How Many Species?

How many species would you expect can be found it a typical suburban backyard? Maybe 50? Or perhaps 100? More? The question is a little vague, so lets try to narrow it down.

There are going to be quite a few factors that affect exactly how many species you are likely to find on a suburban property.

Let’s start with property size. How large is a typical suburban property? Let’s consider the lower end to be multi-story townhouse on 150m2. At the upper end an older style property with perhaps 2,000m2.

We must consider how much of this property is utilised for human needs, i.e. house, patio, driveway, garage, pool, paved areas, etc. These areas typically exclude the majority of species. A townhouse property is likely to be 80% utilised, leaving approximately 30m2 ‘undeveloped’. An older style property may only utilise 10% of the land, leaving up to 1,800m2. The difference between these two will have a significant effect on the number of species likely to be present.

Now consider the form of that ‘undeveloped’ land. Is it a heavily manicured garden consisting of a large patch of lawn with interspersed garden beds filled with exotic plants, a vegie patch and some fruit trees. To our eyes, such a garden may seem to be filled with life. The Honey Bees always pollinating, the vegie patch constantly under attack by various Invertebrate herbivores, the Birds flitting about the trees. But our eyes alone are a poor judge of biodiversity. So much goes unnoticed, either too small to be spotted, camouflaged, or occurring after dark or out of sight.

Or is the garden in a more natural state with some of the original native trees and shrubs. Or some planted local native species. Or even a small patch of degraded remnant vegetation. So many species are critically dependent on specific vegetation and environmental conditions that even a few planted local species can dramatically alter the number of species in the yard.

How ‘structured’ or ‘ordered’ are the garden areas. Does the garden consist of only a few species, perhaps arranged into neat repeating rows. Our attraction to patterns and geometric forms may result in a garden we find appealing, however this doesn’t necessarily correlate with biodiversity. Even where this setup uses native vegetation, the arrangement and limited number of species is likely going to limit the utility for native species.

Are the fallen leaves swept up. Lawns raked. Plants pruned. How about removal of debris like fallen branches, logs and rocks from the yard. While these maintenance activates are considered desirable to keep the garden orderly, these materials are frequently used by native species for food, shelter, nesting material, etc. Removing them also removes the dependent species.

Does the garden consist of one large area, or is it broken up into separate sections. Front yard, backyard, driveway border. Are these areas separated by inhospitable environments. A simple paved garden path isn’t going to deter the Birds in your yard, but to ground dwelling Invertebrates it may represent an impassable barrier. Or at least, a barrier than significantly increases risk.

Do the plants in the garden sprout, grow, mature and seed quickly. How dynamic is the garden. How much maintenance does the garden ‘need’. A slow growing, static garden has limited resources available for species to utilise. The plants are the source of chemical potential energy that animal life requires, and are there to be consumed. More plant growth results in more food to be consumed and a greater number and variety of species present.

A property doesn’t exist in isolation. Many of the species found are likely to reside elsewhere and only visit the garden. As such, the surrounding environment is going to have a significant effect on what type and how many species found. Is the property part of a new housing development where all the local land was recently cleared. Does the property back onto an area of native vegetation, or a creek.

Obviously the local climate is going to be a significant factor in the number of species found. Semi-arid, Mediterranean, wet forest. The more warmth and water, the greater the biodiversity.

How much ‘work’ is put into the garden. In this instance we are considering ‘work’ to be the additional time, energy and resources used to maintain the garden in a state suitable for maximising biodiversity. This may take the form of extra watering in dry weather and feeding the soil with additional nutrients. In urban cultivated environments plants don’t often seed and produce seedlings, or if they do the location isn’t suitable. Extra work is required to replant new seedlings each season. Additional work put into the garden can boost the biodiversity significantly. Such a garden has the potential to maintain biodiversity exceeding that of natural areas.

Exactly what scale of life is considered will also determine the total number of species found. The ability to see and identify the species is key. While a spade full of soil may contain hundred of species of bacteria, these are somewhat beyond identification without dedicated equipment and specialist knowledge. However, they are still present and should be considered as part of the biodiversity.

These 11 factors all come into play when trying to determine how many species you could potentially find on your property. However, not all factors are equal. Some will have a dramatic effect and others may be less critical. The local climate and type of surroundings are likely to be the most significant and unfortunately there often isn’t much that can be done to change these. The size of the property is important, but it’s not something easily changed. To aid in increasing biodiversity within your yard, the best option is to aim for a natural, unstructured, debris filled, connected and dynamic garden.

Now to consider the actual number of species. I have been casually recording species I have located on my property for the past three years. You can see on the chart below how my property aligns with each of the 11 factors. I continue to find new species every week with minimal effort. I have still yet to do thorough investigations of the leaflitter and soil. As of Feb 2022, I have recorded at least 582 species, and uploaded them into my Backyard Biodiversity project on the iNaturalist platform.

These 582 species include 212 Moths, 77 Beetles, 50 Flies, 43 Wasps, 35 Bugs, 32 Spiders, 28 Birds, 20 Introduced weeds, 13 Ants, 8 Butterflies, 8 Cockroaches, 7 Hoppers, 7 Fungi, and many more taxa. This list excludes the 100+ species of cultivated Plants. The full list is presented here. There are still quite a few species I’ve recorded but have yet to identify that will boost this total further. While the rate of additional species discovery has slowed significantly, I expect that 800 to 1000 species is a reasonable estimate for the total number of species to be found.

So consider your property with regard to the 11 factors above, and make an estimate as to how many species are utilising it for food and shelter. Think twice before sweeping, raking, pruning or otherwise altering the garden. Then get out there and start discovering. Don’t forget to upload your sightings to iNaturalist to keep track.