PART I Biological Interactions in Agroecosystems 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 9 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 10 CHAPTER 2 Biodiversity in Agroecosystems and Bioindicators of Environmental Health Maurizio G. Paoletti CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 How Many Species on the Planet and How Many Species on the Desk . . . 13 Plurality of Species Bioindicators and the Human Limited Ability to Memorize. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 What Is Biodiversity and How Can It Be Used to Assess the Landscape? . 16 What Bioindicators Are and How to Use Them . . . . . . . . . . . . . . . . . . . . . . . 17 What Is Sustainability? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Landscape vs. Landscape Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Margin Effects (Hedgerows, Shelterbelts, Weed Strips) . . . . . . . . . . . . . . . . . 21 Corridors and Connectivity in the Landscape . . . . . . . . . . . . . . . . . . . . . . . . . 23 Effect of Mosaics in the Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Colonization and Recolonization Dynamics and Pendularism. . . . . . . . . . . 25 Hedgerow Isolated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Semipermanent Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Hedgerow Network in the Landscape . . . . . . . . . . . . . . . . . . . . . . . . . 28 Grassy Semipermanent Margins, Beetle Banks . . . . . . . . . . . . . . . . . . 30 Complexity of Vegetation and Predation . . . . . . . . . . . . . . . . . . . . . . . 30 Perennials vs. Annual Crops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Impact of Pollution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Waste Disposal, Reclamation and Rehabilitation, and Bioremediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Soil Tillage and Soil Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 11 0-8493-0904-2/01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 11 Biotechnology: Genetically Engineered Plants . . . . . . . . . . . . . . . . . . . . . . . . 34 Practical Approaches for Field Assessment with Bioindicators to Monitor Decreasing Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Decreasing Environmental Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 INTRODUCTION The use of biodiversity as a tool to assess landscape structure, transfor- mation, and fate is a valid component of policies applied to rural, managed, industrial, and urbanized areas to reduce human mismanagement and alle- viate pollution (Wilson, 1997). The argument for the importance of biodiver- sity in directing environmental policy presupposes that animals, plants, and microorganisms and their complex interactions respond to human landscape management and impacts in different ways, with some organisms respond- ing more quickly and definitively than others. It has to be assumed that changes in landscape management influence the biota, and that certain tran- sient or permanent signs remain inside the system of biological communities (Richardson, 1987; Szaro and Johnston, 1996; Jeffrey and Madden, 1991; Paoletti and Pimentel, 1992). This assumption is supported by three recent books summarizing current data on insects as indicators of pollution and environmental change (Harrington and Stork, 1995; Munawar et al., 1995; and Paoletti, 1999). However, much work is needed to directly relate this assumption to the pragmatic problems encountered as attempts are made to improve the living landscape. Disappearance of species is most readily apparent in the case of birds, but- terflies, and mammals; the threatened extinction of such conspicuous organ- isms often raises public concern and garners attention from news media. For the most part, knowledge of small organisms remains conceptual, and common knowledge of the relationships between biota and their environments is approximate at best (Table 2.1); the importance of small creatures in food-chains is poorly understood or ignored (Pimm, 1991; Hammond, 1995; Paoletti, 1999). In most cases “modern” management of landscapes has supported few key plants (crops) and few animals. The agricultural revolution of the last 13,000 years has in general seen efforts concentrated on a limited number of species. This process of reducing species numbers is also the common trend in agriculture, with widespread use of systems in an early succession stage and concentration on a few short cycle plants such as cereals. Most citizens living in towns eat a limited variety of plants and animals and are aware of few invertebrates. The situation is quite the opposite in some Amazon regions dominated by the forest and/or savannas and populated by hunter- gatherers and horticulturalists (Table 2.1). Simplification in landscape management in most cases signifies main- taining the first stages of one succession and large numbers of few dominant 12 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 12 species (Odum, 1984). Most applied fields of landscape management, includ- ing agriculture, tend to deal with only a few species: monocultures are the rule both in fields and on our desks. The majority of today’s scientists, engi- neers, and university-educated professionals are trained to solve a narrow range of problems and have a limited ability to deal with complex systems (Funtowicz and Ravetz, 1993). Most successful human endeavors have involved reduction of variables (species) with positive economic results, at least in the short term. Assessing landscape quality by means of indicators based on biodiver- sity involves a substantial change in perspective not only by the experts and technicians, but also by the public and society in general. People who expect a productive, clean, and harmonious landscape that can be sustained for future generations must learn more about the diversity of life and make efforts to allow cultures that have their base in the plurality of organisms to maintain their territory and way of life. HOW MANY SPECIES ON THE PLANET AND HOW MANY SPECIES ON THE DESK At the moment, no exhaustive data base on living species exists. For this reason, estimations of existing described species oscillate between 1.3 million BIODIVERSITY IN AGROECOSYSTEMS AND BIOINDICATORS OF ENVIRONMENTAL HEALTH 13 Table 2.1 Estimated (maximum) number of species known and consumed as food by western civilized peoples and forest- and savanna-dwelling peoples in Amazonas (Venezuela). Interviews were performed by university personnel (1995–1996) using forms filled out in class; oral interviews were carried out in Amerindian villages located near Puerto Ayacucho, Amazonas (1997). Population Plants Mammals Fishes Birds Insects TOTAL Students at Padova Univ. 48 10 12 5 0 75 Guajibo Amerindians 38 22 18 18 31 127 Curripaco Amerindians 46 18 32 25 11 132 Piaroa Amerindians 68 24 18 38 28 182 Yanomamo Amerindians 125 52 56 96 89 418* The Guajibo live in the savannas near P. Ayacucho, Amazonas, Venezuela. The Curripaco are an expert river margin-dwelling group living near P. Ayacucho, Amazona, Venezuela. The Piaroa and Yanomamo are more strictly forest-living Amerindians in the Alto Orinoco, Amazonas, Venezuela. The Yanomamo maintain strong links with the forest for their survival. *Based on different sources and evaluations, the total number could be around 1400 species. 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 13 (Wilson, 1988; Wheeler, 1990) and 1.8 million (Stork, 1988) The large majority of the estimates represent small creatures, especially invertebrates. However, forecast species are some orders of magnitude even more abundant on the planet. Terry Erwin (1982) first documented the incredible projection of insects, using some South American rainforests as a model; he suggested over 30 million species (May, 1992). More recently Ehrlich and Wilson (1991) have estimated that living species could reach the 100 million mark! In fact, in the last few years, “the fondness of God for beetles and in general insects” has been extended for many other taxa such as bacteria, fungi, and many small invertebrates like mites and nematodes (Paoletti et al., 1992). There are at least two points that amaze the researcher: how many bee- tles and insect species we have on the planet and how few plant and animal species we currently consider as our possible food. In Western countries, for instance, insects as well as most small invertebrates are still considered ined- ible, in spite of the evidence supporting insects to be the large majority of liv- ing organisms. However, over 1500 species of insects are eaten worldwide, especially in tropical and Far Eastern countries (DeFolliart, 1999). In addition, many small, unconventional vertebrates such as reptilians, amphibians, and rodents, and invertebrates, such as spiders and earthworms which are referred to as minilivestock, are also used as food, especially in tropical areas (Paoletti and Bukkens, 1997). Approximately 90% of world food for people comes from just 15 plant and 8 animal species (Wilson, 1988). However, the use of biodiversity is incredibly different among different human groups. In Java, small farmers cultivate 607 crop species in their gardens, with an over- all species diversity comparable to deciduous subtropical forests (Dover and Talbot, 1987; Michon, 1983). In Swaziland, 220 wild plant species are com- monly consumed (Ogle and Grivetti, 1985). Among the Caiçara coastal com- munities of the Atlantic forest, up to 276 plants are used, of which 88 are for medicine (Rossato et al., 1999). Andean farmers cultivate many clones of potatoes, more than 1000 of which have names (Clawson, 1985). In northeast Italy (Friuli), an old tradition of wild plant gatherings in spring culminates in 54 different species (Paoletti et al., 1995). Amerindians collect hundreds of plants and edible animals. In most cases, people living in tropical areas have a better developed attitude toward using a variety of creatures. For instance, Martin et al. (1987) have cited about 2000 edible perennial fruits in the trop- ics. In the tropics as elsewhere, modernization and market economies have in many cases reduced in practice the number of species and varieties used as food and medicine, and a strong effort has to be made to reinforce local native knowledge about biodiversity and to maintain it into schools and societies. For example, more recent colonizers, such as the Caboclos in the Brazilian Amazon and the Caiçaras in the Atlantic forest have a limited use of insects as food (respectively three and one species, compared with the Amerindians living in the Amazon, such as the Yanomamo Ye’kuana, and Piaroa, who con- sume many different species (Paoletti and Dufour, 2000). Likewise, villagers near larger cities in the Amazonas, Venezuela, have a limited knowledge of 14 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 14 animals, plants and insects as food compared with villagers farther from the town. Maintaining high interest for the diversity of plants, animals, and local uses is the way to maintaining the diversity of natural resources. Maintaining and promoting biodiversity means keeping knowledge and local cultures alive. However, to manage and consider diversity as a chance for human life, one must consider limits in the human capability to memorize the living crea- tures, and then account for plurality of species. PLURALITY OF SPECIES BIOINDICATORS AND THE HUMAN LIMITED ABILITY TO MEMORIZE How can people be made aware of the 600 to 3000 species of inverte- brates living in most mixed landscapes in temperate countries or the perhaps 5000 to 18,000 species in tropical forested landscapes (Paoletti et al., 1992; Hammond, 1992)? As each species has at least several different larval stages and sometimes exhibits sexual dimorphism and variability in color pattern, the information for each species must be multiplied at least five- to sixfold and multiplied again if varieties of each species are included. Books, book figures, and taxonomic identification keys are useful but, with some exceptions, are suited only for experienced researchers. Open identification systems afforded by computer programs greatly facilitate the task of classifying organisms that at first glance are very similar in appear- ance (see the Lombri CD-ROM developed for earthworm identification by Paoletti and Gradenigo, 1996). The new approach to accomplishing the first step of any biodiversity study is the correct identification of the organisms present in a system. The aim of bioindicator-based studies is to use the living components of the environment under study (especially those with the highest diversity, the invertebrates) as the key to assess the transformations and effects, and, in the case of landscape reclamation, to monitor the remediation process in differ- ent parts of the landscape over time. This approach could improve policies aimed at reducing the stress placed on landscapes. For example, bioindicator- based studies could help the process of ameliorating and remediating the rural landscape as a result of policy implementation, such as the set-aside in Europe (Jordan, 1993; Jorg, 1994). Reductions in agricultural pesticide use could be adequately monitored by bioindicators to assess the benefit of a new policy (Pimentel, 1997; Paoletti, 1999). Bioindicators could also be used to assess and remediate contaminated areas or polluted areas to be reclaimed (Van Straalen and Krivolutsky, 1996). Such applications of bioindicators can be expected to help not only to improve the environment but also to augment awareness of the living crea- tures around, so that a better appreciation of the crucial role in sustaining life on the planet is obtained. BIODIVERSITY IN AGROECOSYSTEMS AND BIOINDICATORS OF ENVIRONMENTAL HEALTH 15 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 15 WHAT IS BIODIVERSITY AND HOW CAN IT BE USED TO ASSESS THE LANDSCAPE? Without biodiversity life on earth would be impossible. Based on recent estimates, biodiversity accounts for between 319 billion and 33,000 billion dollars per year in value (Pimentel et al. 1997; Costanza et al., 1997) (Table 2.2). Biodiversity encompasses all of the species, food-chains, and biological patterns in an environmental system, as small as a microcosm or as large as a landscape or geographic region (Heywood and Watson, 1995; Wilson, 1988; 1997). The concept of biodiversity has grown with the perception of its loss increasing human impact and mismanagement of the environment (Wilson, 1988). Whether on a local, regional, or global scale, reduced biotic diversity is associated with increased environmental stress and reduced environmental heterogeneity (Erwin, 1996). Biodiversity implies an environment rich in dif- ferent organisms and can be read as a system in which species circulate and 16 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Table 2.2 Total estimated economic benefits of biodiversity in the United States and worldwide (Modified from Pimentel et al., 1997). Data in billions of U.S. dollars. ACTIVITY United States World Waste disposal 62 760 Soil formation 5 25 Nitrogen fixation 8 90 Bioremediation of chemicals 22.5 121 Crop breeding (genetics) 20 115 Livestock breeding (genetics) 20 40 Biotechnology 2.5 6 Biocontrol of pests (crops) 12 100 Biocontrol of pests (forests) 5 60 Host plant resistance (crops) 8 80 Host plant resistance (forests) 0.8 11 Perennial grains (potential) 17 170 Pollination 40 200 Fishing 29 60 Hunting 12 25 Seafood 2.5 82 Other wild foods 0.5 180 Wood products 8 84 Ecotourism 18 500 Pharmaceuticals from plants 20 84 Forests’ sequestering of carbon dioxide 6 135 TOTAL 319 2928 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 16 interact. Structure, scale, and features of the landscape also enter into the def- inition of biodiversity. Although human activities do not invariably work against biodiversity, they can strongly reduce it; for example, in agriculture, productivity of a crop per unit of time and market opportunity almost always make monoculture cropping more profitable and convenient (Odum, 1984; Paoletti et al., 1989; Paoletti and Pimentel, 1992). However, this is not always the case, as demon- strated by the fact that, both in temperate and tropical areas, certain practices of polyculture and agroforestry or specialized types of agriculture (organic or integrated farming) can maintain high biodiversity while at the same time producing adequate returns for farmers (Altieri, 1999; DeJong, 1997; Paoletti et al., 1993). It has also been observed that some urban areas support greater numbers of species (such as of birds) than the surrounding rural landscape dominated by monocultures and landscape simplification under high input (Paoletti and Pimentel, 1992). Careful analysis of apparently “unmanaged” primary rain forests demon- strates that, in addition to being manipulated by their “original” components, they are sometimes strongly influenced by human activities as well. The well- studied case of the relationship between the Kayapo Indians and their envi- ronment in the Brazilian Amazon (Posey, 1992) may have many similar, unstudied equivalents, e.g., the Yanomamo, Piaroa, Curripaco, and Makiritare Indians (living in the Alto Orinoco, Amazonas,Venezuela). The Makiritare have been observed actively disseminating their favored edible white benthic earthworms (motto) on the beaches of affluents of the Padamo river. Likewise, the hedgerows found in many European landscapes (in some cases originat- ing with the Ancient Roman centuriations; Paoletti, 1985) and the terracing used in Mediterranean agriculture are associated with increased numbers of species and landscape diversity (Paoletti and Pimentel, 1992). In Liguria, Italy, the pre-bugium, for instance, is a mixture of several edible wild herbs collected especially on walls adopted to terrace the steep rural landscape. WHAT BIOINDICATORS ARE AND HOW TO USE THEM The concept of bioindicators is a trivial simplification of what probably happens in nature. It can be defined as a species or assemblage of species that is particulary well matched to specific features of the landscape and/or that reacts to impacts and changes (Paoletti and Bressan, 1996; VanStraalen, 1997). Examples of bioindicators are species that cannot normally live outside the forest, that live only in grasslands or in cultivated land, that support high lev- els of pollutants in their body tissues, that react to a particular soil manage- ment practice, and that support waterlogging. Bioindication is not a new term; it has evolved from geobotany and environmental studies from the last century (Paoletti et al., 1991). It has become an important paradigm in the process of assessing damaged and contaminated areas, monocultures, BIODIVERSITY IN AGROECOSYSTEMS AND BIOINDICATORS OF ENVIRONMENTAL HEALTH 17 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 17 different input farming, different tillage systems, contaminated orchards, disposal areas, industrial and urban settlements, and areas neighboring power plants. In empirical terms a bioindicator can be thought of as a label for a partic- ular situation and environmental condition. However, this is a very simplis- tic view. Although the identification of a species as a label for a particular environment can be convincing, rapid changes in landscape use, especially in the mosaic situation, can reduce the bioindicative value of a particular species. All species react to environmental changes and can adopt new pat- terns and behavior to cope with the change; the many pest species that have evolved from wild, nonpest species is an obvious example of this phenome- non. Evolutionary mechanisms involving species are not absent in the man- aged area. The disappearance of a single species from a landscape can be traced from either a complex combination of events, including the collapse of metapopulations as affected by reduction of connectivity (e.g., margins, lanes, hedgerows, riverbanks), or to a single major event, such as field dimen- sion, tillage, or field contamination (Burel, 1992). Instead of focusing on a few indicator species, more reliable information can be gained from studies of a set of species or a higher taxon, with meas- urements made not at the level of presence/absence but as numbers, bio- mass, and dominance. The use of guilds such as detritivores, predators, pollinators, parasitoids, dung decomposers, and carrion scavengers as bioindicators can reveal interesting differences in the landscape. Patterns of herbivory in polluted areas, e.g., the abundance of aphids on trees or mining lepidoptera, have been correlated with industrial pollution and in particular with increased levels of available nutrients (free amino acids) in the stressed trees (Holopainen and Oksanen, 1995). A study in Denmark showed that the complex of parasitoid Hymenoptera (up to 164 species) living in cereal field soils can accurately discriminate between fields that have been spread with the currently used pesticides and untreated fields (Jensen, 1997). The importance of fungivores in detecting cereal fields with and without pesticide (fungicide) inputs has also been shown (Redderson, 1995). For example, the detritivores were demonstrated to be a fine way to discriminate organic apple orchards from conventional apple orchards (Paoletti et al., 1995). WHAT IS SUSTAINABILITY? Table 2.3 shows the potential meaning and the current use of the term sustainability, focusing on the aspect of stability over time. In terms of the environment, sustainability signifies maintaining the productivity and potential of an ecosystem used by humans with time. This theoretical situa- tion normally never happens in practice (Conway and Barbier, 1990; Altieri, 1995). As discussed by Carter and Dale (1974) and Ponting (1991), most 18 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920103_CRC20_0904_CH02 1/13/01 10:39 AM Page 18 [...]... 920 103_CRC20_0904_CH 02 36 1/13/01 10:39 AM Page 36 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 50 49 44 40 60 29 28 30 33 30 50 28 40 20 12 30 20 10 Total number of species 0 31 30 13 11 9 12 ARANEAE CARABIDAE FORMICIDAE 2 1 6 6 6 6 5 BRACONIDAE 4 5 5 5 CHILOPODA 3 4 3 4 ISOPODA 3 3 3 1 2 OPILIONES 3 3 3 0 2 2 DIPLOPODA 9 B1 B2 10 8 11 12 C1 C2 20 40 60 78 80 86 93 100 109 120 128 123 Figure... connectivity in the landscape (Joenie et al., 1997) In many cases, these 920 103_CRC20_0904_CH 02 22 1/13/01 10:39 AM Page 22 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Table 2. 4 Farming systems that can augment biodiversity in agroecosystems (Modified from Paoletti et Sommaggio, 1996; Paoletti, 1999 modified) Sustained Invertebrate Biodiversity 11, 12, 17 hedgerows dikes with wild herbage11, 12. .. STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT knowledge of the smallest living creatures that populate all corners of landscapes When designing and carrying out bioindicator-based studies, it must be kept in mind that incertitude linked to limited knowledge and variability in the field can lead to disappointment and/ or excessive expectations Prudence is always required in interpreting field... traditional farming landscapes in many tropical and temperate countries Weedy margins (sometimes used as paths for machinery), ditches, fences, walls, and enclosures all create margins These structures, in particular hedgerows and shelterbelts, serve many purposes, including providing a source of wood for burning and building, securing emergence fodder, providing a microclimate, and improving diversity and connectivity... the landscape The layout of the fields (dimension and shape) can also affect movements and colonization patterns of herbivores and predators (Paoletti and Lorenzoni, 1989; Sommaggio et al., 1995)  920 103_CRC20_0904_CH 02 24 1/13/01 10:39 AM Page 24 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 2. 1a/b/c A Nitrogen microbial biomass is in general more abundant in an alfalfa margin... reasons, including the following: • • • • better short-term productivity; rapid crop maturation; limited susceptibility to predators, pathogens, and pests; less risk in case of war, invasions, fire, etc  920 103_CRC20_0904_CH 02 32 1/13/01 10:39 AM Page 32 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT For example, an apple orchard needs at least three years to become productive; in tropical... harm soil invertebrate macrofauna (Paoletti, 1985) Soil compaction in fields can be increased by passing heavy machinery, trucks, and other heavy equipment As with deep tillage, compaction can reduce the biomass and diversity of most soil organisms (Stinner and House, 920 103_CRC20_0904_CH 02 34 1/13/01 10:39 AM Page 34 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 1990; Paoletti and Bressan,... abundant carabid beetles in a cereal field Oecologia, 92: 373–3 82 Lys, J.A and A Nentwig, 1994 Improvement of the overwintering sites for Carabidae, Staphylinidae and Araneidae by strip -management in cereal field Pedobiologia, 38 :23 8 24 2 Lys, J.A., M Zimmermann, and W Nentwig, 1994 Increase in activity density and species number of carabid beetles in cereals as result of strip -management Entomologia... surrounding fields the same role of islands that are recolonized by the continent However, at the end of the season fields can be highly dense in invertebrate populations that in a pendular mechanism recolonize their “continent.” Then predators and parasitoids that can find shelter and overwinter in such “continents” will be better fitted to stay in the landscape (Figure 2. 4)  920 103_CRC20_0904_CH 02 26... colonize fields nearby hosting short cycle crops (such as 920 103_CRC20_0904_CH 02 28 1/13/01 10:39 AM Page 28 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT n eggs and larvae / plant Northeastern of Italy 5 2 Hedgerow Field 1 0 0, 0 Jun Figure 2. 3 Jul Ago Hedgerow effect on Syrphidae distribution in corn field Close to the hedgerows, eggs and syrphid larvae appear earlier in the season Syrphids . 1995). BIODIVERSITY IN AGROECOSYSTEMS AND BIOINDICATORS OF ENVIRONMENTAL HEALTH 23 920 103_CRC20_0904_CH 02 1/13/01 10:39 AM Page 23 24 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 2. 1a/b/c. Carter and Dale (1974) and Ponting (1991), most 18 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT 920 103_CRC20_0904_CH 02 1/13/01 10:39 AM Page 18 BIODIVERSITY IN AGROECOSYSTEMS AND. (Table 2. 1). Simplification in landscape management in most cases signifies main- taining the first stages of one succession and large numbers of few dominant 12 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS