Structure, cover and shelter : why complexity matters to promote biodiversity?

'Forest floor' painting by Isabella Kirkland (https://www.isabellakirkland.com/forest-floor)

This week has marked an important milestone for me: my first ever lecture! 

Apart from maybe talking too fast at times, I seemed to have captured at least some students attention, which ,as a first timer , I can be happy with. Hopefully i imparted some knowledge, sparked some curiosity and inspired some young minds (a girl can dream, right?).
I think you are wanting to know what was my lecture about? 
I introduced the students to the wonderful world of ‘Habitat complexity!’. 
And why should I teach about that? 

,I will let you in on a little  truth: much of the surrounding natural environment is somewhat structurally complex. By structurally complex I mean that something is 'rough'. To give you concrete examples, we can observe complexity on small scales (think of mineral crystals or  snowflakes), other at medium  scales (an hedge for example, or a tree) at large scales (a tropical forest, a coral reef), but even larger (a delta system, with its intricate water patterns or even mountain ranges when you look at it from the window of a plane). I bet, you can go outside and identify plenty of things that can be considered complex as anything that is opposite to 'flat' and 'featureless'. 

For example, let's take a look at (or imagine)  a natural patch of grass and you will see many grass species and wild flowers with different structures (thin, thick, hairy, spiny, tall, short...). You will have denser patches, sparser areas, softer sediment and coarser rocky parts. Look under the soil (or use your imaginary shovel) and you will notice a plethora of roots of all shapes and sizes. This is a classic example of a complex habitat. It could be just in your backyard. But maybe you are one of those choosing to have a perfectly mowed lawn, with turfy (maybe artificial?) grass spread homogeneously.. I don't judge, but I hope that you will reconsider after reading this
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Let me start with a basic introduction on why all of this 'complexity' is important.
There are some basic needs that are shared across species:  space, nutrient, safety. 
Yes, this is also what we, as humans, need. That is why we build houses (safety), high up in the shape of skyscrapers in densely populated areas (space!) and why we need yet more space to cultivate in order to produce enough food to sustain us all. 

Now, imagine we are an insect: we need to find something to eat (maybe some grass to munch on), but at the same time we need to hide from the bird flying up in the sky that is looking for us, and well, we need to make sure that there are not so many others crawling around that we don't fit on the ground anymore, and we need to make sure that there is some space so we can find our favourite grass to eat without getting too lost in a thick forest!  
What would be the ideal habitat for such an insect?

You guess it: an area with some high grass that can shelter it from the flying predator, maybe somewhere to climb up in case of a lower down predator, somewhere without too much competition (so lots of nice grasses) and some lower fronds so it is easy to navigate and the space does not get filled up too quickly.

What I am saying is that nature, in order to be functioning in an optimal way, needs a variety of structures! The more, the merrier, and complexity is a measure of just that! 

The importance of complexity can be translated to many other habitats, such as forests (monocrops are not great), saltmarshes, rocky areas, the seabed (think coral reefs...!)
Unfortunately, the complexity in these places is under threat. 
For example: you may know from the newspapers that climate change is leading to the loss of coral reefs. What you may not know is that the corals create complexity that other species need, and that this is creating a negative feedback which is promoting faster rates of disruption by changing how other species interacts and facilitating the growth of fast species like turfing algae (if you are a gardener you may relate this to pesky weeds!)

However, when we think of threats, climate change is not the only culprit. There are, unfortunately, other ways in which we are making ecosystems 'simpler'. For example, think of rapid urbanization that many areas are experiencing: this means replacing natural habitats with simple and flat man made products (like concrete!). And yes, you can somehow engineer these to make them more complex. There are some studies done in the marine world, and yet the same concepts that apply to marine system can also apply to land. For example, if you concrete your garden,  or keep the grass too short (or maybe use fake turf on it..). 

While we might not be able to stop complexity loss st the big scale (yet) there are a few things that we can do to stimulate complexity and prevent further habitat degradation and loss of species at the small scale, which may help the bigger scale too! 

1. stop cutting your grass. Maybe this is unreasonable (who wants a jungle in their yard?) but if you can, aim for a more natural approach. Maybe leave a part of your garden wild? 
2. Think twice before paving. If you are adding any concrete, think about what natural space you are replacing. Does it have any specifics that are not replicated anywhere else in the nearby areas? Can you recreate these situations elsewhere? Can you leave half uncovered?
3. Reconsider how to build. Some birds really like to nest in old buildings because the roofs provide holes for shelter. Can you add something to replicate that in your new building?
4. Insect hotels are a thing! And they can be pretty - maybe have a go st building one?
5. Plant wild ‘pollinator friendly’ seeds. I have added some at the edges of my allotment plot and they are also pretty! 
6. If you are a boat user - think about where your anchor drops! Seagrass beds are a common Anchorage but they can suffer from being uprooted! 
7. Make good food choices. Think twice about things coming from the sea - avoid buying seafood that comes from trawling fisheries, they can destroy large areas of seabed and take up unwanted things..

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