R. R. Thaman

1
ISLAND BIOGEOGRAPHY

• R. R. Thaman
• GE301/407 Applied/Advanced Island Biogeography
  and Ethnobiology

2
ISLAND BIOGEOGRAPHY

• The Study of the distribution, composition and
  abundance (including absence) of island
  biodiversity
• The study of island ecosystems, species,
  taxonomic and genetic diversity.

3
ISLAND BIOGEOGRAPHY

• Attempts to explain the reasons/factors
  responsible for these patterns and the nature of
  island biotas (flora, fauna and microbiota).
• Attempts to explain Richness and Poverty of
  species.

4
ISLAND BIOGEOGRAPHY

• Also interested in the impact of human societies
  on island biogeography
• ETHNOBIODIVERSITY (the study of the knowledge,
  uses, management systems, beliefs and language
  that island cultures have for their biodiversity)
  . . .
• Because island cultures have co-evolved with
  their biodiversity.
•  

5
ISLAND BIOGEOGRAPHY

• Islands as unique ecological laboratories, where
  simple ecosystems can be studied more easily than
  continental ecosystems.
• Islands as laboratories for the study of
  evolution and co-evolution (HIGH ENDEMISM).
• The theory of evolution was based on Charles
  Darwins study of the island biota of the
  Galapagos Islands and Wallaces study of the
  islands of Indonesia (MALESIA) and the Indian
  Ocean.

6
Island Arks largely responsible for Darwin and
Wallace challenging the biblical ark of
Christendom and the formulation of their theory
on the evolution of new life forms
7

• . . . it is not too much to say that when we
  have mastered the difficulties presented by the
  peculiarities of island life we shall find it
  comparatively easy to deal with the more complex
  and less clearly defined problems of continental
  distribution . . .

Alfred Russel Wallace Island Life (1902 242 in
Whittaker 1998)
8
Equilibrium Theory of IBG

• Two eminent ecologists, the late Robert MacArthur
  of Princeton University and E. 0. Wilson of
  Harvard, developed a theory of "island
  biogeography" to explain uneven distributions in
  the RICHNESS (numbers) of species of a given taxa
  on islands.

9
Equilibrium Theory of IBG

• They proposed that the maximum number of species
  on any island (EQUILIBRIAL NUMBER) reflects a
  balance between
• IMMIGRATION the rate at which new species
  colonize it (HIGH IN THE BEGINNING), and,
• EXTINCTION the rate at which populations of
  established species become extinct (LOW IN THE
  BEGINNING).

10
Theory of IBG

• EXAMPLE If a new volcanic island were to rise
  out of the ocean off the coast of a mainland
  inhabited by 100 species of birds, some birds
  would begin to immigrate across the gap and
  establish populations on the empty island.
• After a while some would begin to become extinct
• REAL CASE Catastrophic eruption of Krakatoa Is.
  between Java and Sumatra (Indonesia) in 1883.

11
Theory of IBG

• The rate at which these immigrant species could
  become established, however, would decline over
  time because
• Each species that successfully invades the island
  will reduce by one the pool of possible future
  invaders
• In other words, the same 100 species continue to
  live on the mainland, but those which have
  already become residents of the island can no
  longer be considered to be potential invaders.

12
Theory of IBG

• The rate at which additional species will
  establish populations will be high when the
  island is relatively empty, and the rate at which
  resident populations go extinct will be high when
  the island is relatively full.
• Thus, there must be a point between 0 and 100
  species (the number on the mainland) where the
  two rates are equal -- where new input from
  immigration balances output from extinction.

13
Theory of IBG

• Equally, the extinction on the island would be
  related to the number that have become residents.
• When an island is nearly empty, the extinction
  rate is low because few species are available to
  compete with each other or be killed off by
  extreme events and become extinct.
• And since the resources of an island are limited,
  as the number of resident species increases, the
  smaller and more prone to extinction the
  individual populations of each species are likely
  to become.

14
Theory of IBG

• That equilibrium number of species would be
  expected to remain constant as long as the
  factors determining the two rates did not change.
• But the exact species present should change
  continuously as some species go extinct and
  others invade (including some that have
  previously gone extinct), so that there is a
  steady turnover (SPECIES TURNOVER) in the
  composition of the fauna.

15
Theory of IBG

• This is the essence of the MacArthur-Wilson
  equilibrium theory of island biogeography.
• How well does it explain what we actually observe
  in nature?

16
RECOLONIZATION OF KRAKATAU (Krakatoa)

• One famous "test" of the theory was provided in
  1883 by a catastrophic volcanic explosion that
  devastated the island of Krakatoa, located
  between the islands of Sumatra and Java.
• The flora and fauna of its remnant and of two
  adjacent islands were completely exterminated,
  yet within 25 years (1908) thirteen species of
  birds had recolonized what was left of the
  island.
• By 1919-21 twenty-eight bird species were
  present, and by 1932-34, twenty-nine.
• Between the explosion and 1934, thirty-four
  species actually became established, but five of
  them went extinct.

17
Theory of IBG

• By 1951-52 thirty-three species were present, and
  by 1984-85, thirty-five species.
• During the half century (1934-1985), a further
  fourteen species had become established, and
  eight had become extinct.

18
Theory of IBG

• As the theory predicted, the rate of increase
  declined as more and more species colonized the
  island.
• In addition, as equilibrium was approached there
  was some species turnover. The number of bird
  species remained roughly the same while the
  species COMPOSITION gradually changed.

19
Theory of IBG

• The theory predicts other things, too.
• For instance, everything else being equal,
  distant islands will have lower immigration rates
  than those close to a mainland, and equilibrium
  will occur with fewer species on distant islands.
• Close islands will have high immigration rates
  and support more species AT EQUILIBIRUM.

20
Theory of IBG

• By similar reasoning, large islands, with their
  lower extinction rates, will have more species
  than small ones -- again everything else being
  equal (which it frequently is not, for larger
  islands often have a greater variety of habitats
  and more species for that reason).

21
(No Transcript)
22
Characteristics of Island Biotas/Biodiversity

• Island biotas/ecosystems are often disharmonic
  (missing major types or groups of
  organisms/missing major taxa).
• Large predators (carnivores)
• Large herbivores
• Ants (e.g., Hawaii had no native ants)
• Birds of prey/raptors (hawks, eagles, etc.)
• Aggressive weeds
• Disease organisms (e.g., influenza, whooping
  cough and measles, which decimated Pacific
  Islands human populations and avian malaria that
  devastated HawaiIs endemic birds

23
Characteristics of Island Biotas/Biodiversity

• They have smaller population sizes than
  continental ecosystems
• Have limited genetic diversity within the
  population because they have descended from a
  single or limited number of founder species/the
  founder population (FOUNDER EFFECT)
• these small populations are more prone to
  extinction (total extinction) and extirpation
  (local extinction).

24
Characteristics of Island Biotas/Biodiversity

• There is a high degree of endemism ( of unique
  plants and animals that are found nowhere else),
  because of the process of adaptive radiation and
  ecological release into unexploited or
  inadequately filled HABITATS and NICHES.
• Many islands are considered to be global
  BIODIVERSITY HOTSPOTS

25
Characteristics of Island Biotas/Biodiversity

• There is also a very low level, or absence, of
  endemism ( of unique plants and animals that are
  found nowhere else) on atolls and small low-lying
  islands, which are usually populated with
  ubiquitous pantropical or pan-Pacific plants
  and animals.
• Many are considered to be global BIODIVERSITY
  COOLSPOTS

26
Characteristics of Island Biotas/Biodiversity

• Island ecosystems are usually very fragile
  because they have evolved in a state of less
  competition, usually because of disharmony and
  because they have small populations (total number
  of individuals of a given species) and limited
  genetic diversity within populations.

27
Factors Controlling Island Biodiversity

• Dispersability of plants, animals (vertebrates
  and invertebrates) and microorganisms.
• Distance of island (SPECIES-DISTANCE EFFECT)from
  source areas and centers of diversity
• Richness of the source area of colonizing
  organisms.

28
Factors Controlling Island Biodiversity

• Size of island (SPECIES-AREA EFFECT) leads to
  greater chance of colonization, greater habitat
  diversity, more space, greater protection from
  coastal marine influences, greater habitat and
  microhabitat diversity and higher population
  numbers
• Elevation/topography greater habitat and
  climatic diversity

29
Factors Controlling Island Biodiversity

• Island type or substrate continental, plate
  boundary volcanic, hotspot volcanic, raised
  limestone, low-lying atolls and limestone islands
  and sand cays
• Geologic age Ancient continental and volcanic
  islands, ancient limestone islands and recent
  volcanic islands.

30
Factors Controlling Island Biodiversity

• Climate (moisture, temperature, latitude/day
  length, winds, etc.)
• Frequency and severity of extreme events
  (tropical cyclones, droughts, floods, tsunamis,
  volcanic eruptions, disease outbreaks)

31
Factors Controlling Island Biodiversity

• Nature of ocean currents (e.g., for dispersal of
  plankton and planktonic larval stages of marine
  organismsceanic
• Wind patterns (e.g., for the dispersal of birds,
  bats, insects and atmospheric plankton (very
  small insects and microorganisms).

32
Factors Controlling Island Biodiversity

• IMPACT OF HUMANS
• A. overexploitation
• B. habitat destruction
• C. introductions of exotic alien plants and
  animals (deliberately and accidentally)
• D. pollution

33
Basic Patterns in the Biogeography of the Pacific
Islands.

• Western relationships (affinity) of PIBD
  (relationships to Asia, Malesia and the Indo-West
  Pacific)
• Diversity gradient form west to east (attenuation
  of species and taxa)
• Gradual elimination of major groups of plants and
  animals from west to east in both the marine and
  terrestrial environment (i.e., increasing
  disharmony).

34
Basic Patterns in the Biogeography of the Pacific
Islands.

• Very high endemism on high isolated islands.
• Greater endemism among terrestrial and freshwater
  organisms than among marine organisms (gene flow
  and dispersal more restricted in the terrestrial
  and freshwater)
• Very low or no endemism on atolls and small
  low-lying islands  

35
Basic Patterns in the Biogeography of the Pacific
Islands.

• Increasing taxonomic (compositional) and
  structural complexity on larger, older islands.
• Changes in sea level (EUSTATIC) have affected the
  genetic background and the nature of the biotas
  and biodiversity of terrestrial, freshwater and
  marine biodiversity in the greater Indo-Pacific
  Biogeographical
•  

36
Basic Patterns in the Biogeography of the Pacific
Islands.

• Importance of successional change on islands due
  to natural and artificial disturbance.
• Primary and secondary successions
• r-adapted and K-adapted species
• The TAXON CYCLE ON islands and the gradual change
  for r-adapted species and evolution or change to
  specialized K-adapted endemics