Diversity and seasonal variations of in Sandspit (backwater) mangrove forest

Item Type article

Authors Nazim, Kanwal; Ahmed, Moinuddin; Ali, Qadeer Muhammad; Shaukat, Syed Shahid; Khan, Muhammad Uzair; Durrani, Agha Tahir Hussain; Ahmed, Quratulan; Zaheen, Wafra Matanat

Download date 02/10/2021 15:29:24

Link to Item http://hdl.handle.net/1834/40744 Pakistan Journal of Marine Sciences, Vol. 18(1&2), 61-66, 2009.

DIVERSITY AND SEASONAL VARIATIONS OF INSECTS IN SANDSPIT (BACKWATER) MANGROVE FOREST

Kanwal Nazim, Moinuddin Ahmed, Qadeer Muhammad Ali, Syed Shahid Shaukat, Muhammad Uzair Khan, Agha Tahir Hussain Durrani, Quratulan Ahmed and Wafra Matanat Zaheen Marine Reference Collection and Resource Centre, University of Karachi (KN, QMA, MUK, QA, WMZ); Laboratory of Dendrochronology and Plant Ecology, Department of Botany, Federal Urdu University of Arts, Science & Technology Karachi, Pakistan (MA, SSS); Sindh Forest Department, Karachi (ATHD). e-mail: [email protected]

ABSTRACT: The study deals with population diversity and seasonal variation of insects in Sandspit mangrove forest dominated by grey mangrove Avicennia marina. In order to examine the diversity and seasonal variations monthly data were collected from November, 2007 to October, 2008. A total of 26 species of insects were recorded, most of the species belonging to order Diptera. The highest diversity (H') 1.936 and richness (d1) 2.309 of insects were found in October while maximum value of evenness 1 was calculated in September. The highest value of dominance (D) 0.851 was recorded in March. The result indicates that physical structure of mangrove vegetation facilitates the habitation of fauna, canopy shade having an important function in providing cooler and wetter surface substrate at Sandspit area.

INTRODUCTION

Mangrove insects are diverse and abundant occupying number of niches, may be permanent residents of the mangle or only transient visitors.. The herbivorous insects feed on leaves, flowers, seeds or mangrove propagules which may cause considerable damage to the mangrove vegetation; the detritivorous eat dead wood or decaying leaves; more general foragers; and predators. However, some insects play vital role as pollinators and all in turn represent a major food source for predators. The mangrove insect fauna resembles that of terrestrial forests with many species in common to both. In mangrove forests of Pakistan the information regarding the significance of insects are scanty, although they play important ecological roles in the mangrove ecosystem. The present study focuses on current status of diversity of class Insecta at Sandspit (backwater) mangrove area which is an interesting addition to the knowledge of insect fauna in mangrove areas of Pakistan.

MATERIALS AND METHODS

The present research work was conducted during November 2007 to October; 2008. in Sandspit backwater mangrove forests (24°8490 N 66°.8947 E). The specimens were collected by placing insect sticky pad, imported from United States of America (Fig 1) and by sweeping net. The collected specimens were placed in glass/ plastic containers with Ethyl acetate and brought to the laboratory, sorted out, identified 62 Pakistan Journal of Marine Sciences, Vol. 18(1&2), 2009. and selected for detailed study. The specimens were finally preserved as a reference collection.

Fig. 1. Showing the insect trapper imported from U.S.A.

The abundance pattern and the number of species were calculated as proposed by famous Shannon and Wiener, (1963). This is obtained as follows,

th Where H′ is the general diversity and the pi is the proportions of individual of i species in the sample.

The species richness was determined by the index developed by Menhinick, (1964)

The equitability indices was measured by the following formula,

Concentration of dominance was measured in accordance with Simpson’s, (1949), Nazim at al: Seasonal variations of insects and arachnids in Sandspit 63

Where ni equals the number of individuals of ith species and N is the total number of individuals.

RESULTS

During present study a total of 26 species including., Cicendela histrio, Chrysochroa chinensis, Pericoma fuliginosa, febrilis, Holorusia sp., tessellata, Bibio marci, Calliphora vicina ,Anopheles sp., Culex fuscanus, Aedes sp. ,Apanteles glomeratus, Musca domestica, Nemopoda nitidula ,Ledra aurita, Aphrophora alni, Pycna repanda, Dactylopius tomentosus, Formica rufa, Apis mellifica, Apis mellifera, Vespidae sp. Pieris sp., Danaus plexippus, , Carduligaster baltonii and Acrotylus sp. belonging to eight orders were recorded. Diptera was the most dominant order consisting of 12 species (Fig. 2). Flowers and propagules also provides suitable habitat for some insects to lay their eggs.

Fig. 2. Number of species of insects in each order collected from Sandspit mangrove forest.

64 Pakistan Journal of Marine Sciences, Vol. 18(1&2), 2009.

Fig. 3. Total number of Insecta species collected during November 2007- October 2008

Large numbers of Diptera constitute diverse insect fauna in the mangrove forest. According to Hutching and Recher, (1974) dipterans specialize on the fruits and propagules of mangroves. Figure 4 showing the number of species of class Insecta collected from Sandspit. There is a variety of species including several beneficial insects (butterfly, wasps and honey bee) while many of them were harmful such as Fever , March fly, Black scavenger fly and mosquitoes. Apis mellifera collects nectar from Avicennia marina during flowering season (April to July). Four members of Hymenoptera viz. Formica rufa, Apis mellifera, Apis mellifica and a Vaspidae and one species of Lepidoptera Pieris sp. are commonly associated with mangroves; these were the seasonal visitors of mangrove forests, during the flowering season. Three species namely, Formica rufa, Culex fuscanus and Ledra aurita were found in highest number (Fig 4). The ants play an important ecological role according to Wilson, 1959 their high abundance and the multitude of interactions make them important part in ecosystem functioning. The highest number of ants were observed on the floor of the mangrove forests which have adapted to the daily tidal inundation by ploughing their burrows with mud and trapping bubble of air inside the burrow. Ellway (1974) stated that dead wood of mangrove provides suitable habitats for ants. Bengtson and Rupdgren, (1984) reported that ants among the , to be useful indicators of metal pollution, the number of species and densities of ants decreased with the increase of pollutant contamination. Two species of mosquitoes were also recorded in small and big water channels in Sandspit backwater which are ideal places for mosquitoes. Figure 4 showing the monthly variation in diversity, species richness, evenness and concentration of dominance of class insecta of phylum Arthropoda. The highest diversity (H') 1.936 and richness (d1) 2.309 of insect species was found in October while maximum value of evenness 1 was calculated in September. The highest value of dominance (D) 0.851 was recorded in March. This shows that the species diversity, Nazim at al: Seasonal variations of insects and arachnids in Sandspit 65 relative abundance, and population geometry vary with seasons because such variation affects the structure, stability, and energy flow through plant- communities, it must also affect the rate and perhaps the mode of speciation (Mac Arthur and Wilson, 1967). This statement clearly supported our results that Sandspit mangrove swamp has seasonally rich and diverse insect fauna. This may be due to the fact that Sandspit area is covered with thick mangroves, the canopy cover is very moist or wet due to proximity to the level of tidal water which favors insect’s activity and growth. According to Dindal et al., (1977) nevertheless both the species diversity and richness indices were increased considerably due to the complex effects of salts. Sandspit backwater receives pollution from Lyari river and other adjoining local population. According to Saifullah and Mehra, (2004) pollution also encourages the growth of the insects.

Fig. 4. Monthly variation in diversity, richness, equitability and dominance of insecta species in Sandspit mangrove forest

So, the present study provides interesting information to understand the diversity and seasonal variations of mangrove insects. Many species showed advanced forms of social behavior and play a vital role in processes such as predation, parasitism and pollination. This study will also help to understand the herbivory by plant feeding insects and the interactions among organisms.

REFERENCES

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Fransworth, E.J. and A.M. Ellison, 1991. Pattern of herbivory in Belizean mangrove swamps. Biotropica, 23:555-567. Hutching, P. A and H. F. Recher. 1974. The fauna of Careel Bay, with comments on Ecology of mangrove and sea grass communities. Australian Zoology, 99-128. MacArthur RH and EO Wilson, 1967. The theory of islandbiogeography. Prnceton University Press: Princeton. Menhinick, E.F. 1964. A comparison of some species individual’s diversity indices applied to sample of field insects. Ecology, 45: 859-861. Saifullah, S.M., S. Ismail, S.H. Khan and M. Saleem, 2004. Land Use- Iron pollution in a mangrove habitat of Karachi. Indus Delta. Earth Interactions, 8(17): 1-9. Shannon, C.E and W. Wiener, 1963. The Mathematical theory of communication. University of Illinois Press, Urbana. 117. Simpson, E.H. 1949. The measurement of diversity. Nature, 163:688 Wilson, E.O., 1959. Some ecological characteristics of ants in New Guinea rain forests. Ecology, 40:437–447.