Biotic Diversity in Agroecosystems

353 Pages·1992·50.12 MB·English

by  D. Pimentel and Maurizio G. Paoletti (Eds.)

BI0TIC DIVERSITY
IN AGROECOSYSTEMS
Papers from a symposium on Agroecology and Conservation Issues in Tropical
and Temperate Regions, University of Padova, Padova, Italy, 26-29
September 1990
Edited by
M.G. Paoletti
Department of Biology, Padova University, Via Trieste 75, 35121 Padova, Italy
and
D. Pimentel
Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY
14853-0999, USA
Reprinted from Agriculture, Ecosystems and Environment, Vol. 40 Nos. 1-4 (1992)
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1
Introduction
The preservation of biodiversity (see the paper on number of living spe­
cies ) appears to be a high priority among biologists, ecologists, and environ­
mentalists. Although this group understands the impact that human activities
have on biodiversity, few studies have focused on the importance of biodiv­
ersity in natural and agricultural ecosystems. Others, less familiar with the
diverse interactions that occur among plants and animals, seem to have little
appreciation or understanding of ecological principles and the benefits that
diversity of natural biota have for humans and the environment.
The reasons for the existing historical and philosophical perspective are
many. For instance, when some agriculturalists assess pests, they generally
focus their attention on the animal-plant food-web operating within the spe­
cific crop. Rarely do they examine the relationship of crop pest problems to
the environments surrounding corn or soybean fields. Generally, crop breed­
ing, irrigation, fertilizers, pesticides, and machinery are considered as one
problem with one solution centered on the crop. Although this approach has
been successful in increasing many crop yields, it also has contributed to the
development of several serious environmental and biodiversity problems in
agriculture. These include: soil erosion; rapid water runoff; fertilizer and pest­
icide pollution of soil and water; salinization; loss of biodiversity; water-log­
ging, to mention but a few. Some agriculturalists, engineers and others appear
to underestimate the degree of species richness in agroecosystems and the
benefits these natural biota contribute to agriculture and a healthy nature.
Clearly, agroecology and landscape ecology can play a major role in protect­
ing the environment and conserving biological diversity.
Many of the practical opportunities for improving the sustainability of ag­
riculture and making it more environmentally sound were discussed at the
International Symposium on Agroecology and Conservation Issues in Tem­
perate and Tropical Regions, held in September 1990 at the University of
Padova. Of the large number of papers that were presented at the Sympo­
sium, a total of 22 papers have been assembled here.
Several papers deal with strategies for increasing biodiversity in agricul­
tural landscapes. Other papers point out that agriculture must meet the grow­
ing need for food and will continue to spread into forests and other natural
areas. Although some positive interactions may result from this, negative in­
teractions, with the 30-80 million species estimated to be on this planet, will
increase. Although humans appear to recognize the value of crop and live­
stock species, few really appreciate the fact that agriculture and forestry can-
2 M.G. PAOLETTI AND D. PIMENTEL
not function in a productive, sustainable way when significant numbers of
species in natural biota are lost.
Sustainable agricultural technologies, that improve the environment within
and outside farms, offer many opportunities to increase biodiversity in the
landscape (Paoletti et al.). Related to this, microbial biomass and diversity
appear to depend on the amount of organic matter in soils (Dick). Also soil
invertebrates (Crossleyetal.),microrizhes (RosemeyerandGleissman) and
legume plants can be linked to improve agricultural and productive environ­
ments. Hedgerows on field margins are another important part of some agri­
cultural landscapes (Kromp; Dennis and Fry; Lagerlof et al.). Often improv­
ing the mosiac structure of landscape habitats improves the dynamics of
predator/parasitoid-herbivore food chains while at the same time promoting
species conservation in agroecosystems (Banaszak; Booij; Hassall et al.;
Samways).
Biodiversity should be monitored both in the crops and in soils because
many natural species are essential to sustainable agricultural programs
(Foissner; Koehler). Of course, the management of plant types in the agro-
ecosystem are basic to effective biological resources management. Sound crop
management systems will reduce the dependence of agriculture on fertilizers
and pesticides (Garcia, Enache and Ilnicki).
The inclusion of new crops into agricultural systems increases the diversity
of agriculture, reduces soil erosion, and reduces fertilizer needs (Becker et
al.). The prime source of new crop types still remains the tropics (Bjornda-
len; Carpaneto and Germi; De Miranda and Mattos; Greenslade). Therefore,
more investigations must be focused on the diversity of plants and animals in
tropical as well as temperate regions. Humans need to protect and conserve
all species, large and small. All play an important part in maintaining agricul­
ture and the environment, and enhancing the lives of human society.
This publication has been made possible through the efforts of the follow­
ing institutions and persons: the European Economic Community; the Ve-
neto Regional Board; Ente Svilnppo Agricolo del Veneto; Comitato Nazion-
ale delle Ricerche; the Padova Chamber of Commerce. In particular we would
like to thank the president of Padova University, M. Bonsembiante; A. Za-
morani, D. Agostini and O. Ferro from the Faculty of Agriculture, Padova
University; G.G. Lorenzoni, A.G. Levis and V. Albergoni from the Depart­
ment of Biology, Padova University. Mirella Soratroi and Brony Falinska
helped with the editorial work. Hetty Verhagen helped to transform the man­
uscripts into a complete volume.
M.G. PAOLETTI
(Padova, Italy)
D. PIMENTEL
(Ithaca, NY, USA)
3
Agroecosystem biodiversity: matching production
and conservation biology
M.G. Paolettia, D. Pimentelb, B.R. Stinnerc and D. Stinnerc
aDepartment of Biology, Padova University, Via Trieste 75, 35100 Padova, Italy
bDepartment of Entomology, Cornell University, Ithaca, NY, USA
""Department of Entomology, Ohio State University, Wooster, OH, USA
ABSTRACT
Paoletti, M.G., Pimentel, D., Stinner, B.R. and Stinner, D., 1992. Agroecosystem biodiversity: match­
ing production and conservation biology. Agric. Ecosystems Environ., 40: 3-23.
A review of the existing literature on biodiversity connected with agricultural activities has been
developed, and the possible sustainable alternatives have been looked into.
Following recent evaluations, only one-twentieth to one-sixtieth of the planet's species have yet
been described and most of these will be lost if the destruction of the environment continues at its
present rate. Most of the terrestrial environment (up to 95%) is affected by human activities includ­
ing agriculture and the terrestrial habitats provide up to 98% of human food on the planet. Sustainable
strategies in food production in agriculture improve the existing biodiversity and include the follow­
ing items: increased porosity of the landscape through proper management of natural vegetation, bet­
ter use and recycling of organic residues, introduction of integrated farming systems, reduced tillage,
rotation, biological control, increased number of biota involved in human food-webs.
INTRODUCTION
Why are we concerned about the biotic diversity in space, in time in the
anthropized cultivated areas? Is the sufficient production of foods, fiber and
meat reasonably consistent with the conservation of biodiversity? Biodivers­
ity is associated with terrestrial areas in which diversity of natural biota play
the same social and economic roles as do "libraries, universities, museums,
symphony halls, and newspapers. They must be integrated with the educa­
tional system in the same way as these other complex information storage and
transfer systems" (Janzen, 1988). Most demographic, social, economic and
environmental problems occur in tropical areas and it is difficult to convince
the public about the 'library excellence' of natural biota when they are with-
Correspondence to: M.G. Paoletti, Department of Biology, Padova University, Via Trieste 75,
35100 Padova, Italy
4 M.G. PAOLETTI ET AL.
TABLE 1
Numbersof described species of living organisms (from Wilson, 1988)
Kingdom and major Common name No. of described Totals
subdivision species
Virus Viruses 1000 1000
(order of magnitude
only)
Monera
Bacteria Bacteria 3000
Myxoplasma Bacteria 60
Cyanophycota Blue-green algae 1700 4760
Fungi
Zygomycota Zygomycete fungi 665
Ascomycota Cup fungi 28650
(including 18000 lichen
fungi)
Basidiomycota Basidiomycete fungi 16000
Oomycota Water molds 580
Chytridiomycota Chytrids 575
Acrasiomycota Cellular slime molds 13
Myxomycota Plasmodial slime molds 500 46983
Algae
Chlorophyta Green algae 7000
Phaeophyta Brown algae 1500
Rhodophyta Red algae 4000
Chrysophyta Chrysophyte algae 12500
Pyrrophyta Dinoflagellates 1100
Euglenophyta Euglenoids 800 26900
Plantae
Bryophyta Mosses, liverworts, 16600
hornworts
Psilophyta Psilopsids 9
Lycopodiophyta Lycophytes 1275
Equisetophyta Horsetails 15
Filicophyta Ferns 10000
Gymnosperma Gymnosperms 529
Dicotyledoneae Dicots 170000
Monocotyledoneae Monocots 50000 248428
Protozoa Protozoans: 30800
Sarcomastigophorans,
ciliates, and smaller groups 30800
Animalia
Porifera Sponges 5000
Cnidaria, Ctenophora Jellyfish, corals, comb 9000
jellies
AGROECOSYSTEM BIODIVERSITY 5
Kingdom and major Common name No. of described Totals
subdivision species
Platyhelminthes Flatworms 12200
Nematoda Nematodes (roundworms) 12000
Annelida Annelids (earthworms and 12000
relatives)
Mollusca Mollusks 50000
Echinodermata Echinoderms (starfish and 6100
relatives)
Arthropoda Arthropods
Insecta Insects 751000
Other arthropods 123161
Minor invertebrate
phyla 9300 989761
Chordata
Tunicata Tunicates 1250
Cephalochordata Acorn worms 23
Vertebrata Vertebrates
Agnatha Lampreys and other jawless
fishes 63
Chrondrichthyes Sharks and other
cartilaginous fishes 843
Osteichthyes Bony fishes 18150
Amphibia Amphibians 4184
Reptilia Reptiles 6300
Aves Birds 9040
Mammalia Mammals 4000 43853
Total — all organisms 1392485
out enough food for their families and they live in absolute poverty (De Mi­
randa and Mattos, 1992).
Organic material equivalent to 38.8% of the present net primary produc­
tion of the planet is today appropriated entirely by humans (Vitousek et al.,
1986). One-third of the global land surface of the planet still is wilderness
(48.069X 106 km2) (McCroskey and Spalding, 1989) but most of this area
has humans living in the wilderness regions (Western, 1989).
The amount of species on the planet (that means biological units, which
are diverse genetically and ecologically) is estimated between 30 and 50 mil­
lion according to Erwin (1982, 1988). Only 1 392 485 (Table 1) species are
scientifically described according to some inventories (Parker, 1982; Arnett,
1985; Kevan, 1985; Wilson, 1988; Minelli, 1989; Pimentel et al., 1992a) or
something more, 1.7-1.8 million (Stork, 1988; May, 1990). Discrepancies
between the amount forecasted and the described number of species implies
defects in understanding our planet's structure, composition, diversity and
6 M.G. PAOLETTI ET AL.
complexity. No matter that the number of biota in the planet is far larger
than, for instance, the artefacts. The number of chemical compounds artifi­
cially created by our technology is difficult to quote but 60 000 chemicals are
presently in use in the US (National Toxicology Program, 1981). However
the US is home for an estimated 500 000 living species of which 95% are
small organisms (Knutson, 1989).
An inventory of the warehouse is needed before we can elaborate the strat­
egy for the use or manufacture of goods. On our planet, knowledge of biota is
limited and scanty. For instance, there are only 3000 scientists who specialize
in tropical biology and 1500 taxonomists who are devoted to the tropical areas
(Raven, 1980; Myers, 1985). Can we use the existing biodiversity better and
can we conserve it? Can we assign a real value to biotic diversity? It has been
argued: "I cannot help thinking that when we finish assigning values to bio­
logical diversity we will find that we do not have very much biological diver­
sity left" (Erenfeld, 1988).
On a global scale of ecology and brain-storming the Gaia Hypothesis re­
lated to the interactions of biotic activity and most climatic and abiotic fac­
tors (Lovelock, 1989; Hinkle and Margulis, 1990), we need efforts to inves­
tigate the composition and differentiation of the living biota. In particular,
interactions between agriculture and biodiversity are important (Pimentel et
al., 1992a). About 70% of the earth's ecosystems (50%, agriculture including
pastures; 20%, forests) are manipulated to obtain 98% of the food fiber and
wood used by humans (Food and Agriculture Organization, 1981; Vitousek
et al., 1986; Western, 1989; Pimentel et al., 1992a). In addition, about 25%
of the land is devoted to urbanization and human settlements. Thus, humans
occupy and manage approximately 95% of the earth's terrestrial ecosystems
(Western, 1989).
We maintain that each species has intrinsic value. Earthworms, insects,
herbs, fungi or bacteria are no less fascinating or less worthy of our interest
and conservation than the larger 'Noah's Ark' organisms such as elephants,
birds and sequoias (Pimentel et al., 1992a).
Some questions that should be addressed are: which part of the existing
biota is living in cultivated or human occupied areas which cover the majority
of the terrestrial areas; how many are living in wild protected areas; are the
two components interchangeable; are the biota living in the wilderness pos­
sible pests for crops; can the diversity of biota be used as a tool for develop­
ment and improve the well-being of humans?
We are not capable of giving exhaustive responses to these questions but
we hope to demonstrate that opportunities exist to conserve biodiversity in
agriculture and forestry.
THEORETICAL BASES OF BIODIVERSITY ESTIMATIONS
At least three guidelines provide estimates of the biotic diversity on the
planet. These include the following.
AGROECOSYSTEM BIODIVERSITY 7
Food-web structures and dimensions
The richness of a food-web and the length of food-chains are predicted to
be higher in tropical areas than in temperate habitats (Pimm and Lawton,
1977; Kitching and Pimm, 1985; Kitching, 1990). Because of food-web com­
plexity and number, food-web abundance implies a large number of species.
In tropical areas, food-webs are more numerous than in temperate areas
(Pimm and Lawton, 1977; Cohen et al., 1990). In cultivated areas many food-
webs are missing or unstable (Odum, 1984). For instance, pesticide residues
affect soil detritivores and predators (Pimentel and Edwards, 1982; Paoletti
etal., 1988, 1992; Pimenteletal., 1991).
Body dimensions
Data are projected from some regression figures obtained by plotting the
mean body length and the number of species (May, 1986). Using the body
length assumption for small organisms (0.5 mm) to be similar for all orga­
nisms the rate of known and unknown species is one to 10, that means 10
million species on the planet (May, 1986, 1988, 1990).
Extrapolations following geographical endemism and host specificity
Based on an examination of the geographic and host specificity, May (1988,
1990) stated that an estimate of animal species is possible. Based on the es­
timated 300 000 living plant species in the tropics and 10 insect species per
tree, it is calculated that there are 3 000 000 species of associated insects.
Erwin (1982) calculated that with 600 non-shared beetle species per tree
and 50 000 tree species, the total beetle species is 30 million. More recently
Erwin (1988) sorting the materials collected in the canopy of the Tambapora
rain forest in Peru has estimated the value to be more than 50 million insect
species. Based on this estimation and current deforestation, Erwin reported
that several million species will be lost if forest destruction is not stopped.
These estimates were discussed by Stork (1988), Adis (1990), May (1990),
Hodkinson and Casson (1991) and Paoletti et al. (1990, 1991a). In partic­
ular Stork (1988) estimates between 7.3 and 81.4 million arthropod species
in the tropical rain forests. Other estimations based on species-area curves
have been given (Simberloff, 1986; Reid and Miller, 1989).
DESTRUCTION RATE AND LOSS OF INFORMATION
From 250 000 to 750 000 plant species are estimated to exist in the world,
with 65% found in the tropics (Farnsworth, 1988; Wilson, 1988). Chemical,
folklore and pharmaceutical data are found for as many as 25 000 plant spe-
M.G. PAOLETTI ET AL.
TABLE 2
Estimates of potential species extinction in the tropics
Estimate Basis of estimate Source
From 1950 to 1980 one half of Whittaker and Likens, 1975
previously living species
One species day-' to one species Unknown Myers, 1979
hr"l between 1970s and 2000
33-50% of all species between A concave relationship Lovejoy, 1980
1970s and 2000 between percentage of forest
area loss and % of species
loss
A million species or more by end If present land-use trends National Research Council, 1980
of this century continue
As high as 20% of all species Unknown Lovejoy, 1981
50% of species by the year 2000 Different assumptions and Ehrlich and Ehrlich, 1981
or by the beginning of next an exponential function
century
Several hundred thousand species Unknown Myers, 1982
in just a few decades
25-30% of all species, or from Unknown Myers, 1983
500000 to several million by
the end of this century
500000-600000 species by the Unknown Oldfield, 1984
end of this century
33% or more of all species in the Present rates of forest loss Simberloff, 1983
21 st century will continue
20-25% of existing species by the Present trends will continue Norton, 1986
next quarter of century
15% of all plant species and 2% of Forest regression will Simberloff, 1986
all plant families by the end of proceed as predicted until
this century 2000 and then stop
completely
0.75 million species by the end of All tropical forests will Raven Missouri Botanical
this century disappear and half their Gardens, (Lugo, 1988)
species will become extinct
20-30 million species If 50% of rainforests are Erwin, 1988
destroyed by the year 2000