insect ecology and population dynamics - pstu.ac.bd web viewthe word population (l. ... protozoa,...

Insect Ecology and Population Dynamics

Introduction

Life does not exist in a vacuum Every living organism is surrounded by materials and

forces which constitutes its environment and from which it must derive its need Thus for its

survival a plant an animal or a microbe cannot live completely sealed in an impervious skin or

shell but requires from its environment-a supply of energy a supply of materials and a removal

of waste products For these basic requirements each living organism has to depend and also to

interact with different non-living or abiotic and living or biotic components of the environment

The biotic environmental components include basic inorganic elements and compounds such as

water and carbon dioxide calcium and oxygen carbonates and phosphates and an array of

organic compounds the by-products of organisms activity or death They also include such

physical factors as soil rainfall temperature moisture winds currents and solar radiation with

its concomitants of light and heat The biotic environmental factors comprise plants animals and

microbes all of which interact in a fundamentally energy-dependent fashion The scientific study

of the interactions of organisms with their physical environment and with each other is called

ecology (Helena Curtis 1975) It mainly occurs with the directive influences of abiotic and

biotic environmental factors over the growth distribution behavior and survival of organisms

(Herreid II 1977)

Definition

The author who was the first coin of the term ecology is uncertain however many

biologists grant credit to the German zoologist Ernst Haeckel who used the term as oekologie

in 1869 to refer to the inter-relationship of living organisms and their environment

The word ecology comes from two Greek words oikos meaning household or home

or place to live or habitation and logos meaning discourse or study Thus literally

ecology deals with the organism and its place to live Basically organisms place to live its

environment so ecology is also called environmental biology (Smith 1977)

Ecology is the scientific study of the relationships of living organisms with each other

and with their environments It is the science of biological interactions among individuals

populations and communities and also of ecosystems-the inter-relations of biotic communities

with their non-living environments


Conventionally ecology has been defined variously by different classical and modern

ecologists with different view of points Quite oddly no universally accepted definition of

ecology has been formulated by any ecologists so far and for the better understanding of scope

limitations purpose and mode of study of different ecological phenomena one has to go through

following chronologically arranged definitions of ecology

Ernst Haeckel (1869) defined ecology as the body of knowledge concerning the economy of

nature- the investigation of the total relations of animal to its inorganic and organic

environment

British ecologist Charles Elton (1927) defined ecology as the scientific natural history

concerned with the sociology and economics of animals

Taylor (1936) preferred to define ecology as the science of the relations of all organisms to all

their environments

A much broader definition of ecology of Allee et al (1949) considered ecology as the science

of inter-relation between living organisms and their environment including both the physical

and biotic environments and emphasizing inter-species as well as intra-species relations

SC Kendeigh (1961) defined ecology as the study of animals and plants in their relation to

each other and to their environment

Andrewartha (1961) defined ecology as the scientific study of the distribution and abundance

of animals

Odum (1963) defined ecology as the study of the structure and function of nature ecosystem

approach

GAPetrides (1968) defined ecology as the study of environmental interactions which control

the welfare of living things regulating their distribution abundance production and evolution

Krebs (1972) defined ecology as the scientific study of the interactions that determine the

distribution and abundance of organisms

Southwick (1976) defined ecology as the scientific study of the relationships of living

organisms with each other and with their environments He further elaborates his definition of

ecology by saying that it is the science of biological interactions among individuals

populations and communities and it is also the science of ecosystems-the inter-relations of

biotic communities with their non-living environments


Price (1984) defined ecology as the science of relationships of organisms to their environment

Insect ecology Insect ecology defined as the scientific study of the interactions (functional

process) that determine the distribution and abundance of true insects population in a specific

habitat

Objectives PurposesEcology is a distinct science because it is a body of knowledge not similarly organized in

any other division of biology because it uses s special set of techniques and procedures and

because it has a unique point of view The essence of ecology lies in the comprehensive

understanding of the meaning of following phenomena

1 The local and geographical distribution and abundance of organisms (habitat niche

community biogeography)

2 Temporal changes in the occurrence abundance and activities of organisms (seasonal

annual successional and geological)

3 The inter-relations between organisms in populations and their communities

(population ecology)

4 The structural adaptations and functional adjustments of organisms to their physical

environment (physiological ecology)

5 The behaviour of organisms under natural conditions (ethology)

6 The evolutionary development of all these inter-relations (evolutionary ecology)

7 The biological productivity of nature and its best use to mankind (ecosystem

ecology)

8 The conservation and management of natural resources (applied ecology)

Branches of ecologyEarly ecologists have recognized two major subdivisions of ecology in particular

reference to animal or to plants hence animal ecology and plant ecology But when it was

found that in the ecosystems plants and animals are very closely associated and inter-related

then both of these major ecological subdivisions became vague However when animals and

plants are given equal emphasis the term bioecology is used


Further ecology is often broadly divided into autecology and synecology Autecology

deals with the ecological study of one species of organism Thus an autecologist may study the

life history population dynamics behaviour home range and so on of a single species such as

the Maize-borer Chilo partellus Synecology deals with the ecological studies of communities or

entire ecosystems Thus a synecologist might study deserts or caves or tropical forests

Besides these major ecological subdivisions there are following specialized branches of ecology

1 Habitat ecology It deals with ecological study of different habitats on planet earth and

their effects on the organisms living

2 Organismal Ecology Evolutionary adaptations that enable individual organisms to

survive in their environment

3 Population Ecology Studies of the manner of growth density structure and regulation of

population of organisms and how members of a population coexists

4 Community Ecology Studies of the local distribution of animals in various habitats the

recognition and composition of community units and succession which indicate how

interactions between species (competition predation and symbiosis) affect community

structure and organization

5 Ecosystem Ecology Broadens to include the interactions of communities with all the

abiotic factors taken into consideration This branch of ecology often places research

emphasis upon energy flow and chemical cycling between living and non-living

components among and between communities

6 Biosphere Ecology The most complex level to study of ecology This is especially

a new field of study it has only recently become practical due to great advances

in satellite imagery of Earth global communication systems and breakdown of

national isolation which has allowed scientists from many countries to work

together and share results This is definitely he most interdisciplinary Ecological

Science it brings together scientific findings from many branches of science

including climatology oceanography meteorology soil science geology physics

chemistry and all the biological sciences

7 Evolutionary ecology It deals with the problems of niche segregation and speciation

8 Taxonomic ecology It is concerned with the ecology of different taxonomic groups of

living organisms and eventually includes following divisions of ecology microbial


ecology mammalian ecology insect ecology avian ecology parasitology human ecology

and so on

9 Applied ecology It deals with the application of ecological concepts to human need and

thus it includes following applications of ecology wild-life management range

management forestry conservation insect control epidemiology animal husbandry

aquaculture agriculture horticulture land use and pollution ecology

10 Production ecology It deals with the gross and net production of different

ecosystems like fresh water sea water agriculture horticulture etc and tries to do proper

management of these ecosystem so that maximum yield can be get from them

11 Physiological ecology The factors of environment have a direct bearing on the

functional aspects of organisms

12 Chemical ecology It concerns with the adaptations of animals of preferences of

particular organisms like insects to particular chemical substances

13 Space ecology It is a modern subdivision of ecology which is concerned with the

development of partially or completely regenerating ecosystems for supporting life of man

during long space flights or during extended exploration of extra-terrestrial environments

ScopeEcology is a multidisciplinary science and it includes not only the life sciences but

chemistry physics geology geography meteorology climatology hydrology palaeontology

archeology anthropology sociology and mathematics and statistics as well For explaining the

behaviour of an organism or biotic community in a given environment an ecologist has to

integrate the data which is obtained from many sources-morphology taxonomy genetics

physiology soil science climatology geology physics and chemistry

The scope of ecology is quite vast The study of ecological principles provides a

background for understanding the fundamental relationships of the natural community and also

the science dealing with particular environment such as forest soil ocean and inland waters

Many practical applications of this subject are found in agriculture horticulture forestry

limnology oceanography fishery biology biological survey pest control public

health toxicology pollution control conservation etc Ecological knowledge helps in


discovering new sources of food new unpolluting sources of energy and new methods of pest

control such as biological control which causes no environmental pollution

Some ecology related terminologyAbiotic factors Non-living ecological components of an ecosystem such water oxygen

sodium chloride nitrogen carbon dioxide etc and other physical and chemical influences such

as temperature light humidity pH etc

Biotic factors Living ecological components of an ecosystem such as producers

(chemosynthetic bacteria and photosynthetic green plants) consumers (heterotrophic animals

and decomposer organisms (bacteria fungi and other saprophytes)

Commensalism The living together of two species usually with benefit to one

Community A group of populations of plants and animals living together in a given place eg

the community of an oak forest a marsh a grassland a coral reef a desert etc

Competition Interaction occurs within interspecific or intraspecific population for utilizing

common resources that are in short supply (exploitation) or if the resources are not in short

supply for their survival or reproduction are known as competition

Consumers Organisms that ingest organic food (usually particulate) or other organisms

Dynamics In population ecology the study of reasons for changes in population size contrast

with statics

Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms

(biotic community) and non-living substances (abiotic environment) interacting to produce an

exchange of materials between the living and non-living parts

Habitat The natural abode of an organism including its total environment

Mutualism A interspecific relationship between two or more species in which both or all

benefit from the association and cannot live separately

Niche The ecological role or profession of an organism in its ecosystem its activities and

relationships to its community and total environment

Population Groups of individuals of single species a group of interacting individuals in a

definable space

Symbiosis The living together of two or more species


Ecosystem It is a spatial or organizational unit of biosphere which includes living organisms (biotic

community) and non-living substances (abiotic environment) interacting to produce an exchange

of materials between the living and non-living parts It may be as small as a puddle or as large as

the entire earth Further an ecosystem may be natural as a pond a lake a river an estuary an

ocean a forest etc or it may be man-made or artificial like an aquarium a dam a cropland a

garden an orchard a city and so on The term ecosystem was coined by a Ag Tansley (1935)-

its eco part means environment and the system part implies a complex of coordinated units

Structure of an ecosystem

From structural point of view all ecosystems consists of following four basic

components

1 Abiotic Substances

2 Biotic Substances factors

a Producers

b Consumers

c Reducers or Decomposers

Biotic Substances

These include basic inorganic and organic compounds of the environment or habitat of

the organism The inorganic compounds of an ecosystem are carbon dioxide water nitrogen

calcium phosphate all of which are involved in matter cycles The organic compounds of an

ecosystem are proteins carbohydrates lipids and amino acids all of which are synthesized by

the biota of an ecosystem and are reached to ecosystem as their wastes dead remains etc The

climate temperature light soil etc are other abiotic components of the ecosystem

Producers

Producers are autotrophic organisms like chemosynthetic and photosynthetic bacteria

blue green algae algae and all other green plants They are called ecosystem producers because

they capture energy from non-organic sources especially light and store some of the energy in

the form of chemical bonds for the later use


Consumers

They are heterotrophic organisms in the ecosystem which eat other living creatures

There are herbivorres which eat plants and carnivores which eat other animals They are also

called phagotrops or macroconsumers

Reducers or Decomposers

Reducers decomposers saprotrophs or microconsumers are heterotrophic organisms that

breakdown dead and waste matter Fungi and certain bacteria are the prime representatives of

this category

Examples of ecosystemA classic example of an ecosystem is a small lake or pond The abiotic or non-living parts

of a fresh water pond include the water dissolved oxygen carbon dioxide inorganic salts such

as phosphates nitrates and chlorides of sodium potassium and calcium and a multitude of

organic compounds such as amino acids humic acids etc The living part of the freshwater pond

can be subdivided according to the functions of the organisms ie what they contribute toward

keeping the ecosystem operating as a stable interacting whole In a freshwater pond there are

two types of producers the larger plants growing along the shore or floating in shallow water

and the microscopic floating plants most of which are algae that are distributed throughout the

water as deep as light will penetrate These tiny plants collectively referred to as phytoplankton

are usually not visible unless they are present in great abundance and give the water a greenish

tinge

The macroconsumers or phagotrophs of pond ecosystems include insects and insect

larvae Crustacea fish and perhaps some freshwater clams Primary consumers such as

zooplankton found near the surface of water and benthos are the plant eaters and secondary

consumers are the carnivores that eat the primary consumers

Types of ecosystemEllenberg (1973) has classified the world into a hierarchy of ecosystems Biosphere is

the largest and all-encompassing ecosystem Next lower level is mega-ecosystem such as

marine ecosystems (ie ecosystems of saline water of sea ocean and lake) limnic ecosystems

(ie ecosystems of fresh-water) semi-terrestrial ecosystems (ieecosystems of wet soil and

air) terrestrisl ecosystems (ieecosystems of aerated soil and air) and urban-industrial

ecosystems (man-made ecosystems like cropland city etc) The next-lower level is represented


by macro-ecosystems ( forests etc) within the mega ndashecosystem Meso-ecosystems (eg a

cold deciduous broad leaf foreat with its fauna) are considered as the basic units of thus scheme

Meso-ecosystems are sub divided into micro-ecosystems which depart with respect to a certain

component( a low land mountain or sub-alpine cold deciduous broad leaf forest with its fauna)

Nano-ecosystems are further small ecosystems which are spatially contained within larger

ecosystems and that show a certain individuality of their own

PopulationAll living organisms exist in groups of the same species or populations The word

population (L populus people) was originally referred to a group of people occupying a

particular space Thus a population can be defined as the tptal assemblage of individuals of the

same species occupying a particular space at a given time

Dispersion

Populations have a tendency to disperse or spread out in all directions until some barrier

is reached Accordingly population dispersion is the movement of individuals into or out of the

population area It takes three forms emigration-one way outward movement immigration-

one way inward movement and migration-periodic departure and return

Dispersion supplements natality and mortality in shaping population growth form and

density and also it plays a significant role in the distribution of plants and animals even to the

areas previously unoccupied by the members of the population Most types of population

dispersion occur due to a number of reasons such as for obtaining food avoiding predators

preventing overcrowding result of action of wind and water environmental factors as light and

temperature breeding behavior physiological reasons as secretion of some hormone or for

interchange of genetic material between populations

Emigration

Emigration under natural conditions occurs when there is overcrowding in the migratory

locust This is generally regarded as an adaptive behaviour that regulates the population on a

particular site and prevents overexploitation of the habitat Further it leads to occupation of new

areas elsewhere By dispersing into new localities there is opportunity gained for interbreeding

with other populations leading to more genetic geterozygosity and adaptability

Immigration


Immigration leads to a rise in population level causing an overpopulation which may

lead to an increase beyond the carrying capasity These immigrations result in increased

mortality among the immigrants or decreased reproductive capasity of the individuals Both

emigration and immigration are initiated by weather and other abiotic and biotic environmental

factors

Migration

Migration is a peculiar kind of population dispersion which involves the mass movement

of entire population This can occur only in mobile organism and best developed in insects like

the butterfly Dannaus plexippus and in the migratory dragonflies Libellula quadrimaculata and

Pantala flavescens

In most cases migration of population may occur for food shelter or reproduction

Types

There are two types of ecosystems that are of ecological interest-open and cybernetic

Open systems depends on an outside environment to provide inputs and accept outputs

The ecosystem is an open system for it receives energy from an outside source the sun fixes and

utilizes it and ultimately dissipates heat to space If the suns energy were to be cut off the

ecosystem would cease to function An open system can consist of a number of components or

parts called subsystem and each subsystem can consist of a number of elements

A cybernetic system which can also be an open system has some sort of feedback

system to make it self ndashregulating Most living systems possess cybernetic systems that can

function at various levels from the cell to the community but always functioning through

organisms-the difference being that in living systems the set point is not fixed

What is ecology

The scientific study of the interactions that determine the distribution and abundance of organisms

scientific study - process of observation and experimentation leading to the rejection of all but one hypothesis not the truth or fact but the best fitting explanation of all the observations

interactions - include both biotic and abiotic factors

distribution - where insects occur


abundance - a measurement of population size

from the point of view of agriculture studies of populations of insects and their interactions with the environment are often restricted to a unit we call an agroecosystem

- agroecosystems

may be extensive corn belt or wheat growing areas of the Great Plains of North America or

limited - isolated orchard consisting of a few acres plantedwith widely-spaced trees or a greenhouse

- agroecosystems regardless of size have some common characteristics including

(1) created and maintained by human effort

(2) agroecosystems often lack temporal continuity

(3) plant selection by humans

(4) in any particular system often reduced species diversity frequently a single species dominates

(5) uniform phenology

phenology defn the study of seasonal changes which give rise to the observed periodicity of biological phenomena

(6) addition of nutrients

(7) frequently occurring insect weed and disease outbreaks

Ecology (from the Greek oikos meaning house or dwelling and logos meaning discourse) is the study of the interactions of organisms with each other and their environment Always remember that Ecology is a SCIENCE not a sociopolitical movement (eg environmentalism) The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystemsThe ECOSYSTEM is all living communities (biotic) and their associated non-living (abiotic) environmental components in a defined area Examples in southern Florida Everglades - a shallow wetland or marsh Hammock - hardwood (ie flowering tree) forest on higher ground within the Everglades Pine rocklands ndash on higher ground maintained by fire which prevents hardwoodsfrom taking overCoral ReefEstuaryMangrove


Evolution by natural selection is driven by ecological interactions in these habitatsLevels of Ecological StudyORGANISMAL ECOLOGY - the study of individual organisms behavior physiologymorphology etc in response to environmental challengesPOPULATION ECOLOGY - the study of factors that affect and change the size andgenetic composition of populations of organismsCOMMUNITY ECOLOGY - the study of how community structure and organization arechanged by interactions among living organismsECOSYSTEM ECOLOGY - the study of entire ecosystems including the responses andchanges in the community in response to the abiotic components of the ecosystemThis field is concerned with such large-scale topics as energy and nutrient cyclingAbiotic Components of the BiosphereThe plant community of a particular region depends on the CLIMATE--the combinationof temperature water light and wind And the flora (plants) directly affects thecomposition of the fauna (animals)TEMPERATURE contributes to erosion amp creation of soil affects what animals and plants can survive in an area since different organismshave different tolerances for cold and heatWATER The chemical balance of living tissues is a challenge in terrestrial and freshwaterenvironments species that have secondarily returned (what does this mean HINT dolphins andwhales have secondarily returned to marine water) to marine environments faceosmotic challenges as the ocean is now saltier than when their ancestors left it important component in erosion amp creation of soilsSUNLIGHT intensity varies with location and time of year daily duration varies with location and time of year angle of incidence of the sun (seasonal changes) competition for light is an important selective factor in many environments and thishas driven selection of many species photosynthesis wavelengths primarily in the blue amp red regions of spectrumunderstory and underwater regions have varying levels of these wavelengthswith red light being lost first and blue light last Animals and plants react to lightdark cycles with behavioral changes (egCircadian rhythms)WIND contributes to erosion affects perceived temperature via evaporation amp convection affects desiccation rate affects growth form of plantsROCKSSOIL topography creates habitat mineral (inorganic nutrient) content of rock affects flora pH of rocksoil affects flora


substrate composition affects any water in contact with that substrateMAJOR ENVIRONMENTAL DISTURBANCES fire severe storms (hurricanes tornadoes etc) volcanic activity oh heck Comets tooA Wee Bit of ORGANISMAL ECOLOGYThe ability of an organism to survive the extremes of its environment determine itssurvival and reproduction This is the basis of natural selection The success ofindividuals in an ecosystem determines the structure of the population in thatecosystemAnimals can be categorized by their ability (or inability) to control their internalenvironment (salt balance water balance temperature etc) REGULATORS - organisms able to use metabolic means to regulate their internalenvironments in response to environmental changesExample 1 thermoregulation (temperature control)o Healthy mammals and birds are able to control their internal temperatures at avery constant levelExample 2 osmoregulation (salt balance)o Some species of fish can migrate from salt to freshwater habitats every year withtheir breeding cycle (theyre called anadromous fish) Other species can migrate fromfreshwater to marine habitats every year with their breeding cycle (theyre calledcatadromous fish) These fish can maintain constant salt balance in their tissues viatheir renal systems (kidneys and associated structures) even when their environmentsvary drastically in salinity CONFORMERS - organisms whose internal conditions are controlled primarily byenvironmental conditionsExample 1 thermoregulationo most insects cannot control their internal body temperature to any great degreeRather their bodies are usually the same temperature as the environmentExample 2 osmoregulationo Echinoderms (things like starfish sea urchins etc) entirely lacking an excretorysystem are strictly limited to marine environments and their tissues have the samesalinity as sea waterWe can also categorize animals based on (1) where they get their heat and (2) howthey regulate their body temperature ectotherm - obtains heat primarily from the environment (a conformer) endotherm - obtains heat primarily from metabolic reactions (a regulator) poikilotherm - temperature regulated primarily by environment (a conformer) homeotherm - temperature regulated by internal mechanisms (a regulator)There is a continuum of tolerances to various environmental challenges within andamong species Beyond certain levels of any given factor a lethal range exists(Consider this for our own species)Short-term responses to environmental changes are known as ADAPTATIONS Theseare governed by the internal control (homeostatic) mechanisms in the individual but thelimits are set by the EVOLUTIONARY HISTORY of that individual


Individual adaptations to change may includephysiological acclimationSome species are able to physiologically ACCLIMATE (gradually change theirtolerance levels) in a slowly changing environment but this ability too is controlled bygenes that have been selected over evolutionary timemorphological changeMorphology may change in response to environment (consider coat changes shapechanges of crustaceans to environment)behavioral adaptationBehavioral adaptations allow an animal to respond relatively quickly toenvironmental challengeEcosystem EcologyMost everyone has seen a FOOD WEBThe food web is made up of organisms at different levels of feeding known asTROPHIC LEVELS primary (1o)producers - organisms that can perform photosynthesis primary (1o)consumers - organisms that eat primary producers secondary (2o)consumers - organisms that eat primary consumers tertiary (3o)consumers - organisms that eat secondary consumers quaternary (4o)consumers - organisms that eat tertiary consumersand so onDECOMPOSERS are a special type of consumer that can eat dead organic matter(detritus carrion) and convert it back into its inorganic componentsWe also can categorize animals on the basis of the exact type of food they eat You allhave heard of carnivore - animal that eats meat herbivore - animal that eats plant matter omnivore - animal that eats a variety of things (plant and animal)But dont forget detritivore - eats dead organic matter (detritus) but does not decompose it insectivore - eats insects frugivore - eats fruitsInsert your own favorite vore hereThe Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystemswhich well cover in more detail later But for now were going to create our own FoodEcologyThe term ecology is derived from the Greek term ldquooikosrdquo meaning ldquohouserdquocombined with ldquologyrdquo meaning ldquothe science ofrdquo or ldquothe study ofrdquo Thus literallyecology is the study of earthrsquos household comprising of the plants animalsmicroorganisms and people that live together as interdependent components The termecology was coined by a German biologist Ernst Haekel (1869)Definition of EcologyEcology can be defined as the science of plants and animals in relation to theirenvironmentWebsterrsquos dictionary defines ecology as ldquototality of pattern of relation betweenorganisms and their environmentrdquo


Eugene P Odum defined ecology as ldquothe study of organisms at homerdquoInsect Ecology may be defined as the understanding of physiology andbehaviour of insects as affected by their environmentEcology related terminologyi Habitat is the place where the organism livesii Population denotes groups of individuals of any kind of organism Insectpopulations are groups of individuals set in a frame that is limited in time andspaceiii Community in the ecological sense includes all the populations of a givenarea Community can also be defined as interacting lsquowebrsquo of populationswhere individuals in a population feed upon and in turn are fed upon byindividuals of other populations (Fig 1)iv EcosystemEcosystem or ecological system is the functioning together of community andthe nonliving environment where continuous exchange of matter and energytakes placeIn other words ecosystem is the assemblage of elements communities andphysical environmentEcosystem is the ultimate unit for study in ecology as they are composed ofliving organisms and the nonliving environmentExamples of natural ecosystem Ponds lakes and forests ecosystem (Fig2)v Biosphere is the term used for all of the earthrsquos ecosystems functioningtogether on the global scaleAgroecosystem is largely created and maintained to satisfy human wants orneeds It is not a natural ecosystem but is man made Agroecosystem is the basic unitof pest management - a branch of applied ecologyA typical agroecosysyetm (Fig 4) is composed ofi more or less uniform crop-plant populationii weed communitiesiii animal communities (including insects)iv microbiotic communitiesv and the physical environment the react withUnique features of AgroecosystemDominated by plants selected by manNo species diversity and no intraspecific diversity Genetically uniformPhenological events like germination flowering occur simultaneouslyLack of temporal continuity - due to various agricultural operations carried outby man like ploughing weeding pesticide application etcPlants contain imported genetic materialNutrients are addedOutbreak of pests weeds and diseases occur frequentlyBalance of NatureBalance of Nature is defined as the natural tendency of plant and animalpopulation resulting from natural regulative processes in an undisturbed ecosystem(environment) to neither decline in numbers to extinction nor increase to indefinitedensity


In unmanaged ecosystems a state of balance exists or will be reached thatis species interact with each other and with their physical environment in such a waythat on average individuals are able only to replace themselves Each species in thecommunity achieves a certain status that becomes fixed for a period of time and isresistant to change which is termed as the balance of natureWhen man begins to manage creating new ecosystem (agroecosystem)where natural ecosystem existed previously the balance is altered The exceptionallystrong forces react in opposition to our imposed change toward a return to the originalsystem (eg outbreak of a pest is one of the forces) So insect pests are not ecologicalaberrations Their activities counter wants and needs of human populationsFactors that determine insect abundancei) Biotic potentialIt is the innate ability of the population to reproduce and survive It dependson the inherited properties of the insect ie reproduction and survival Potentialnatality is the reproductive rate of the individuals in an optimal environmentSurvival rate depends on the feeding habits and protection to young ones (egViviparity) Generally insects with high reproductive rate tend to have low survivalrate and vice versaInsect pests with high reproductive rate and low survival rate are called rstrategists named after the statistical parameter r the symbol for growth ratecoefficient Such pests succeed because of sheer numbers Eg AphidsK strategists reproduce slowly but effectively compete for environmentalresources and so their survival rate is high (K letter denotes flattened portion ofgrowth curve) eg Codling moth of appleBirth rate or natality is measured as the total number of eggs laid per femaleper unit time Factors determining birth rate are fecundity fertility and sex ratioDeath rate or mortality denotes the number of insects dying over a periodEnvironmental resistance is the physical and biological restraints thatprevent a species from realizing its Biotic potential Environmental resistance may beof 2 types1 Biotic factors - includesa) Competition (interspecific and intraspecific)b) Natural enemies (predators parasites and pathogens)2 Abiotic factors -a) Temperatureb) Lightc) Moisture and waterd) Substratum and mediumBIORESOURCES IN ECOSYSTEMEcosystem comprises of biological communities and non-living environmenteg Agro ecosystem pond ecosystem etc) Bioresources refers to the biodiversityof various organisms living in that ecosystemeg The different pests of cotton its natural enemies hyperparasitoids microbes etcare referred to the bioresources in cotton ecosystemThe ecosystem should have more bioresources Such ecosystem will bemore stable Insecticides will deplete the bioresources in ecosystem and make it less


stable and prone to pest outbreakNatural control will be high when bioresources (eg Parasitoids and

Predators) are more

Population dynamics and role of biotic factorsAttributes of a populationi Density Population size per unit areaii Birth rate (Natality) Rate at which new individuals are added to thepopulation by reproductioniii Death rate (Mortality) The rate at which individuals are lost by deathiv Dispersal The rate at which individuals immigrate into and emigrate out ofthe populationv Dispersion the way in which individuals are distributed in space It may be of3 typesa) Random distributionb) Uniform distributionc) Clumped distributionvi Age distribution the population of individuals of different ages in the groupvii Genetic characteristics adaptiveness reproductive fitness persistenceviii Population growth form the way in which population changes grows as aresult of natality mortality and dispersalPopulation dynamicsPopulations grow in two contrasting ways They arei J- shaped growth form (Fig 1a)ii S- Shaped or sigmoid growth form (Fig 1b)N KDensity DensityTime TimeFig 1a J- shaped growth form Fig 1b S - shaped growth formIn the J - shaped growth form the population density increases in exponentialor geometric fashion for example 2481632 hellip and so on until the population runsout of some resource or encounters some limitation (limit N Fig 1a) Growth thencomes to a more or less abrupt halt and density declines rapidly Populations with thiskind of growth form are unstable Their reproductive rate is high and survival rate isless and so they are r strategists Factors other than density regulates thepopulation(eg Aphids)In the S-shaped growth pattern (Fig 2) the rate of increase of density decreasesas the population increases and levels off at an upper asymptote level K called thecarrying capacity or maximum sustainable density Their reproductive rate is less andsurvival rate is more So they are K strategists This pattern has more stability sincethe population regulates itself(eg Hymenopterans)The population growth rate or change is worked out using the formulaNt = N0e(b-d)t - Et + It


Where Nt = number at the end of a short time periodN0 = number at the beginning of a short time periode = base of natural logarithm = 27183b= birth rated= death ratet= time periodE= emigrationI = immigrationLife table Life tables are tabular statements showing the number of insects dyingover a period of time and accounting for their deathsFactors influencing population growtha) Biotic factors or density dependent factorsb) Abiotic factors or density independent factorsBiotic factors1) Competition For at least part of the lifetime the members of an insect species arelikely to be competing with one another or with members of another species forlimited resources like food mates suitable site for oviposition or pupation Suchcompetition operates whenever the population is increasing and the resources arelimiteda) Intraspecific competition When members of population of the samespecies compete for resources we call it intraspecific competition Examples are asfollows1051419 Cannibalism in American bollworm larvae1051419 Cannibalism in later stage grubs of Chrysopid1051419 Crowding in aphids result in alate (winged) form for migration1051419 Reduction in fecundity (egg laying) in rice weevil Sitophilus oryzae duringovercrowding1051419 Crowding in honeybees leads to swarmingb) Interspecific competition This is the competition occurring betweenmembers of two or more species Two or more competing species with identicalrequirements cannot coexist in a same place for a long time The elimination ofone species by another as a result of interspecific competition has come to beknown as the competitive exclusion principle or Gausersquos principle1051419 For example when flour beetles Tribolium castaneum and Tribolium confusumwere grown in the same jar of flour one species eliminates the other Underhigh temperature and RH conditions T castaneum eliminates Tconfusum andvice versa under low temperature and RH conditions1051419 Accidental introduction of oriental fruit fly Dacus dorsalis into Hawaieliminated Mediterranean fruit fly Ceratitis capitata2) Predators and ParasitesPredators Predators are free living organisms that feed on other animalstheir prey devouring them completely and rapidly1051419 Predators may attack immatures and adults1051419 More than one individual of prey required for predator to reach maturity1051419 Major insect predators are birds fish amphibians reptiles mammals andarthropods


Parasites An organism that is dependent for some essential metabolic factor onanother throughout its all life stages which is always larger than itself1051419 A parasite weakens or kills the host while feeding1051419 Many parasites on asingle host1051419 Requires only one part of one host to reach maturityEg Virus fungi bacteria protozoa nematodes and other arthropodsParasitoid An insect parasite of an arthropod that is parasitic in its immature stagekilling the host in the process of development and adults are free livingInteractions between predator and prey are different from the parasite host relationshipin that the predator and prey maintain equilibrium more dynamically than the parasite and its hostThe parasites I n general when the rate of parasitism is high cause death and result in elimination

of hosts But the predator never eliminates the prey completely

1) density - insects per unit area

2) dispersion - spatial arrangement of the insects in the landscape

a regularuniform b random c clumpedaggregated

3) dispersal - not trivial movements but immigration into an area or emigration from an area

long distance

eg Canadian prairies - diamondback moth dont usually complete development in our climate recently they have been shown to overwinter here

short distance (on a more local level)

(i) nearby crops(ii) nearby alternate hosts - aphids woody shrubs and herbaceous plant

4) age distribution - proportion of individuals in different age groups at any given time eg Codling moth adult flight

univoltine - single generation in a year (many pest insect species especially in cooler regions)

multivoltine - two or more generations in a year the number of generations is dependent upon the developmental time requirements and adequate environmental conditions eg heat

- whether a species is multivoltine or univoltine can depend upon genetic program or the environment e g codling moth versus forest tent caterpillar FTC

- codling moth there are one to three generations per year as conditions in a given location permit there is one generation per year regardless of conditions


5) natality - birth rates

6) mortality - death rates - mortality is caused by numerous factors

ABIOTIC BIOTIC1) temperature 1) predators2) moisture 2) parasites3) weather 3) disease4) climate 4) competition

ABIOTIC

- in general insects which are in their natural habitats are well adapted - distribution of host plants (characteristics of an agroecosystem) may alter the natural distribution so that abiotic factors are more important

- insects are found at the limits of their range perspective of abiotic factors

- will they adapt and extend range If they do will they become a problem - occasionally unusual weather conditions may have significant impact on insect abundance - or given sufficient knowledge of abiotic factors one can perturb the system so as to reduce the survivorship of an insect

e g turn over the soil for insects which overwinter as pupae in the soil

1) temperature - outside the limits or thresholds temperature too much or little heat can have deleterious effects

2) moisture - moisture conditions may significantly infuence insect survival

- grasshopper eggs require specific soil moisture conditions if moisture conditions are suboptimal egg survivorship decreases - thus if soil moisture levels remain optimal for several years grasshopper populations can increase- complicated by the observation that moisture levels that are optimal for grasshopper egg laying may be optimal for natural enemies as well

3) weather - winds can transport sufficient numbers of insects to cause damage in areas where these insects would not normally survive

- heavy rains can dislodge young insects from foliage and these are subsequently destroyed

4) climate - interaction of the previous factors and others


- described insects which reach Canada but never become permanently established- some early attempts at biological control failed because of a failure to understand the effects of climate of insects

e g difficult to establish

a) lab and short term field results indicated that a predator had good control potentialb) under natural conditions differential effects of the climatic conditions led to asynchrony - pest wasnt available when predator active

BIOTIC

1) predators 2) parasites and 3) disease (natural enemies)

- in general the greater the diversity and abundance of natural enemies the greater the capacity to reduce pest population densities

- this is a feedback system and when pest numbers are low the abundance of natural enemies is frequently also low

- under natural conditions increases in population densities of natural enemies lag behind that of their hosts

4) competition

i interspecific -different species competing for the same resources

eg cone moths -distort cone - kills other insects in the conerarely of value for agriculture

ii intraspecific - as population increases competition for remaining resources increases oviposition sites food overwintering sites

eg Pupation sites for overwintering codling moth

clean up debris prepare trap sites - banding trees with cloth

-there are many other factors which may contribute to insect mortality but these should be examined on a case by case basis

-use information (ecological inputs) to develop management model (system where data from many sources is integrated in a control strategy)


(1) Exponential Growth Model ndash the rate of expansion of a population under ideal conditions in which the population multiplies by a constant factor during constant time intervals (generation time) The constant factor for bacteria is 2 because each parent cell divides to produce 2 daughter cells The generation time for the bacteria in the graph below is 20 minutes With each passing generation the population size increases by an exponent of the number 2 ndash hence the name Exponential Growth Model This Growth model occurs under ideal conditions and foe only short bursts of time Eventually limited resource become exhausted andor disease spread more and more rapidly In nature we usually only see this type of growth when organisms are confronted with a new or under-exploited environment

(2) Logistic Growth Model ndash In nature a population may grow exponentially for a short while but eventually one or more environmental factors will limit its growth ndash at which the population will stops increasing or crashes Environmental factors that restrict growth are referred to as population-limiting factors Logistic Growth is characterized by carrying capacity the highest number of individuals which an environment can support remember resources are limited

Notice that with Logistic Growth a population tends to grow rapidly when resources are abundant but growth starts to rapidly slow and even come to a halt as resources become depleted


Resources can include food water light oxygen mates shelter breeding sites nesting space and so on

Regulation of Population Growth ndash There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent

(1) Density-Dependent ndash these are factors that change in intensity as a function of population density (ie the more individuals crammed into a finite space with finite resources the more severe the density-Dependent Limiting Factors Includes Intra-specific Competition ndash members of the same species and same population compete for limited resources This is a major factor in population dynamics As you can imagine this type of struggle for resource does in fact usually lead to survival of the fittest Those individuals more capable of acquiring resources will usually survive better and leave more offspring (2) Density-Independent ndash these are limiting factors that are more or less random in that they donrsquot act as a function of population density However these limiting factors can have extreme effects upon population growth These factors include floods drought lighting fires volcanic eruptions hellip

EcologyStudy of the interaction between organisms and their environment environment composed of abiotic and biotic factors

Abiotic component Soil altitude climate (temperature humidity wind etc) latitude otherBiotic component Predators prey parasites competitors others

Major Areas of Ecology

Population Ecology Study of population growth and factors that affect growth

Community Ecology Study of interactions among species ecological succession

Ecosystems and the Biosphere Study of cycling of materials and energy through ecosystems

Population Ecology Study of distribution density numbers of individuals and structure (gender age) rates of natality and mortality factors that affect growth

Population group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time

Characteristics of PopulationsDensity - number of individualsper unit area (eg per acre or hectare) or unit volume (eg in a column of water)Spacing - dispersion

Density and numbers


Counting individuals to determine density and population size


Conventionally ecology has been defined variously by different classical and modern

ecologists with different view of points Quite oddly no universally accepted definition of

ecology has been formulated by any ecologists so far and for the better understanding of scope

limitations purpose and mode of study of different ecological phenomena one has to go through

following chronologically arranged definitions of ecology

Ernst Haeckel (1869) defined ecology as the body of knowledge concerning the economy of

nature- the investigation of the total relations of animal to its inorganic and organic

environment

British ecologist Charles Elton (1927) defined ecology as the scientific natural history

concerned with the sociology and economics of animals

Taylor (1936) preferred to define ecology as the science of the relations of all organisms to all

their environments

A much broader definition of ecology of Allee et al (1949) considered ecology as the science

of inter-relation between living organisms and their environment including both the physical

and biotic environments and emphasizing inter-species as well as intra-species relations

SC Kendeigh (1961) defined ecology as the study of animals and plants in their relation to

each other and to their environment

Andrewartha (1961) defined ecology as the scientific study of the distribution and abundance

of animals

Odum (1963) defined ecology as the study of the structure and function of nature ecosystem

approach

GAPetrides (1968) defined ecology as the study of environmental interactions which control

the welfare of living things regulating their distribution abundance production and evolution

Krebs (1972) defined ecology as the scientific study of the interactions that determine the

distribution and abundance of organisms

Southwick (1976) defined ecology as the scientific study of the relationships of living

organisms with each other and with their environments He further elaborates his definition of

ecology by saying that it is the science of biological interactions among individuals

populations and communities and it is also the science of ecosystems-the inter-relations of

biotic communities with their non-living environments





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