Ecology & Pest Management

Ecological Aspects


  • Ecology: Study of complex interactions between living organisms and nonliving environment in a particular place.
  • Ecosystem: The complex interacting system between living and nonliving factors is called as ecosystem.
  • Existence and abundance of a species is determined by biotic and abiotic factors, besides the genetic makeup of the species.
  • Biotic factors: Living factors like competition, predators, parasitoids, etc.
  • Abiotic factors: Non living factors like temperature, RH, photoperiod, etc.
Important components responsible for population growth:
  • Physical environment (abiotic factors), food, space, population itself, other species.
    • All these components act on the population through the pathways of natality, mortality and dispersal.
Characteristics of a population:
  • Density, natality, mortality, dispersal, dispersion, age distribution, population growth
  • Density: Number of individuals per unit area or space occupied.
    • Crude density: Number of individuals per unit of total space.
    • Ecological density: Number of individuals per unit of habitat space i.e. space occupied by the population.
  • Natality: Number of new individuals produced per unit time i.e. birth rate.
    • Absolute natality/ physiological natality: Theoretical maximum number of individuals that can be produced under most ideal conditions.
    • Ecological natality: Number of individuals that can be produced under specific environmental conditions.
  • Mortality: Number of individuals dying in a given population in a given period of time.
    • Minimum mortality: Mortality of individuals under most ideal or non limiting conditions.
    • Ecological mortality: Mortality of a population under specific environmental conditions.
Survivorship curves:
  • Convex curve: High survival throughout most of the life span, until the near end of the life span. (common in mammals and social insects like honey bees)
  • Concave curve: Mortality rate during early age is high followed by a period of much lower and relatively constant losses. (Found in parasites, grasshoppers, frogs, etc)
  • Constant curve: This curve implies a constant rate of survival independent of age. Probably no population in reality posses a constant survival rate throughout the whole life. A modification of this curve, however, may be present in insects like butterflies.
Dispersal: The movement of individuals in to or out of the population
  • Immigration: Movement in to the population.
  • Emigration: Movement out of the population.
  • Migration: Mass movement of the entire population. Such movements are generally seasonal or periodical.
Role of dispersal in population dynamics:
  • Helps in shaping the population growth form by supplementing mortality and natality
  • New or unpopulated areas are colonized.
  • Helps to introduce genetic variability through interchange between populations
  • Leads to an increase in the range of species
Dispersion: Distribution of individuals within a population at a particular time.
  • Random (Poisson): Mean = Variance
  • Uniform (+ve binomial): Mean > Variance
  • Clumped (-ve binomial): Mean < Variance
Age distribution: Relative proportion of individuals of different age groups of a population is called age distribution or age structure.
  • More young individuals: population is expanding
  • More older individuals : population is declining
  • Even distribution of various age groups means stationary population

Population growth:
Exponential growth model:

Nt= N0ermt
Where
Nt= Number of individuals at time t
N0 = Number of individuals at time zero
e = base of natural log
rm = Innate capacity of increase
t = Time period
Population growth occurs due to the interplay of biotic potential and environmental resistance
  • Biotic potential: Inherent property of individual to reproduce and survive i.e. to increase in number
  • Environmental resistance: It is the sum total of environment’s limiting factors that prevent the biotic potential from being realized
Logisic growth model:
dN/dt = rN (K-N)/K
dN/dt – Rate of population growth
r – Intrinsic rate of increase
N – Population number
K – Carrying capacity

FACTORS INFLUENCING PEST POPULATIONS:
  • Abiotic factors (Temperature, humidity, light)
  • Biotic factors (Food, predators, parasitoids, pathogens)
Temperature: Affects the following parameters of individuals of population
  • Endocrine system
  • Growth
  • Development
  • Reproduction
Humidity:
  • Normal development and feeding activity.
  • By encouraging diseases.
  • Excessive body moisture during winter may reduce its capabilities to withstand low temperatures.
Light:
  • Orientation, rhythmic behaviour, bioluminescence, periodicities of occurrence and periods of inactivity.
  • Light acts as stimulus for insects to synchronize and regulate their life cycles with change in seasons.
  • Influences the motor activity rhythm of insects such as locomotion, feeding, adult emergence, mating, oviposition, and also moulting and growth in some species.
Biotic factors:
  • Food:
    • Food quality and quantity affects growth, development, survival, longevity, reproduction, distribution, etc.
    • When the food is in short supply there is intraspecific or interspecific competition.
    • Competition acts in density dependent manner.
    • Food supply may be affected by many factors
  • Natural enemies: Predators, parasitoids and entomopathogens like bacteria, fungi, viruses, nematodes, rickettsiae, etc.
  • Natural enemies act negatively on insect populations.
  • Influence is variable because their own populations are influenced by various environmental factors.
  • Predators generally respond to increase in pests population through:
    • Numerical response (By increasing their number)
    • Functional response (By increasing the consumption).
Last modified: Saturday, 3 March 2012, 9:32 AM