Available online at http://ajol.info/index.php/ijbcs Int. J. Biol. Chem. Sci. 3(6): 1320-1335, December 2009 ISSN 1991-8631 Original Paper http://indexmedicus.afro.who.int Influence of human activities on diversity and abundance of insects in Akure Forest Reserve, Ondo State, Nigeria Sunday Adeniyi ADEDUNTAN Forestry and Wood Technology Department, Federal University of Technology, Akure. P.M.B. 704 Akure. Nigeria. E-mail: [email protected], www.futa.edu.ng ABSTRACT This study was carried out to assess the impacts of human activities on insect diversity and abundance in Akure Forest Reserve, Nigeria. Three land uses (fallow land, cocoa agroforest and unlogged forest) were selected for field work within the forest reserve. An hectare block was centrally demarcated in each of the land use types where insects collection and enumeration of trees species took place. 13,578 insects distributed among 30 families belonging to 15 orders were collected and identified and preserved in the insect boxes in the Museum. Within the fallow land, a total of 5,182 insects belonging to 46 families and 8 orders were encountered, while in the cocoa agroforest, 5,884 insects distributed among 50 families and 10 orders and unlogged forest, consist of 2,490 insects distributed into 10 orders and 56 families. The families and order with the highest number of individual insects are Lepidoptera (4,000) and Orthopetera (1,260). These insects are mainly defoliators. The Shannon-weiner diversity index shows that unlogged forest is more diverse than the cocoa agroforest and fallow land. The tree species with the highest frequency per hectare is Cordia platythrsa (Boragiaceae) (6) in fallow land, Theobroma cacao (50) in cocoa agroforestry land Celtis zenkerii (Ulmaceae) in unlogged forest land. A total of 14, 26 and 41 species of tree were identified in the fallow land, cocoa agroforestry land and untouched forest respectively. © 2009 International Formulae Group. All rights reserved. Keywords: Biodiversity, agroforestry, insect defoliators, land uses, fallow land, conservation. INTRODUCTION to Arthropod diversity. Deforestation has been Forest throughout Nigeria and the rest attributed to be the aftermath of various of tropical countries are diminishing at an activities of man in his daily struggle for alarming rate of 3.5% (about 350,000-400,000 survival. Over-exploitation of the existing ha) per annum (Oyebo, 2006) in land tropical forest resources and the disappearance coverage over the past 50 years in Nigeria. of economic and other important hardwood The natural forests are increasingly being species is a threat to global biodiversity depleted in Nigeria through indiscriminate conservation and abundance of insect species extraction of economic trees and and this has become an issue of great current encroachment for other purposes such as large concern today (Sutton and Collins, 1991). scale agriculture, urbanization and industrial Watt et al. (1987) reported that the degree and development. Forest clearance, whether method of site clearance create a range of tree partial or complete, represents a major threat species diversity from monoculture to species- © 2009 International Formulae Group. All rights reserved. S. A. ADEDUNTAN / Int. J. Biol. Chem. Sci. 3(6): 1320-1335, 2009 rich mixtures. They further reported that site (Kareiva, 1983). Mortality due to natural clearance also affects the amount of ground enemies of insect herbivores is often greater in cover, in terms of plants, leaf litter and dead plant species mixtures (Kareiva, 1983). wood, and the degree of soil compaction that However, there is evidence from other studies in turn affects the soil environment for in agro ecosystems that the resource important invertebrates such as ants, termites concentration of host plants in plant species and earthworms. Hill et al. (1995) in their mixtures directly affects herbivores because study of effects of selective logging on they are more likely to find and remain in area tropical forest butterflies on Buru, Indonesia, where host plants are concentrated (Kareiva, reported that species richness, abundance and 1983). This paper presents information evenness of butterflies were all significantly concerning the impacts of different land use higher in unlogged forest than in forest logged systems on diversity and abundance of 5 years previously which they attributed to difference group of arthropods, and the greater vegetation cover at canopy and damage they caused. understory levels which made it to be more shaded below the canopy. It has been noted MATERIALS AND METHODS that species richness and diversity of insect The study areas decline with increase in human interference in This study was carried out in Akure forest ecosystem (Adeduntan et al ., 2005). Forest Reserve, Ondo State, Nigeria (Figures There are several approaches to 1 and 2). It covers an area of 69.93 km 2. The tropical forest management including three land uses selected for the study were sustainable management of natural forest, present within this reserve. Akure Forest enrichment planting and other techniques Reserve is managed by the Department of where areas of forest are partially cleared Forestry, Ondo State, Nigeria. The study site before planting, agroforestry methods and the is situated on latitude 7°18’N and longitude establishment of plantations after complete 5°02’E. A field camp was established at the clearance. Some of the silvicultural options study site to collate all insects collected and relevant to West and Central Africa are for field observations. The three land uses discussed by Lawson (1994). were adjacent to each other. The period of the The impact of plant species diversity fieldwork was eighteen months, beginning on insect diversity and damages caused by from April 2002 to September 2003. The insects has been discussed by many authors climate is humid tropical with seasonal (Altieri and Schmidt, 1986; Andrew, 1992). variation. The mean annual rainfall is about Most reports claimed that increase in plant 4000 mm with double maxima in the months diversity will subsequently lead to an increase of July and September and a short relatively in insect diversity and decrease in the risk and dry period in August. December through to extent of attack by insect pest (Altieri and February constitutes the major dry season Schmidt, 1986). The view that damage to while January and February are the driest plants is more likely to occur in monoculture months with each having less than 30 mm than in mixtures was derived mainly from rainfall (Ola-Adams and Hall, 1987). The large number of observation of agricultural relative humidity at 15 hours Greenwich and forest crops susceptible to pest attack Mean Time (GMT) is highest in the maxima (Andrew, 1992) and the smaller number of months of July and September (81%) and observations in natural ecosystems and lowest in February (44%). Temperature artificially created mixtures that show less ranges from about 20.6 °C to 33.5 °C. The herbivory (Lowman and Heatwole, 1992). monthly mean temperature is about 27 °C, a Several studies have considered the possible condition that is conducive to the ecological basis for differences in the development of tropical rainforest abundance and mixed cropping systems (Adeduntan, 2007). 1321 S. A. ADEDUNTAN / Int. J. Biol. Chem. Sci. 3(6): 1320-1335, 2009 820001 Akure F/R Oyinno Eporo Ipeli-Idoani Ala Akure-Ofosu Ifon Akure Forest Reserve Onisheri Idanre Owo Oluwa Otu LEGEND Mangrove forest and coastal vegetation. Forest reserve. Freshwater swamp forest. Lowland rainforest. 820001 10 0 10 20 Kilometers Figure 1: Forest reserves in Ondo State, Nigeria. Source – FORMECU, Abuja, Nigeria (1996). Figure 2: Map of Nigeria showing location of Ondo state. 1322 S. A. ADEDUNTAN / Int. J. Biol. Chem. Sci. 3(6): 1320-1335, 2009 Insect collection species going into extinction were identified At the centre of each of the selected and recommended for conservation. plots, five trees were tagged. The sampling protocol was targeted at free-living insect Species diversity indices herbivores foraging during the daytime on the According to Dearth and Winterborn trees nearer to the tagged sampling point. (1995), the choice of an index is complicated These include leaf-chewing (e.g. by the fact that diversity comprises two main Ledpodeptera, and Orthoptera) and sap- components namely species richness and sucking insects (Hemiptera). Sampling was species evenness. Community diversity carried out monthly for the period of 18 indices were calculated from mathematical months. During each survey, all the tagged formula that takes into account both species trees were inspected once and the insects were richness and relative abundance of each collected alive with hand and sweep nets. An species in the community. Relative frequency average of at least 30 minutes was spent at refers to the number of individuals of a given each collecting station (Basset 1999 and species divided by the total number of Adeduntan, 2007). individuals of all species found. Hand picking was used to collect crawling insects on the ground and on the RF = ni/N*100 trees. An insect Para Taxonomist was employed, as well as field assistants who were Where RF is relative frequency, trained for some time before the fieldwork ni is the number of individuals of species i , commenced. The numbers of mature and N is total number of individuals in the entire young larvae present on each tree at each population. station during each survey were recorded. All The Shannon-Weaver diversity index insect species were classified into families and was used to calculate habitat diversity orders. The frequency was obtained to following Price, (1997): Thies and Tscharntke ascertain species abundance / richness and (1999) and Steffan-Dewenter et al . (2002) species evenness. H1 = - E pi ln pi Where H1 is the Shannon diversity Tree species identification index, The botanical name of trees S is the total number of species in the encountered in the sample plots in each of habitat, land use with Dbh of not less than 10 cm was pi is the relative abundance recorded.