Introduction to Environmental Science

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Introduction to Environmental Science

• Dr Benny K. K. Chan and Dr Billy C.H. Hau
• Dept. Ecology Biodiversity,
• HKU

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Ecology is the basic science in environmental
life sciences
Sustainable development Biodiversity Conservation
biology Restoration ecology Ecotoxicology Landscap
e ecology Environmental economics Environmental
impact assessment
Ecotourism Forestry Public policies
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What is Ecology?
The study of the interactions between organisms
and their environment. Ernest Haeckel, 1869
The study of the relationships, distribution, and
abundance of organisms, or groups of organisms,
in an environment. S.I.
Dodson, 1998
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We can study ecology at 3 levels of concern
Individuals - living organisms, fundamental units
of populations and communities
Populations - group of individuals of a species
Communities - an assemblages of species
populations occurring together in space and time
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Aims of this lecture

• How individuals, populations and community
  interacts with the environment
• Ecosystem trophic levels and energy transfer

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Learning outcomes

• At the end of this section, you should be able to
  understand
• Factors affecting the survival of individuals in
  the environment natural selection and
  adaptation.
• Structure of a population and factors governing
  the population structure.
• Community ecology interactions between
  individuals/populations/assemblages.
• Ecosystem Trophic levels and energy flows

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Individuals

• The individuals of a species are not identical
  (variations in genotypes which are
  inheritable).
• Some of the genotypes will be more favorable in
  living in certain environment

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Natural Selection Charles Darwin 1859

• Environmental condition that favours some
  individuals have certain genotypes to survive
  better in certain habitats.
• Survival of fitness proposed by Spencer
• Fitness contributions of individuals to the
  future population
• Those survive are healthy individual that fit
  their environment and can transfer their gene
  into the population
• Different populations may have different
  genotypes.

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Adaptation

• Adaptation characteristics of organisms evolved
  as a result of natural selection to make it
  closely match with its environment
• Morphological and physiological adaptations

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Population

• Population a group of organisms of the same
  species living together in a location at the same
  time.
• Population Ecology - the study of how and why
  populations change in abundance in space and time.

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Population structure
Immigration
Birth
Gains
Population
Loss
Death
Emigration
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Factors affecting the structure of population

• Birth and death of organisms survivorship curve
• Three types of survivorships
• Type I, II and III

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Survivorship curve
Refer to Fig. 4.8 in Chapman and Reiss 1999
full references are in the last slide
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r selected populations type III

• r intrinsic rate of growth
• Adapted to reproduce rapidly
• Produce a large number but small sized offspring
• High mortality of individuals
• Live in environment which are unpredictable with
  time
• e.g. rocky shores invertebrates

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K selected populations type II

• K carrying capacity of the environment
• Reproduce slowly
• With small number but large sized offspring
• Low mortality of juveniles
• Live in stable environment
• e.g. mammals

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Interactions between populations

• Competition
• Predation
• Parasitism
• Mutualism

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Ecology Population
Competition The interaction between individuals,
brought about by a shared requirements for a
resources in limited supply, and leading to a
reduction in the survivorship, growth and/or
reproduction of the competing individuals
concerned
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Intraspecific competition Competition between
individuals of the same species
Interspecific competition Competition between
individuals of different species
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Ecology Population
Intraspecific competition

• Features
• lead to decreases in survivorship/ fecundity
• competing individuals are in essence equivalent
• More competitors, greater effect on individuals
  (density dependent)

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Refer to Fig. 6.10 in Begon et al. 1990 full
references are in the last slide
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Ecology Population
Interspecific competition

• Features
• competing species exclude one another from
  particular habitats so that they do not co-exist
• exclusion depends on initial densities
• Competing species may co-exist by utilizing the
  habitat in slightly different ways

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Refer to Fig. 7.3 in Begon et al. 1990 full
references are in the last slide
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Ecology Population

• The Competitive Exclusion Principle
• If 2 competing species coexist in a stable
  environment, they do so as a result of niche
  differentiation.
• If no niche differentiation, or it is precluded
  by the habitat, then one species will eliminate
  or exclude the other

Niche is the combination of conditions and
resources that allow the species to maintain a
viable population
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Ecology Population
Predation The consumption of one organism (the
prey) by another organism (the predator), in
which the prey is alive when the predation first
attack it.
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Ecology Population

• Effect on predator population depends on the
  generation time of the predator
• predators with short life span (e.g. insects) can
  keep track with the fluctuations in the abundance
  of prey
• predators with long life span (e.g. mammals) take
  a longer period to respond to changes in prey
  abundance

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Mutualisms

• Both species involved gained benefits
• Example the sponge and sponge crab
• Sponge gain the benefits of movement higher
  chance of finding food
• Crab gain protection from predation

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Community

• Co-existence of species in space and time
• Species composition in a community seldom in a
  stable status
• Disturbance physical and biological factors

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Effect of predators on community structure

• Keystone species
• The starfish (Pisaster) prey on a variety of
  preys including barnacles, limpets, chitons and
  mussels.

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Keystone species expt.

• Exclusion experiment

Refer to Fig. 21.3 in Begon et al. 1990 full
references are in the last slide
Experimental removal of starfish lead to a huge
increase of mussels which overgrowth other
species reduction of species richness
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Effects of predator density

• Low Medium High

Refer to Fig. 21.1 in Begon et al. 1990 full
references are in the last slide
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Trophic levels and energy flows

• Feeding relationship between organisms
• Modes of nutrition
• Autotrophs - producers
• Heterotrophs - consumers
• carnivores
• herbivores (granivores frugivores grazers
  browsers)
• omnivores
• decomposers
• detritivores
• Parasites

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Food chain

• Refer to Fig. 21.5 in Chapman and Reiss 1999
  full references are in the last slide

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Food web in oceans
Refer to Fig. 11.8 in Chapman and Reiss 1999
full references are in the last slide
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How do we know the patterns of food chain?

• Examine the gut contents of the consumers
• Conduct stable isotope ratio studies.
• Different food items have different isotope
  ratio (signature)
• Consumer digesting the food will absorbed those
  isotope ration into the tissue.
• Analysis of the stable-isotope into tissue will
  reflect the food items taken.

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Pyramid of numbers generalizations and
exceptions

• Refer to Fig. 11.9 in Chapman and Reiss 1999
  full references are in the last slide

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Refer to Fig. 11.10a, b in Chapman and Reiss 1999
full references are in the last slide
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Productivity

• Primary production by autotrophs
• Gross primary productivity total amount of dry
  matters made by a plant in photosynthesis.
• Respiration also used up the energy produced in
  photosynthesis.
• Net primary productivity Gross primary
  productivity - respiration

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Productivity in terrestrial system

• Refer to Table 12.1 in Chapman and Reiss 1999
  full references are in the last slide

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Factors affecting primary productivity

• Nutrients, water availability, solar radiation
• More importantly, transpiration

Refer to Fig. 12.2 in Chapman and Reiss 1999
full references are in the last slide
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Primary productivity and biodiversity
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Primary productivity in aquatic environment
Refer to Table 12.2 in Chapman and Reiss 1999
full references are in the last slide

• Limiting factors nutrients input

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Energy flow in food web
Refer to Fig. 12.9 in Chapman and Reiss 1999
full references are in the last slide
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Summary
Individuals
Populations
Environment
Trophic relationships
Communities
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References

• Begon M., Harper J. L. and Townsend C. R. (1990).
  Ecology Individuals, Populations and
  Communities. Blackwell Scientific Publications.
• Chapman J. L. and Reiss M. J. (1999). Ecology
  Principles and Applications. Cambridge
  University Press

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Learning outcomes

• At the end of this section, you should be able to
  understand
• Factors affecting the survival of individuals in
  the environment natural selection and
  adaptation.
• Structure of a population and factors governing
  the population structure.
• Community ecology interactions between
  individuals/populations/assemblages.
• Ecosystem Trophic levels and energy flows