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11.04 The Changing Climate and Insects

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Bugs 101: Insect-Human Interactions

Université de l'Alberta

4.8 (20 notes) | 5.5K étudiants inscrits

Of all the animals on earth, which are the strongest for their size? What about the fastest? Who were the first animals to evolve flight? Insects take all of these titles and more! As the most abundant animals on the planet, insects and other arthropods affect our lives in so many ways. From beneficial interactions like pollination and biological pest control, to the transmission of life threatening diseases; this course will teach you about the big ways that these little arthropods impact our lives. In Bugs 101: Insect-Human Interactions, you will be plunged into the diverse (and sometimes alien) world of arthropods to learn how they work, what they do, and how insects and humans interact every day. After completing this course, you will be able to: Describe the evolutionary relationships between insects and their arthropod relatives Inventory major groups of insects and their diversity Demonstrate evolutionary adaptations that make insects successful Discuss insect biology and human-insect interactions Evaluate positive and negative interactions between insects and humans Propose practical and symbolic roles insects play in human societies

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Compétences que vous apprendrez

Biology, Entomology, Science, Ecology

Avis

4.8 (20 notes)

5 stars
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VI

Aug 13, 2019

A study which is highly enjoyable and useful for professionals

CS

Aug 15, 2019

Overall a great course. Would, and have, recommend to others.

À partir de la leçon

Module 11: Insect Conservation

Many of us have thought at one time or another that the world may be better off without pest insects like mosquitoes. This module aims to change that view, as we discuss the importance of insect conservation and the variety of ways the changing world impacts insect populations.

11.04 The Changing Climate and Insects15:55

Enseigné par

Dr. Maya Evenden
Professor of Entomology

Transcription

In addition to landscape changes and habitat loss,

global climate change is

a major concern for insect conservation.

Human driven climate change has accelerated

the rate at which many species are now going extinct.

As of January 2018,

IUCN assessments revealed that

more than 250 species of insects are

vulnerable or endangered due to climate change.

This is because as small ectothermic animals,

insects have an undeniable relationship with temperature.

Recall the temperature influences multiple aspects of

insect biology from metabolic and developmental rates,

to the timing and level of insect activity.

It also affects insect survival.

Temperatures beyond the thresholds of

development for a given insect can slow growth,

and extreme temperatures can

kill members of an insect population.

It is logical then to expect

the temperature fluctuations will cause

changes to insect biology, behavior, and distributions.

In this video, we'll examine how

climate change affects insect biology,

population distributions, and biodiversity.

Let's begin at the biological level.

We know that warmer temperatures generally

promote faster rates of insect development,

thus allowing insects to reach sexual maturity

faster and complete more generations per year.

Interestingly enough, this can impact

the final body size of adult insects.

The well-established temperature size rule states that

ectothermic animals that develop under

warm conditions tend to grow faster,

mature earlier, and yet are smaller in maturation

compared to similar animals that

develop under cool conditions.

Although there are exceptions to

the temperature size rule,

this common pattern may be due to

physiological constraints on growth

experienced at higher temperatures.

A 2018 study showed that

the body size of native beetles in Canada has

declined by about 20 percent over

the last century in response to climate change.

Furthermore, the researchers found that

the body size of large beetle species

is declining disproportionately more

than that of small beetle species.

This has implications for

insect diversity in the face of climate change.

Body size influences several aspects of

an organism's life history

and ecology including lifespan,

home range, and reproductive success.

For example, small individuals may

produce fewer smaller eggs and

the resulting offspring maybe less capable of

exploiting their usual habitats or resources.

The effects of decreased body size

can potentially reverberate across

a food web through

the other organisms that insects interact with.

As we discussed earlier,

small insects maybe poor

quality prey for the predators that feed on them.

In addition to reduce prey quality,

a lower abundance of insect prey due to

reduced reproductive success can have

negative effects that carry throughout a food web.

Body size is not the only aspect of

insect biology that is affected by climate change.

Insect phenology is also

influenced by environmental changes.

We've established that

higher temperatures generally translate to

faster rates of insect development

and higher activity rates.

As such, a short winter or early spring due to

climate change can result in insects

becoming active earlier in the season than usual.

Similarly, a late onset

to winter could mean the insects have

a larger window of opportunity to

feed, grow, and reproduce.

Shifts in the timing of

insect life cycle events can

be detrimental to the insects,

if similar shifts in the timing of other events,

and ecosystem processes do not occur.

For example, an insect that emerges from

its over-wintering diapods earlier than normal,

may not have access to food or necessary habitats,

if the plants it relies on have yet to leaf out.

Alternatively, climate change may

induce a change in the phenology of the host plants,

which could result in a mismatch in the timing

of insect activity with resource availability.

The effects of climate change are

particularly significant to parasitoids.

They require very specific timing of life history events.

Many parasitoids have narrow habitat requirements,

are poor disperses,

and have intimate interactions with their insect hosts,

which can be disrupted if the host has

a different phenological responses to climate change.

If the parasitoid and hosts are mismatched in terms of

their spacial or temporal responses

to environmental changes,

regulation of a passed by

a parasitoid could be disrupted.

This was observed in the biological control of

the serial leaf beetle by a parasitoid wasp.

The beetle's development advanced

due to warming temperatures to

a greater degree than the development of

the wasp because they overwinter in different habitats.

The wasps overwinter in the shade,

while the beetles overwinter in the sun,

meaning that a warmer spring impacts

the beetles more than the wasps.

Parasitism by the wasp

declined in warmer temperatures because

the resulting larger beetle larvae

were less suitable hosts.

Warming temperatures can also have direct impacts

on the survival of insects that are habitats specialists.

Consider the ice bugs or

ice crawlers in the family Grylloblattidae.

These insects are adopted to live in

the cold environments of mountaintop

terrains with optimal temperatures

between one to four degrees Celsius.

Rising temperatures as a result of climate change will

cause mortality of these insects through overheating,

and will reduce the habitat available to them.

Declines in insect populations

due to rising global temperatures

have been documented across

taxa and ecosystems around the globe.

With one study indicating declines in two-thirds of

monitored populations with

an average decline of 45 percent.

Similar declines in insect populations

had been shown in a study

conducted across multiple insect

and vertebrate taxa in the tropics.

This trend was present despite

regular seasonal fluctuations in insect populations,

and has had a cascading effect through the food web.

In tropical climates, temperatures are

near optimal for many insect species,

and hence great species diversity

is supported in these regions.

Suitable environmental conditions allow

tropical insects to have high metabolic rates,

fast development, and rapid population growth.

As the globe warms,

temperatures in tropical regions will

rise above the optimal temperature,

and even the upper threshold temperature

for many of these species,

which could potentially lead to

reduced insect population growth rates in these areas.

In temperate regions, however,

average temperatures are lower

than optimal for most insects

and overall insect diversity

is lower than in the tropics.

In this case, as temperatures increase,

they may approach the optimal range

for metabolic activity,

development, and survival of many insect species.

Therefore, there is a high potential for

insect population growth and

range expansion in these regions.

As an insect's metabolic activity increases,

its rate of food consumption rises accordingly.

This means that we may begin to see a rise in

crop losses in temperate regions due to range expansion,

and increased insect activity.

A study conducted in 2018,

examined crop losses in rice,

maize, and wheat in relation to insect activity.

Models were used to predict how this may change as

insect populations vary with rising temperatures,

taking into account both insect and

crop responses to temperatures.

This study estimates that for

each degree of global surface warming,

we can expect 10-25 percent greater crop losses

for these grains across the world,

due to an increase in insect feeding activity,

and population growth.

These three grain crops account for 42 percent

of the direct calories consumed by people worldwide,

and are critically important to

feeding our global population.

We have discussed the many different ways climate change

can affect insect biology directly.

However, climate change can also have indirect effects

on insects through changes to the overall ecosystem.

Impacts from climate change can

occur at the ecosystem level

in the form of changes to plant assemblages and biology.

Changing temperatures, carbon dioxide levels,

and precipitation can alter

plant traits such as chemistry,

biomass, or seed production.

Some species of plants may also experience range changes,

including expansion in response

to climate-driven environmental changes.

While the effects of changes to plant biology on

the associated insect populations

have not yet been quantified,

it is likely that herbivorous insects will be impacted

directly through plant herbivore interactions.

This is especially true in the case of

monophagous and oligophagous species,

which are dependent on a specific host plant

or closely related plants for survival.

Insect herbivores in general have

a narrower diet than most vertebrate herbivores,

which might be one reason that insects are

more sensitive to ecosystem changes.

Impacts on herbivorous insects

will eventually reverberate

throughout the food web to

impact populations of predators,

parasitoids, and even pollinator species.

Many insect species respond

to climate-driven pressures on

their biology and access to

suitable resources by shifting their natural range.

Models predict that some insects will

respond to rising temperatures

with a shift in distribution,

either pole-wards or to higher elevations,

in order to remain within an optimal temperature range.

Estimates suggest that for

every one degree Celsius increase in temperature,

population distributions will shift

upward by an average of

170 meters in elevation or

150 kilometers pole-ward in latitude.

This type of range redistribution

has already been documented.

A study conducted in Massachusetts,

where temperatures have risen two

degrees Celsius in the last 100 years,

examined population distributions

of different butterfly species.

They found that butterflies adapted to warm climates,

have expanded their range northwards,

and increased in numbers,

while butterflies adapted to

cold have declined in the region.

To predict population responses within

a given region to weather patterns and climate change,

we use physiology-based models,

which take into account

the biology of the species in question.

These models predict that

many insects such as the European grapevine moth,

an important pest of grapes,

will respond to a warming climate with

increased populations in northern parts of their range.

At the same time,

the numbers in southern parts

of the range should diminish where

hot summer temperatures may

approach their thermal limits.

In the case of the European grapevine moth,

their response to rising temperatures is

expected to be similar to that of their grapevine hosts.

So their pest status will likely be maintained,

although, they will likely become

more important in the North.

The predictions obtained from

physiology-based models can be extremely useful to

estimate the regional impact of climate change

on both pests and beneficial species,

and to develop, evaluate,

and implement control strategies.

Populations of insects that have range shifts in

response to climate change

will face additional challenges.

If very few insects reach

the leading edge of a population expansion,

there may simply be too few individuals for

the insects to successfully locate each other and mate.

Additionally, some populations can

become isolated from each other,

such as those located on mountain tops.

For example, an upward shift in elevation may

result in the genetic isolation of those populations.

As we've discussed in the previous video,

such isolation can result in inbreeding depression

and ultimately lead to a decline in population health.

Not all insect species will be able

to make such distribution shifts,

however, due to geographical barriers

or limited dispersal capabilities.

Furthermore, novel habitats may

not always be suitable for colonization,

as they may have unsuitable micro climatic conditions,

low resource availability, or

high natural enemy abundance.

As a result, insect species that

are unable to shift their range in

response to climate change may be at

substantial risk of extinction.

Although insects are sensitive to climate change,

there's remarkable variation in

tolerance levels within populations,

and short generation times may allow

insect populations to adapt

quickly to a changing climate.

If rapid adaptive evolution occurs,

local insects maybe able to persist in

the region despite climatic changes.

The winter moth is an interesting European moth that may

provide a case study for

insect adaptation to climate change.

These aptly-named moths are one of the few insects

that remain active in late fall or early winter,

and produce eggs that

overwinter before hatching the following spring.

Climate change has led to asynchrony between

their egg hatch and the leaf flush of their host plant,

European oak, with eggs hatching

up to two weeks before leaf flush.

This asynchrony could lead to starvation of

the caterpillars and a severe population decline.

However, there has been evidence of

two adaptations to counter this asynchrony.

The first is a host switch,

as the caterpillars are not specialists on European oak.

Other trees in the moth's habitat leaf

out earlier than the European oak.

The host switching allows the caterpillars to use

a different food source if they

hatch before the oak leaves flush.

The second adaptation is a delay in egg hatch,

in which the timing of egg hatch has been realigned

to leaf flush of European oak to restore synchrony.

Where other host trees are not available,

regaining synchrony is necessary

to prevent starvation of the caterpillars.

The effects of global climate change

on insect diversity are

difficult to quantify as

there are many variables involved.

Other than temperature changes,

there are also changes in weather patterns and intensity.

The effects of climate change on

species also differ among

individuals, populations, and communities.

As the world changes,

insects can either adapt quickly to

the habitat change or

disperse to find alternative habitats.

If insects cannot move or adapt,

they may go locally extinct

in response to climate change.

Each of these responses will

have ramifications on ecosystems.

The presence of new species can

impact many aspects of an ecosystem,

as we'll expand on in the next lesson,

while emigration or loss of insects from an area

could result in the loss

of important ecosystem functions.

Landscape and climate change are not

the only human-associated factors

leading to a decline in insect diversity.

In the next video, we'll discuss

two other factors that contribute to

the loss of insect biodiversity,

the spread of invasive species, and over-harvesting.

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