In addition to landscape changes and habitat loss, global climate change is a major concern for insight 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 that 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 that 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 may be 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 may be 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 lifecycle 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 overwintering diapause 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 dispersers, and have intimate interactions with their insect hosts which can be disrupted if the host has a different phenological response to climate change. If the parasitoid and host are mismatched in terms of their spacial or temporal responses to environmental changes, regulation of a pest by a parasitoid could be disrupted. This was observed in the biological control of the serial leaf beetle by a parasitoid wasps. 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 habitat specialists. Consider the ice bugs or ice crawlers in the family guilability. 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 rising 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 to 25 percent greater crop losses for these grains across the world due to an increase in insect feeding activity and population growth. These three green 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 them 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 monofagus and oligofagus 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 reverberates 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 polewards 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 poleward 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 adopted 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 the 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 there 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 may be 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 mods are one of the few insects there 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 caterpillar's 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 moths habitat leaf out earlier than the European Oak and 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 asynchrony. 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.
