INNS

7-spot ladybird

Which is Invasive?

Dandelion

Harlequin ladybird

All of them!

Depending on where you are in the world.

Japanese knotweed

European starling

Canada Goose

Characteristics

Most non-natives don’t survive (just ask a gardener), or maybe they become naturalised; but some are super invasive. Why?

Because these species lack an evolved relationship with factors (biotic or abiotic) that would ordinarily check their population growth.

Some species have characteristics designed for a limited environment, so when the limits are gone, they out-compete.

Example: the Spanish Slug

Probably the slug you’ve seen the most

Introduced to UK accidentally in top soil for gardeners

Home range is arid – not great for slimy bois. So, they lay around 800-900 eggs in one go, in the hopes that 100 will remain wet enough to hatch. Why is this an issue in the UK?

Because in UK, we Do Not Lack Rain.

So, all 800-900 hatch.

Gives a huge competitive advantage over native slugs

Probably the slug you’ve seen the most

Introduced to UK accidentally in top soil for gardeners

Home range is arid – not great for slimy bois. So, they lay around 800-900 eggs in one go, in the hopes that 100 will remain wet enough to hatch. Why is this an issue in the UK?

Species to Species

Other INNS might just lack an evolved relationship with another spp that would normally keep them in check.

What could this relationship be?

Other INNS might just lack an evolved relationship with another spp that would normally keep them in check.

What could this relationship be?

• No suitable predators (either through simple food web mismatch, or because the predator cannot breach defences)

• No suitable defences in a host spp, in cases of mutualism/parasitism

• No suitable defences in a prey spp, so overabundance of food

• Too high an overlap with competitors when getting resources

Example: the Asian Giant Hornet

Like all hornets, they’re very good killers.

In their native range, honeybees have a natural resistance – when a hornet enters the hive, the bees swarm it en masse and vibrate to heat it up. The hornet cooks in the bee ball.

But European honeybees don’t know how to do this, so they get mown down and the hive slaughtered.

Stage One: Arrival

Both intentional and accidental (these days mostly accidental); but also both anthropogenic and natural.

The rat is now a global species thanks to trade ships in the ancient world – this was not intentional.

But, plenty are! Can you think of examples?

Both intentional and accidental (these days mostly accidental); but also both anthropogenic and natural.

The rat is now a global species thanks to trade ships in the ancient world – this was not intentional.

But, plenty are! Can you think of examples?

Agriculture:

• Food plants
• Fibre plants
• Livestock

Colonisation

• Pet Releases
• Domestic pets (e.g. the cat)
• Acclimatization Societies (hello colonialism)

Natural Vectors

Dispersal methods are commonplace among many species; primarily plants, but also curve balls like fish, and lots of insects

Wind and water currents both transport seeds, insects and others from area to area about the planet

Migratory birds are a huge dispersal vector, for seeds and fish eggs and the like

And driftwood! Hitchhikers

Anthropogenic Vectors

Much, much bigger. Earliest records are probably Roman; catnip, rabbits, chestnuts etc to UK, for example.

But, huge explosion during Victorian era. Partly intentional with the invention of Acclimatization Societies, but partly accidental - people were fascinated by species turning up at ports (ballast).

1890, Nevada - experiment station official gave pamphlets on an invasive plant to landowners. To make sure they could ID it, he included a mature plant with each, including seeds.

It went as well as you're imagining.

Stage Two: Establishment

Not every new invader becomes established!

Habitat to which the invader is transported requires resources for survival and reproduction

Timing of invasion must be appropriate for the invader life stage

The introduced population must be sufficiently large

More individuals, better invasion success - Allee effect

More introduction events, better invasion success

Allee Effect

Normally, birth rate (b) increases as populations decrease; however, in very small populations, the birth rate may decline due primarily to difficulties in mate location (or inbreeding)

This means a population needs a threshold density to persist into “oh shit” territory.

Introduction events can simply be more visitors – shoes, tyres etc all increase chances.

Stage Three: Spread

Some factors increase spread:

• Changing land use pattern (habitat changes attract/expel species)
• Travel/Trade
• Climate change
• Lack of natural population regulation (no predators, for e.g.)

Why?

The Costs

Potentially, enormous costs environmentally, economically and socially

An increasing rate of accidental introductions, e.g. North America:

Up to 1985:

• Approx. 5000 invasive species established
• All taxa (animals, plants, microbes)

From 1985-2000:

• 6825 interception records of alien insects in wood products in US alone

So, introductions are increasing: why?

Travel, and poor biosecurity.

All forms:

• Freight containers
• Encrusted animals/plants on boats
• Diseases, parasites of pets
• Shipping…

Shipping...

Major source of marine and fresh water introductions

Water-filled ballast tanks (water that is taken in or let out of the ship to keep it balanced as cargo is loaded and unloaded.)

Filled at port of origin, discharged at destination

Meanwhile, the socioeconomic impacts can be profound in developing countries like Ethiopia. Can threaten biosecurity, and therefore food/resources.

Coupled with less education, meaning INNS are harder to spot.

Grey Squirrel (Sciurus carolinensis)

Introduced in the 1870s from N America, because rich land owners thought they looked exotic

Not actually a competition issue – it’s disease.

Greys carry “squirrel pox”, a flesh-eating virus that they are immune to. Reds are not, and die in 15-18 days after contracting it.

Research in the last five years by Dr Emma Sheehy has found that reintroducing native pine martens causes grey populations to plummet, and allows reds to bounce back.

Japanese Knotweed (Fallopia japonica)

Imported as a pretty garden plant, but it escaped – first wild plant recorded in 1886.

And then… nothing, for 100 years.

This is because it cannot breed. Knotweed in the UK is a single female clone. Instead, it reproduces when roots are disturbed by sending up new stems from the root pieces.

It became invasive, therefore, thanks to poor biohygiene practices in the construction industry.

estimated annual cost of managing this species in Great Britain is £165 million every year

Estimated eradication cost: £1.65 billion

Rhododendron (Rhododendrum ponticum)

Introduced by gardeners in 1763

Not all species invasive, but R. ponticum is, and it is THE WORST

Spreads fast and thick. Shades out native trees and understorey species, but also a disease risk

Partly because of altered abiotic environment – by filling the understorey they block air flow, so fungi proliferate (e.g. honey fungus)

But also because, as a shrub, they themselves can become disease vectors (e.g. Phytophthora). Trees already weakened, so more susceptible.

Exercise

Let's think about management!

You are the ranger of a small island, which is having problems with two invasive species. What management techniques would you put in place to control each (i.e. minimise impacts/eradicate)?

For the sake of realism, let's say your monetary resources are small.

Species 1

Size: 150-250 mm in overall body length.

Weight: maximum of around 1 kg.

Behaviour: Nocturnal.

Reproduction: 2 litters per year, with between 4-7 per litter.

Diet: Insectivorous.

Key prey items: slugs, snails and larger insects, but will eat almost anything, including eggs, lizards, amphibians, baby birds.

Species 2

Size: 460mm not inc. tail.

Weight: 4-5 kg.

Behaviour: Nocturnal but have crepuscular tendencies.

Reproduction: up to 3 litters per year, with between 1-6 per litter.

Diet: Carnivorous.

Key prey items: small mammals, birds, reptiles, amphibians.

Species 1 - Hedgehogs!

Very invasive in New Zealand and, for a while, the Outer Hebrides

Introduced as biocontrol, but then they just started eating the chicks and eggs of ground nesting birds

Outer Hebrides - small island, so rounded up and released on mainland

New Zealand - culling, and exclusion fencing.

Meanwhile, in mainland UK they are struggling with falling numbers.

Species 2 - The Cat

Yes, Moggy is a killer. A very prolific hunter of native fauna, in fact.

The cat is considered to be one of the top causes of species decline and extinction, second only to rodents, and is linked to 63 modern day extinctions.

Introduce cat-specific disease to endangered populations of Florida panthers and the Scottish wildcat, the latter of which they also interbreed with [feline leukaemia]

Globally there are over 600 million cats, with an estimated 100 million of these being feral. Recent studies suggest that in the US alone feral cats alone kill 2.4 billion birds and a around 12.3 billion small mammals; while researchers in Australia believe over a million reptiles per day are consumed by cats (in one case they found 40 individual lizards in a single cats stomach!)

Cat Control

Best method found is TNR - trap, neuter, release; breaks the breeding cycle and reduces the number of death threats set to practicioners (yes, really). BUT, this does not help immediately, because still releasing them.

Here's the problem: humans. It's very much within our cultural ideals of cat ownership to let them roam free outdoors, with many feeling it's "cruel" to keep them in. So, pet cats are the problem.

What's needed is a cultural shift to the indoor cat, same as the indoor dog.