I' Why give a lecture on insects in BLD18

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• I. Why give a lecture on insects in BLD18?
• II. What are insects?
• III. Why are insects so diverse?
• IV. How many species of insects?
• V. Insect conservation causes of imperilment
• VI. Insects the endangered species act (esa)

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Why give a lecture on insects in BLD18?

• (1) Insects are extremely important in natural
  systems
• The little things that run the world (E.O.
  Wilson)
• central role of insects in most terrestrial
  ecosystems
• Insects perform numerous ecosystem services
• scavengers, predators, detritivores herbivores
• prey for many vertebrates other invertebrates
• pollinators, seed dispersal, plant protection

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Why give a lecture on insects in BLD18?

• (2) Insects are beneficial to humans
• biological control (predators parasites)
• pollination (honeybees)
• - 1 out of 3 bites of food people eat
• silk production (silk moth - Bombyx mori)
• food (non-western cuisines)
• aesthetics (bees butterflies)

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Why give a lecture on insects in BLD18?

• (3) Insects are harmful to humans agricultural
  pests
• herbivores that use the same resources as humans
• pest is an anthropocentric designation
• crop losses to insects have remained constant or
  have increased with advent of pesticides

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Why give a lecture on insects in BLD18?

• (4) Insects are harmful to humans vectors of
  diseases
• Vector insect that carries a disease from one
  host to another
• human diseases vectored by insects malaria,
  sleeping sickness, plague, encephalitis, dengue,
  Chagas disease,
• west nile virus
• plant diseases vectored by insects Pierces
  disease, Dutch Elm disease

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From Gullan Cranston (Insects an outline of
entomology)
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Why give a lecture on insects in BLD18?

• (5) Insects are fantastically diverse
• perhaps 64 or more of estimated number of all
  species
• over 106 described species of insects
• 56 of all described species are insects
• Insect conservation now seen as imperative
  to preserving biodiversity
• a species to which a binomial Latin name
  (e.g., Drosophila melanogaster) has been assigned
  by a taxonomist in a scientific publication

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From Gullan Cranston (Insects an outline of
entomology)
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II. What are insects?Insects are in the phylum
ArthropodaOK, but what are arthropods?(1)
Trilobites wholly marine and extinct 4000
described species(2) Crustaceans mostly
marine freshwater 30,000 described spp.(3)
Chelicerates a few marine, many terrestrial
65,000 described spp.(4) Pycnogonids all
marine 4,000 described spp.(5) Myriapods
terrestrial centipedes millipedes 13000
described spp.(6) Hexapods mostly
terrestrial, a few freshwater c. 1,000,000
described species!
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II. What are insects?
Shared, derived features of the Class
Insecta (1) compound eyes (2) gas exchange
is predominantly tracheal (4) three body
segments head, thorax, abdomen (5) most have
wings relative to other hexapods
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II. What are insects?
Hemimetabolous Holometabolous
From Gullan Cranston (Insects an outline of
entomology)
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Coleoptera (beetles) c. 350,000 described
species Diptera (flies) c. 125,000 described
species Lepidoptera (butterflies moths) c.
160,000 described species Hymenoptera (ants,
bees wasps) c. 100,000 described species
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III. Why are insects so diverse?

• (1) Small size (0.2 300 mm)
• insects divide the environment finely
• (2) Old age (most extant groups 250-300 million
  years old)
• insects have had time to fill explore
  environment
• (3) Associations with other organisms
• especially with plants other insects
• herbivores, parasites, parasitoids,
  hyper-parasitoids
• Does diversity beget diversity?

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III. Why are insects so diverse?
Life cycle of ant-decapitating flies
Sanford Porter Photo
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III. Why are insects so diverse?

• (4) Short generation time
• insects capable of rapid population growth
• (5) Winged flight
• only other extant flying animals are birds and
  bats
• avoid predators and high temperatures
• seek out mates, colonize new areas, migrate
  disperse

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III. Why are insects so diverse?

• (6) Metamorphosis
• life history divided into two separate stages
• (1) larval feeding growth
• (2) adult reproduction dispersal
• (7) Diapause
• period of arrested development
• permits survival in seasonally inhospitable
  environments

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IV. How many species of insects?

• Biologists have long realized the great diversity
  of insects
• 1758 Systema Naturae Carl Linnaeus listed 2000
  insect species
• 1883 Ray (British entomologist) 20,000 species
• 2000 gt1,000,000 described insect species

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IV. How many species of insects?

• Biologists have long realized the great diversity
  of insects
• described insects an unknown fraction of total
• no central, organized database for the life on
  earth
• unclear how many described species exist
• - synonyms, narrow regional surveys
• biologists still cant estimate to the nearest
  order of magnitude how many insects exist
• estimates range from 3-30 X 106

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IV. How many species of insects?

• How is diversity estimated in the absence of
  described taxa?
• (1) estimate tropical diversity by extrapolating
  from patterns
• found in well-studied faunas of temperate
  regions
• on average, there are 2 tropical mammal species
  for every temperate mammal species
• 2X as many topical insects than temperate ones?
• such extrapolations assume that tropical
  temperate species
• ratios hold constant across phylogenetic
  groups
• little evidence for this groups often have
  idiosyncratic latitudinal
• diversity relationships

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IV. How many species of insects?

• How is diversity estimated in the absence of
  described taxa?
• (2) estimate tropical diversity by extrapolating
  from patterns
• found in well-studied faunas of tropical
  regions
• In the 1980s, British entomologist Terry Irwin
  drew attention to the potential for tropical
  insect diversity to far outstrip previous
  estimates
• Erwin used insecticidal fog
• to knock down beetles from 19
• Luehea seemannii trees in the
• Amazonian rainforest of Peru

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IV. How many species of insects?

• Erwin found gt 1100 species of beetles -
  Remarkable!
• Partitioned beetles into feeding categories
• (e.g., carnivore, scavenger, fungivore, and
  herbivore)
• Guessed that 5, 10, 5 and 20 of the species
  in each feeding category were restricted to
  Luehea seemannii
• Estimated that c. 160 species of beetles might
  be specialized on a typical tropical tree species

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IV. How many species of insects?

• Erwin further speculated that
• 400 species of unique canopy arthropod species
  per tree species
• beetles are 40 of known arthropod species
• 600 species of arthropods per tree
• 2X as many arthropods occur in canopy compared
  to the number found on the forest floor
• 50,000 tropical tree species X 600 arthropods
  per tree 30 X 106
• Erwins provocative result greatly exceeded
  previous estimates

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IV. How many species of insects?

• Erwins estimate high but illustrates
• The potential for insect diversity to far exceed
  that of other animals
• Most diversity will be found in the big four
  insect orders Coleoptera, Lepidoptera
  Hymenoptera, and Diptera
• How little we know about diversity
• Most taxonomists (those who name classify
  organisms) work in the species poor north,
  whereas most insect species are tropical
• Per taxon, far more scientists work on
  vertebrates than invertebrates.
• Taxonomists are not being trained to replace
  those who retire.

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V. Insect conservation causes of imperilment

• (1) Introduced species
• some intentionally introduced (e.g., biological
  control agents)
• many others introduced by accident as a result
  of commerce
• rate of introduction continues to increase with
  globalization
• direct effects
• e.g., native ants displaced by Argentine ants
• indirect effects
• e.g., host plants of an herbivore displaced by
  invasive plants
• e.g., bio-control agents that share enemies
  with native species

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V. Insect conservation causes of imperilment

• (2) Habitat fragmentation
• natural habitats surrounding areas occupied by
  people are often
• fragmented
• fragmentation compromises the biota
• altered hydrology
• edge effects by invasive species
• reduction in size of populations
• increased isolation of populations
• unlike like some vertebrates (toporder
  carnivores), insects may be
• more likely to persist in small fragments

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V. Insect conservation causes of imperilment
Argentine ants / pitfall trap
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V. Insect conservation causes of imperilment
Log (number of native ant species)
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V. Insect conservation causes of imperilment

• (3) Habitat destruction
• currently the leading cause of insect
  endangerment globally
• lions share of insect biodiversity resides in
  tropical forests
• preservation of these habitats will go a long
  ways to preserving not
• only insect biodiversity but biodiversity
  generally
• few comprehensive studies have been attempted to
  determine how
• conversion of tropical forests will affect
  insect diversity

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V. Insect conservation causes of imperilment

• (3) Habitat destruction
• Lawton et al. 1997. Biodiversity inventories,
  indicator taxa and effects of habitat
  modification in tropical forest. Nature
  39172-76.
• sampled 8 groups birds, butterflies, ants
  (litter canopy), beetles (flying
• canopy), termites nematodes across a
  disturbance gradient in
• Cameroon rain forest
• disturbance gradient primary forest, secondary
  forest, secondary forest
• commercial plantation, fallow fields
• plantation tree was a common native species

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V. Insect conservation causes of imperilment
birds
butterflies
beetles (flying)
beetles (canopy)
canopy ants
leaf-litter ants
termites
nematodes
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V. Insect conservation causes of imperilment

• (3) Habitat destruction
• Main points of Lawton et al. study
• all taxa (except nematodes) decreased sharply in
  species richness across
• disturbance gradient
• species turnover varied across taxonomic groups
• no single group adequately predicted declines in
  any other group

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V. Insect conservation causes of imperilment

• (4) Climate change
• insects are profoundly affected by subtle changes
  in climate
• in the face of a changing climate insects may
• tolerate
• adapt
• shift their ranges
• suffer extinction
• potential effects of climate change currently an
  active area of research,
• but one with many uncertainties

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V. Insect conservation causes of imperilment

• (4) Climate change
• climate change is a natural phenomenon, but two
  important factors
• distinguish anthropogenic climate change from
  past events
• it is occurring much more quickly
• (2) in many areas natural habitats will exist
  primarily in a
• fragmented state lack of habitat connectivity
  may
• hinder movement among fragments
• Will climate change fragmentation interact to
  increase extinctions?

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V. Insect conservation causes of imperilment

• (4) Climate change
• Warren et al. 2001. Rapid response of British
  butterflies to opposing forces of climate and
  habitat change. Nature 41465-67.
• amateur lepidopterists compiled fine-scale
  distributional data for last
• several decades, during which time UK climate
  has experienced warming
• 46 non-migratory butterflies all near N edge of
  their ranges in UK
• many confined to warm micro-sites might be
  expected to undergo range
• expansions under global warming

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V. Insect conservation causes of imperilment

• (4) Climate change
• instead most species declined over the past 30
  years
• 89 sedentary habitat specialists (open symbols)
  shrank in distribution
• 50 of mobile, habitat generalists (closed
  symbols) increased in distribution

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V. Insect conservation causes of imperilment

• (4) Climate change
• Changes in distribution correlated with changes
  in abundance
• consistent with habitat loss interacting with
  climate change
• - sedentary species differentially susceptible
  because they
• cant colonize isolated patches of habitat
• - decline in abundance as a result

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VI.Insects the endangered species act (esa)

• In US, insects obtain protection under the
  endangered species act (1973)
• globally unique piece of legislation but not
  without its problem
• (1) species get listed too late threatened
  endangered
• (2) political circumstances can affect particular
  listings
• (3) historical focus has been on species
  preservation (as
• opposed to habitat preservation)

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VI. Insects the endangered species act (esa)

• listed vertebrates (e.g., California Condor) far
  outnumber listed insects
• most listed insects are butterflies but this
  probably reflects
• degree of knowledge about these conspicuous
  insects
• aesthetic considerations
• non-butterflies listed as endangered frequently
  elicit controversy

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VI. Insects the endangered species act (esa)

• Delhi sands flower-loving fly
• sedentary, habitat specialist
• formerly occupied 40 mile2 area
• of dunes in SW SBD NW RIV Cos.
• 98 of this habitat has been
• converted either to agriculture or
• urban developments
• remaining 2 (vic. Fontana
• Colton) heavily fragmented

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VI. Insects the endangered species act (esa)

• Delhi sands flower-loving fly
• fly listed in 1993 as endangered
• listing prevented some planned developments from
  being built
• outcry of local politicians some media sources
• upside of listing last fragments of a rare
  ecosystem preserved

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VI. Insects the endangered species act (esa)

• Jobs versus flies?

NY Times (12/1/02)