Invasive Species: A
History of How Humans
Modify their
Environment
TX Envirothon Teacher Training
January 19, 2016
Kathleen A. Garland, UHCL
Invasive Species: My definition
A definition: a species of animal, plant, or pathogen is considered invasive if:

it is not indigenous to the location where it occurs;

it is capable of out-competing the indigenous organisms which occupy the
same ecological niche; and

its proliferation causes harm to the local environment and ecosystem
NOT ALL EXOTIC SPECIES ARE INVASIVE!
Historical (and epic) examples of species
invasions from around the world

Rabbits in Australia (gosh, they are cute and fun to hunt!)

Stoats in New Zealand (we need to do something about all these !@#$%
rabbits!)

Starlings in the US (Thank you, Shakespeare, and your loyal devotees)

Crown-vetch (a Penn State introduction for erosion control on highway
embankments)

Eurasian Carp (Wish we could eat what we did back home)

Pigs in Texas
How do exotic species move from one
place to another?

In the examples here, they were deliberately transported by humans.

Why?
Rabbits in Australia

Domesticated rabbits: brought by European settlers as a source of meat

Thomas Austin liked to hunt rabbits. He introduced 24 wild rabbits to his
estate in Victoria in 1859.(http://www.animalcontrol.com.au/rabbit.htm)

What happened?
Stoats in New Zealand
Stoats were introduced into NZ in the 1880s to control rabbits and hares (which were themselves
introduced by man for food and hunting)
What is a stoat?
A small, predatory mammal similar to a weasel
Excellent climbers, runners, and swimmers
Up to 12 young per year
Kill for sport as well as food
Up to 20 kills per night
Why are they a problem in NZ?
Because New Zealand is an island, a number of highly vulnerable bird species, many of them
flightless and ground-dwelling, evolved in the absence of mammalian predators
18 bird species still exist
18 extinct species, including the Moa
Clockwise,from top left
Kiwi
Kea
Kakapo
Takahe
Stoat Predation

It’s easier for a stoat to catch a flightless bird than to catch a rabbit…

Adult birds live on the ground or in trees


They cannot escape by flying

They have no defensive mechanisms

Eggs and chicks in nests are highly vulnerable

Kakapos are extremely slow-moving
NZ conservationists fight a continuous battle to try and preserve these and
other species in the face of a highly efficient predator
European Starlings in the US

Imported around 1890 by Shakespeare enthusiasts

These well-meaning “Bardophiles” attempted to import every bird mentioned in
Shakespeare’s works (including the English sparrow)

He said he would not ransom Mortimer;
Forbad my tongue to speak of Mortimer;
But I will find him when he lies asleep, And in his ear I'll holla 'Mortimer!'
Nay,
I'll have a starling shall be taught to speak nothing but 'Mortimer,' and give it him
to keep his anger still in motion.
-Henry IV, Part I, William Shakespeare
European Starling vs. Boat-Tailed
Grackle (male and female)
Impacts

Urban pests due to defecation

Agricultural pests: crop damage

Transmission of avian and human diseases
Crown vetch

A leafy, flowering vine that prefers disturbed areas

Imported by PSU Agriculture in the 1950’s as an erosion control plant for
highway embankments

Spreads by both seeds and rhizomes

1 plant—70+ square feet in four years

Not subject to parasites or eaten by herbivores

The “perfect” plant for hard-to-vegetate areas

But spreads easily to gardens, fields, and forests
Purple Crown Vetch
photo by Dan Tenaglia, Missouriplants.com, Bugwood.org
Asian Carp
introduced to control algae in aquaculture
Feral Hogs

Escapees from the pigpens; first herd brought with De Soto to Florida in the
1500s

Released for hunting; population surge in TX due to transport and stocking
onto ranches in the 1970s-90s

Extremely prolific breeders

Predators are rare, and limited mostly to piglets

red-tailed hawks and golden eagles; alligators; Turkey vultures; bobcats; coyotes;
mountain lions; possibly black bears
Feral hog
Impacts

Destroy crops, landscaping, trees, dirt roads, stock tanks

Compete with stock and local wildlife for forage

Damage riparian areas and wetlands

Dangerous to encounter: vehicle collisions

Incursion into suburban areas—risk of human/hog interactions
What can we glean from these cases?

Common causes of species invasion



Human-mediated for practical purposes

Food (rabbits, pigs)

Sport (rabbits, pigs)

Erosion control (crown-vetch) or ornamental (many)
Imported as biological controls

Stoats

Asian Carp
Imported as a response to nostalgia for the homeland

Starlings

Asian Carp

Rabbits
Why didn’t these efforts work as we
hoped?

Lack of knowledge of the ecological role of these organisms

Lack of understanding of the control mechanisms present in the native
environment

Lack of understanding of the ecological relationships in the new host
environment

Lack of understanding of the reproductive capacity of these organisms

Overconfidence in our ability to control these populations through hunting
and other food-gathering practices

Lack of monitoring of these populations until they exploded

Many other possible reasons…
What does that mean we need to know
in order to control an invasive?



In-depth knowledge of the characteristics of that species

Maximum size

Means and rate of reproduction

Foods

Natural predators and diseases
Understand that species’ ecological role in its native environment

Position in the food web

Role in the environment (predator, prey, scavenger, etc.)
Understand the ecology of the new environment and how it differs from the
old one.
The final slide—Lionfish—rescued from
aquaria, now coming to a reef near you