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I' Why give a lecture on insects in BLD18

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Title: I' Why give a lecture on insects in BLD18


1
  • 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)

2
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

3
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)

4
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

5
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

6
From Gullan Cranston (Insects an outline of
entomology)
7
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

8
From Gullan Cranston (Insects an outline of
entomology)
9
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!
10
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
11
II. What are insects?
Hemimetabolous Holometabolous
From Gullan Cranston (Insects an outline of
entomology)
12
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
13
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?

14
III. Why are insects so diverse?
Life cycle of ant-decapitating flies
Sanford Porter Photo
15
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

16
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

17
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

18
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

19
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

20
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

21
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

22
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

23
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.

24
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

25
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

26
V. Insect conservation causes of imperilment
Argentine ants / pitfall trap
27
V. Insect conservation causes of imperilment
Log (number of native ant species)
28
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

29
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

30
V. Insect conservation causes of imperilment
birds
butterflies
beetles (flying)
beetles (canopy)
canopy ants
leaf-litter ants
termites
nematodes
31
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

32
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

33
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?

34
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

35
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

36
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

37
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)

38
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

39
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

40
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

41
VI. Insects the endangered species act (esa)
  • Jobs versus flies?

NY Times (12/1/02)
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