark et al. 1992, power 1992, Carpenter & Kitcheil 1993) by directly reducing primary consumer populations, predators such as N. maculata may indirectly cause an increase in algal Proliferation. There are no long term studies of the impact of N. Maculata predation in natural populations of dipterans in tropical lake. The objective of this study was to determine whether N. maculata reduce survival and population abundance of dipterans in waterbody.
N. maculata Fabricius (Hemiptera : Notonectidae) is a pelagic predator, feed on dipterans, that have been the subject of many laboratory studies to assess predatory habits and prey behaviour (Sih 1980, Giller & Mc Neill 1981, Scott and Murdoch 1983, Streams 1994, Sherratt and Mac Dougall 1995) outside the laboratory there is a less number of predatory behaviour of Notonectidae, in temperate lake (Ellis & Borden 1970, Hazelrigg 1974, Chesson 1989, Blaustein et al. 1995) although not a single prey- predator relationship in case of N. maculata has been recorded so far in tropical lake of India.
Description of the study area -
The Upper lake is located in Bhopal city, the capital of Madhya Pradesh, the largest state of India. This lake was created by constructing on earthen dam across the river Kolans in the 11th century. The Upper Lake has water spread area of 30.72 sq.km at FTL. The storage capacity is 101.6 million Cu.m, the maximum and mean depth being 11.7 and 6 m. respectively.
Outflow from the Upper Lake which receives water, mainly through the Kolans river drains into Kaliasot river and finds its way to Yamuna river though the Betwa river. The Kolans river feeding the Upper Lake, being a seasonal river flows for few days immediately after heavy rain. A waste weir at Bhadbhada controls overflow and thereby facilitate flood control.
Upper Lake is divided into perennial water, covered, marshy and submerged cum transitional zones. Due to the shallow nature of the last zone the lake becomes exposed from post monsoon period to summer season. Therefore the lake supports mainly 3 types of vegetation consisting of more than 100 terrestrial or marshy plant species and 34 aquatic species. The aquatic species have been categorised as floating forms (10 in number) submerged forms and emergent forms.
The lake is rich in biodiversity, principle components being aquatic vegetation includes 106 species of macrophytes, 208 phytoplankton species, 105 zooplankton species and 98 aquatic or shoreline insects.
The Upper Lake is under a massive conservation, restoration and management project funded by overseas Economic Cooperative Fund (OECF) Japan to protect it from environmental degradation not only due to its natural aesthetic value and rich biodiversity, but also since it is the main source of potable water. Selection of the sampling sites of the Upper Lake chiefly was done on the basis of weeds and consequent biomass sampling.
DISCUSSION :
N. maculata cause a large negative impact on C. longiareolata populations. We attribute the negative association between the predator and prey at all sampling stations of Upper Lake.
During the peak population of Notonecta there is a declining population of the Dipterans was observed, thus hemipterans stabilizing an inverse relationship with Dipterans. This inverse relationship can be explained in terms of prey and predator interactions as the hemipterans were found to feed on the dipterans, such as Tendipes tendipes, Tendipes kiefferulus, Culiseta longiareolata and Dolichocephala irrora and eliminated the population of dipteran species. Chesson (1984) found that a congener, Notonecta hoffmani, attacked and broke up Culex egg rafts and that Culex females oviposited less in the presence of Notonecta.
Thus it appears that apart from D.O. the abundance and sparse populations of the hemipterans as well as the dipterans may not be solely due to dissolved oxygen but is due to interdependent food webs suggesting a strong cascading trophic interaction.
With regard to the concept of predation, it is generally believed that higher aquatic communities such as fishes and Urodeles are known to be important organising factors of community structure.
It has been suggested that the efficiency of predators to reduce mosquitoes in Lake water may decline with increasing nutrients. The impact of Notonecta maculata on culiseta populations may not be as great in more nutrient rich sampling stations of Upper Lake, where larval densities may be higher and Dipteran development should be faster (Blaustein & Kottler 1993). Thus in a system with a higher nutrient base, the efficiency of Notonecta to control Culiseta populations may decrease due to faster mosquito development rates or higher densities of mosquitoes. Similarly Walde (1995) found that predatory mites impact on phytophagous mite populations were reduced when nutrient levels were increased.
Notonecta species are generally most efficient at preying on pelagic species and less effective at praying on species associated with vegetation such as Tendipes tendipes, T. kifferulus. Moreover, Giller & Mc Neill (1981) have shown that N. maculata is an efficient predator in open water rather than vegetative water. These mosquitoes, being associated with the vegetation, appear to be able to coexist with N. maculata.
We conclude that Notonecta has a very large impact on Culiseta populations, then other mosquitoes. i.e. T. tendipes, T. kifferulus and D. irrorata, often driving them locally extinct while other mosquito such as T. tendipes can coexist presumably because they occupy vegetation. Our results also suggest that backswimmer N. maculata can be important organising factor of community structure.
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