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Summary
Ecological Consequences of Artificial Night Lighting
Text based on::
Catherine Rich, Travis Longcore, Editors
Island Press, 2006
ISBN 1-55963-129-5
Images:
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Effects of Artificial Light:
- Orientation and Attraction/Repulsion
- Reproduction
- Communication
- Competition
- Predation
- Ecosystem disruption
Complex Ecosystem
Effects of Artificial Light
An ecological system is a complex web of
relationships between animals and their
surroundings. Living things respond in a variety of
ways to impacts on the environment. Some
examples of the effect of light at night are well
known - moths gathering around a street lamp, or
the harvesting of fish with spotlights - but the long
term impacts and changes to the ecosystem are not
well understood. These changes can have a
dramatic effect on humans - as for example the
negative impact of light at night on the salmon
fishery.
Terrestrial Mammals
Terrestrial Mammals
Possible effects:
- disruption of foraging behaviour
- increased risk of predation
- disruption of biological clocks, affecting mating success
and group-mediated anti-predator vigilance
- increased road deaths due to blinding and disorientation
- disruption of dispersal movements and corridors
Increased highway lighting is not effective in reducing deer-car
collisions.
Terrestrial Mammals
Many mammals (small carnivores, rodents) are nocturnal.
These are affected by light at night.
Night-adapted animals have a rod-based retina, which
provides the necessary sensitivity for night vision but blinds the
animal in bright light. Light (moonlight) increases the risk of
predation, so small mammals stay hidden.
A light level of 0.2 lux was sufficient to suppress melatonin
production in rats and enhance tumor production.
Bats
Bats
Insects are attracted to lights, bats then gather in the
lights to feed on these insects.
Moths evade bats by detecting their ultrasound, but
moths do not use this warning in bright light, so they
are an easy target.
Bats
In several mountain valleys in switzerland, the lesser
horseshoe bat became locally extinct after
streetlights were installed. They were replaced by
pipistrelle bats, who feed at streetlights
Migrating Birds
Migrating Birds
Migrating Birds
Migrating birds tend to move toward light and
are reluctant to leave the
lighted area.
- delays migration
- mortality due to exhaustion and
collision with structures.
Floodlit structures attract and kill birds,
particularly in misty weather.
Sea Turtles
Sea Turtles
Hatching turtles are disoriented by artificial light, causing
them to go inland instead of to the sea. Artificial light also
aids predation of the hatchlings.
A number of measures have been taken with some success.
These include shielding of luminaires, reducing light output,
installing motion detectors and light curfews, and LED
lighting embedded in roadways. All coastal buildings must
now have a lighting plan. However, problems continue with
population growth and lighting further inland that creates sky
glow. Local lighting controls are not a complete solution.
Reptiles
Gecko
Reptiles
Rattlesnakes and water snakes hunt in the
dark of the new moon. These species have
declined in areas of heavy light pollution.
Gecko mating is curtailed in artificial light.
Frogs and Toads
Frogs and Toads
Frogs and toads have extremely sensitive night vision,
and can see in light levels of 10^-6 to 10^-5 lux.
(Moonlight is typically about 1 lux). They are nocturnal,
so light at night affects them and their predator-prey
relationship. Some species are attracted to light, which
acts as an 'evolutionary trap'.
Mating behaviour (chorusing) and fertility (in toads) are
inhibited under artificial light. After exposure to bright
light (along a highway, for example) frog night vision
can take hours to restore to night vision sensitivity.
Salamanders
Newt
Salamanders
Salamanders are are aquatic animals. Newts rely
on the day-night transition to initiate foraging, and
rely on the characteristics of natural light for
navigation.
Artificial light interferes with both these activities,
and may be one factor in their population decline.
Fishes
Sea Trout
Fishes
Some fish species are attracted to light, and
fishing vessels use high-intensity lamps to attract
their prey. Mercury-vapour lamps have been
used to attract fish into special channels around
dams and power stations.
Other fish species avoid light. In Scotland, lights
from a tennis court eliminated sea trout from a
nearby river.
Fishes
Juvenile rainbow trout are inhibited from foraging by moonlight or
artificial light. Darkness is essential for fish to avoid predation.
Harbour seals have learned to use artificial light to outmigrating
smolts.
Salmon fry are inhibited from
migration by light levels in excess
of 1 lux.
Several species are inhibited
from spawning (laying eggs) by
light at night
Insects and Streetlamps
Insects are critically important as pollinators and members
of food webs in an ecosystem.
Lamp Effects on beetles, moths, flies, caddisflies:
Fixation or Capture Insect cannot escape near zone of the
light.
Crash Barrier Flight path is interrupted so insects cannot
migrate
Vacuum Cleaner Insects are removed from the area local to
the lamp.
Insects and Streetlamps
Insects and Streetlamps
Radius of attraction: 400 to 600 metres under full
darkness, 40 to 60 metres under full moon.
In dark zones, the attraction has been 2000 to 11000
insects per night. In a rural village with lighting, 400 to
1600 insects per night per lamp. Approximately 1/3 of the
insects are killed or incapacitated.
In order, worst to best, are high-pressure mercury, highpressure sodium and low-pressure sodium lamps. Insect
attraction can be reduced with a UV filter.
Insects and Streetlamps
Mayflies
Moths
Moths
Areas around artificial lights function as bat, bird,
gecko and spider feeding stations. Some bats live only
a few days, so any disruption of their behaviour has an
effect on the population. Light interferes with dispersal,
which inhibits resistance to habitat fragmentation.
Light greater than 0.05 lux inhibits mating in one
species of moth.
Moths
Lamp with ultraviolet component (mercury vapour,
LED) is a strong attractant. Low pressure sodium
vapour rarely attracts moths. Individual lamps attract
more strongly than an aggregate of lamps.
One lamp trap collected 50,000 moths in a single
evening. A typical catch rate is 4 to 10,000 insects per
year.
Artificial light can inhibit moth parasites.
Fireflies
Artificial light swamps the
luminescent mating
communications of fireflies.
Continuous light (due to
skyglow) may affect the
timing of development from
pupa to fly. Artificial light
inhibits the resettlement of
fragmented habitat (light
barrier effect).
Freshwater Habitats
Plankton
Daphnia
Freshwater Habitats
Zooplankton are at the bottom of the food chain, so their
health impacts the marine ecosystem. Nocturnal marine
organisms respond to light of full moon (0.05 to 0.1 lux).
Zooplankton rise to the surface at night. Artificial
light suppresses zooplankton migration.
Cued by low light, stream insects (eg, caddisfly larvae)
migrate downstreamat night while foraging.
Plant Responses to Artificial Lighting
Plant Responses to Artificial Lighting
There are four photoreceptor families. These have
different spectrum responses in order to control the
timing of growth (eg, germination) under various
conditions (direct sun, open sky, shade).
Photoperiodism: some plants are sensitive to the length
of the day.
Daylight extension inhibits the flowering of some plants
and encourages it in others. A brief exposure to light
will inhibit the cockleburr from flowering. Some trees
exposed to lighting exhibited late season growth
followed by severe winter dieback. Security lighting
around prisons prevents soybeans from growing, within
30 metres of the source.
Minimizing the Impact of Artificial Light
on an Ecosystem
Turn lights off when they are not needed
Reduces the impact on nocturnal insects, animals and on plants.
Limit the extent of lighting
Minimizes environmental impact and sky glow
Use new lighting methods:
Example: buried LED lamps in coastal highway
Consider the impact of spectrum
Example: some insects are particularly sensitive to ultraviolet
LPA Guideline
How do we incorporate ecological concerns in the LPA
Guideline?
We assume ecology has relevance in the urban
environment.
Option 1: Appendix of significant length with images
Option 2: Brief mention with a few examples.
Tone and Orientation: Positive, eg, light pollution
abatement measures will also aid the ecology of birds,
insects and marine animals.
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