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)
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
(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)
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
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: Pierce’s disease, Dutch Elm disease
Why give a lecture on insects in BLD18?
From Gullan & Cranston (Insects: an outline of
entomology)
(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
Why give a lecture on insects in BLD18?
From Gullan & Cranston (Insects: an outline of
entomology)
II. What are insects?
Insects are in the phylum Arthropoda
OK, 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!
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
Hemimetabolous Holometabolous
II. What are insects?
From Gullan & Cranston (Insects: an outline of
entomology)
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
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?
Female lays singleegg in host
Larva developsIn head capsule
New adult emergesfrom head capsule
Female attractedto healthy host
Larva pupariatesIn head capsule
Larva eventuallydecapitates host
Life cycle of ant-decapitating flies
Sanford Porter Photo
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
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
III. Why are insects so diverse?
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 >1,000,000 described insect species
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 can’t estimate to the nearest order of magnitude how many insects exist
estimates range from 3-30 X 106
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
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
IV. How many species of insects?
Erwin found > 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
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
Erwin’s provocative result greatly exceeded previous estimates
IV. How many species of insects?
Erwin’s 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.
(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
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 (top–order carnivores), insects may be
more likely to persist in small fragments
V. Insect conservation: causes of imperilment
10
20
30
40
50
60
urban 0-25 26-50 51-100 >100
Distance (m) to nearest urban edge
urban matrixmesic fragmentsxeric fragments
Argentine ants / pitfall trap
V. Insect conservation: causes of imperilment
0
0.4
0.8
1.2
1.6
0 0.5 1 1.5 2 2.5 3
log area (ha)
xeric fragmentsmesic fragmentsplots withinunfragmented areas
- 0.5
Log (number of native ant species)V. Insect conservation: causes of imperilment
(3) Habitat destruction
currently the leading cause of insect endangerment globally
lion’s 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
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 391:72-76.
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
V. Insect conservation: causes of imperilment
birds
beetles(flying)
canopy ants
termites
butterflies
beetles(canopy)
leaf-litterants
nematodes
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
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
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
(1) 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?
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 414:65-67.
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
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
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
can’t colonize isolated patches of habitat
- decline in abundance as a result
V. Insect conservation: causes of imperilment
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)
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
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
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
VI. Insects & the endangered species act (esa)
Jobs versus flies?
NY Times (12/1/02)
VI. Insects & the endangered species act (esa)