They are the most diversified animal group on the planet. They are key ecosystem engineers - even with their small size. They include insects, snails, earthworms, millipedes and even spiders, and have been called “the little things that run the world" (Wilson, 1987). They are the invertebrates!
These tiny creatures have a very long evolutionary history and make up 95 to 97 per cent of known animals. So as these “little things that run the world”, what exactly do they do to help Earth and humans alike?
Kotze (2022) states that key truths can be found in the forests. Some invertebrates are intentional engineers, meaning they specifically make networks of nests, such as ants and termites. Others are accidental engineers, making temporary tunnels and through this excreting additional nutrients as they go, like termites.
Whether intentional or accidental in their actions, they all have a huge part to play in the Earth’s ecosystem and are very important. As the world becomes increasingly urbanised, it is important to protect these important creatures and create habitats and safe spaces for them, in green areas such as parks, verges, home gardens, and also areas called urban forests.
In Kotze’s 2022 study, urban forests are defined as “self-regenerating communities with a tree canopy that exist as remnant pacts of formerly contiguous habitat now surrounded by urban areas”, and alongside Alvey’s 2006 study, includes trees and vegetation along streets, in gardens and in parks.
We have lots of urban forests around us here in Australia! Kotze’s (2022) study researched the link between urban forests and invertebrates, to find that the importance of invertebrates for our ecosystem is greater than we might even initially think.
In this time of the Anthropocene, the current geological time period we said to be in, characterised by habitat loss and climate change (Crutzen, 2006), and a time when human activity has become the dominant influence on our climate and ecosystems, urban forests are more than ever becoming important refuges for our invertebrate friends.
There are several important functional roles that invertebrates take in urban forests.
Roles of invertebrates
• Pollination - integral for continuing generations of plant species to grow and thrive. Within urban forests, pollinators can find plenty of habitat resources. Kotze’s 2022 study also found that it is very important to have a range of different plant species. Large trees that feature in canopies, smaller trees, shrubs, ground covers and weeds are all important to ensure diversity within our ecosystems and all invertebrates have different foraging and nesting needs.
• Seed Dispersal - as many of these seeds and microbes are sessile (permanently attached to a surface), invertebrates are so important to ensure their dispersal and some plants have even co-evolved with bugs to ensure dispersal is achieved by a specific species. For example, the seeds of Acacia have evolved to enable dispersal by ants (Ward and Branstetter, 2014).
• Predation - top-down regulated interactions are important for our ecosystem to thrive, and without a sufficient invertebrate population, urban pest populations can grow. High biodiversity levels can help to regulate populations and pests, limiting the use of pesticides.
• Soil health - having a healthy population of invertebrates also helps to maintain sufficient organic matter decomposition, assisting our soils will remain healthy. Earthworms, woodlice and millipedes are all invertebrates that can help return nutrients back to the soil, and have already found to have made a difference in enhancing the process of decomposition in urban forests in Melbourne (Ossola et al., 2016).
Invertebrates can of course cause some disservices to humans, through property damage by termites or transmitting diseases by mosquitoes and ticks. The key factors are to be aware of the overall picture and not to demonise these important creatures.
Filter Factors
Kotze’s 2022 study also reviewed how city and town environments can act as filters for species survival (Brousseau et al., 2018).
Invertebrates can be quite sensitive to changes in their habitats, so even taking away leaf litter can cause major disruptions in populations. Soil trampling by humans can also affect them greatly as the soil gets compacted and reduces their ability to burrow or dwell in the soil. Temperature, wind flow and structure of the forest can be another major factor alongside pollution; chemical substances, microplastics and noise stress may cause population decline, but according to
Kotze’s 2022 study, the filter with a particularly obvious effect is light pollution.
Artificial lights can drive away species with severe sensitivity to light, like bats and micro-bats, and if a whole species is driven away from the environment, this can cause problems with the topdown predation interactions.
Species that are hunted by those driven away could increase, but then would become too strong a predator for the species further down the cycle. This instability can cause real problems when trying to increase and maintain our biodiversity levels for all those ecosystem services.
Helping Invertebrates
What can we do to help invertebrates, keep biodiversity levels up and promote the growth of urban forests?
By reducing our chemical pollutants, by promoting growth of different plants in our green spaces and gardens, and even by remembering to turn the outside light off at night, our actions can help our invertebrate friends.
Getting involved by volunteering with your local council’s urban forest, or even in our back gardens can help.
Maintaining leaf litter, having areas of non-altered soils, protecting water bodies, promoting native and endemic plant species and vegetation biodiversity can all help.
Just as invertebrates are “the little things that run the world”, even our little actions can help too.
Article written by Skye Brook
References:
Primary Reference:
1. Kotze, D.J., Lowe, E.C., MacIvor, J.S. et al. Urban forest invertebrates: how they shape and respond to the urban environment. Urban Ecosyst 25, 1589–1609 (2022). https://doi.org/10.1007/s11252-022-01240-9.
Secondary References:
2. Wilson, E. O. (1987). The Little Things That Run the World (The Importance and Conservation of Invertebrates). Conservation Biology, 1(4), 344–346. http://www.jstor.org/stable/2386020.
3. Crutzen, P.J. (2006). The “Anthropocene”. In: Ehlers, E., Krafft, T. (eds) Earth System Science in the Anthropocene. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-26590-2_3.
4. Alvey AA (2006) Promoting and preserving biodiversity in the urban forest. Urban For Urban Green 5:195–201. https://doi.org/10.1016/j.ufug.2006.09.003.
5. Philip S. Ward, Michael G. Branstetter; The acacia ants revisited: convergent evolution and biogeographic context in an iconic ant/plant mutualism. Proc Biol Sci 1 March 2017; 284 (1850):20162569. https://doi.org/10.1098/rspb.2016.2569.
6. Ossola, A., Hahs, A.K., Nash, M.A. et al. (2016) Habitat Complexity Enhances Comminution and Decomposition Processes in Urban Ecosystems. Ecosystems 19, 927–941. https://doi.org/10.1007/s10021-016-9976-z
7. Brousseau P-M, Gravel D, Handa IT. (2018) On the development of a predictive functional traitapproach for studying terrestrial arthropods. J Anim Ecol. 2018;87:1209–1220. https://doi.org/10.1111/1365-2656.12834