Introduction.
Background, Rationale, Goals & Expectations
Topic Importance.
The greatest challenge for modern ecology is understanding the effects of climate change within Earth’s ecosystems (Garcia et al., 2014). It is especially important to gain this understanding in relation to insect groups because of their large diversity and vital role in the functioning of our freshwater and terrestrial ecosystems (Halsch et al., 2021). All insects respond directly and indirectly to changes in climate variables (Stenage and Ayres, 2010) however we are still building knowledge on the long-term and population-level responses of many insect groups (Kocsis and Hufnagel, 2011; Halsch et al., 2021). Studies looking at climate variation are especially limited (Barton et al., 2019; Halsch et al., 2021).
Figure 1. Relative biodiversity of extant organisms. (Dow et al., 2018)
Climate Variables & Insects.
Just like temperature and precipitation vary spatially, insect sensitivities and responses to climate change also vary both spatially and between groupings (Stange and Ayres, 2010). This makes population and community-level responses hard to predict. The main mechanism that insects respond to is the physiological limits that climate variables directly set (Stange and Ayres, 2010). These prescribed limits can largely and rapidly affect insect abundance throughout a spatial area (Stange and Ayres, 2010). Typically, temperature has a positive relationship with insect abundance whereas precipitation typically has a negative relationship with insect abundance (Halsch et al., 2021).
Current Knowledge.
Warmer temperatures have been observed to accelerate the metabolic rate and fecundity of insects in the summer, resulting in higher abundances (Sharpe and DeMichele, 1977; Gillooly et al., 2002). Warmer springs have also allowed insects to feed and mature earlier in the season, also resulting in higher abundances (Ayres, 1993; Stange, 2009). Finally, warmer winters directly reduce winter mortality due to harsh low temperatures, resulting in higher abundance in the following year (Ayres and Lombardero, 2000).
Figure 2. Impacts of increasing temperature on insects. (Skendžic et al., 2021)
Figure 3. Impacts of precipitation on insects. (Skendžic et al., 2021)
Considering precipitation, winters with less snow have been observed to increase winter mortality due to the lack of a protective buffer layer under the snow(Lombardero et al., 2000). In addition, droughts caused by less precipitation have been observed to affect insect physiology and food sources, resulting in smaller abundances (Halsch et al., 2021). These are just a small sample of the cause-effect relationships between temperature and insect abundance, and the understanding of these relationships is continually being explored (Halsch et al., 2021). To contribute to this exploration, the need for long-term monitoring is apparent due to its uniquely powerful quality for understanding ecological effects using climate variables (Halsch et al., 2021).
Project's Contribution.
The Zoological Museum at the University of Copenhagen in Denmark has consistently collected insect abundance data for two insect Orders between 1992 and 2009. The availability of 18 years' worth of data is an excellent opportunity to contribute to the growing knowledge of long-term climate effects. Previous work has been done using this dataset (Thomsen et al., 2015) however, they focused on abundance at the species level and temperature effects of species and resource specialists. This project is unique as it will look at abundances at a higher taxonomic level, will incorporate the effects of precipitation, and will look at climate variation.
This project wanted to answer the question: What are the effects of precipitation and temperature on insect abundance (Orders Lepidoptera and Coleoptera) in Copenhagen, Denmark between 1992-2009?
Three objectives were made to answer the research question;
1.
Determine the monthly differences in insect counts at the Family level for both insect Orders to understand the overall community dynamics of the common insects found within the city.
2.
Investigate the relationships between temperature and insect abundance to make potential inferences about the effects of increasing temperatures due to climate change.
3.
Investigate the relationships between precipitation and insect abundance to make potential inferences about the effects of changing hydrological events due to climate change.
Expected Results.
Within the Order Coleoptera, it was expected that years with higher average monthly temperatures would have higher Family abundances than years with lower average monthly temperatures. In addition, years with lower average monthly precipitations were expected to have lower Family abundances than years with higher average monthly precipitations.
The same expectations were made for the Order Lepidoptera, however, it was expected that Family abundances would differ more to changes in temperature and precipitation because insects within this Order are particularly sensitive to climate variables (Kocsis and Hufnagel, 2011), with many even considering them as indicator species (Ronkay, 2004).
Phyllonorycter platani, a species counted 146 times at the Zoological Museum between 1992-2009 (image link)
Polydrusus cervinus, a species counted just 1 time at the Zoological Museum between 1992-2009 (image link)
It was not certain whether insect abundance would be dependent upon the climate variables in this project. In fact, many long-term insect studies have not found climate-dependent trends within their studied insect populations (Halsch et al., 2021). However, these results are still significant contributions to our knowledge base as they can indicate other processes going on within the spatial area or even buffering of climate dependencies by high-quality habitats that could be further explored (Halsch et al., 2021).