This course investigates the invasive biology of alien and in some cases indigenous organisms. The course content includes definitions; history and globalisation; the human dimension; characteristics; ecology; impacts; management; predictions; restoration; national and international context.

WELCOME TO INVASION BIOLOGY

Welcome

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make regular use of the discussion forum - trade ideas and resolve problems

be sure to submit assignments before the due date - late assignments will not be marked

NB name your assignments using your first name, leaving no spaces eg sallyalienplants.doc

assignments must be typed in aerial font, size 12, using 1.5 line spacing 

check the course outcomes and the study questions at the end of each chapter to gauge your own progress

the educator will check and respond to e-mails daily between 2-4pm and will be online during this time for discussion

the educator will make every effort to mark assignments timeously (within two weeks after the due date) 

COURSE EXPECTATIONS

Course expectations

• Introduced/alien species: Introduced species are those that move into an area from which they don’t originate, and have never previously occurred.

• An invasive alien species has most likely been introduced by human action to an area where it did not previously occur naturally (i.e. not indigenous).

• It is capable of establishing a breeding population in the new location without further intervention by humans,

• Becomes a pest in the new location, threatening the local biodiversity.

• The term invasive alien species is most often applied to plants and larger animals, but less well-known microscopic and microbial species can also be invasive.

Definitions

• The term invasive usually implies harm, either actual or potential. This harm may be manifested in ecological, economic or social impacts.

• Some indigenous species may become invasive under certain conditions, such as environmental change. This change often occurs as a result of human influence• e.g. Pied Currawongs of Australia

expanded their range drastically in the 20th century because of human changes to the landscape causing large declines in populations of smaller birds that were being preyed upon by the Currawongs. A good local example is the Hadeda Ibis

Definitions

There is a lot of confusion in the scientific literature, policy documentation and internet resources around what exactly defines an invasive species.

The need for a definition for invasive alien species resulted from a need to control or manage them.

Many terms have been used interchangeably to describe the same concept (e.g. non-indigenous, exotic, alien) and other terms used to describe unrelated concepts (e.g. invasive, naturalized, imported).

These varying definitions have caused (and continue to cause) confusion and controversy.

A clear understanding of the key concepts in biology, ecology and biogeography relating to invasion of alien species is thus essential.

THE NEED FOR DEFINITION

The need for definition

Most confusion has been concentrated on the word invasive (Richardson et al, 2000a). Most widely used definitions include statements relating to two or more of the following:

1. The species’ alien status 2. Ability or potential to establish themselves and

overcome barriers to reproduction, dispersal and population increase in the new environment

3. The ability or potential to cause harm to the environment and/or human health

Are aliens from outer

space?

CONFUSION

Confusion

Many species have been introduced to new environments over the centuries, and very few have become invasive.

It is estimated that of the species introduced to a new environment:

10% become established, of these 10% become invasive, and of these 10% cause substantial damage.

This is referred to as the ‘tens rule’ (Wiliamson and Fitter, 1996).

THE TENS RULE

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The tens rule

a) BIOLOGICAL/ECOLOGICAL PRINCIPLES:

These definitions are objective and have measurable criteria.

“Invasive species are a subset of naturalised species that produce reproductive offspring, often in very large numbers, are able to disperse considerable distances from parent populations, and thus have the potential to spread over a large area” (Pyšek et al, 2004).

Note that this definition has no implied impact.

TWO MAIN GROUPS OF DEFINITIONS OF ‘INVASIVE’ EXIST, BASED ON DIFFERENT PRINCIPLES:

Biological/ecological principles

b)ANTHROPOCENTRIC (HUMAN-CENTERED) PRINCIPLES:

These definitions focus the attention of policy

makers on the biggest impacts:

“Invasive alien species are non-indigenous organisms that cause, or have the potential to cause, harm to the environment, economies, or human health” (Global Invasive Species Programme).

Many impacts are however not readily measurable, or if they were then the problem would arise as to applying a monetary value.

This definition has however been widely adopted including Executive Order 13112 of 1999, signed by President Clinton.

Anthropocentric principles

Reliance on human interactions for definitions results in them often not being consistent, especially when impacts are both beneficial and detrimental, and species may be considered a nuisance wherever they occur simply because they are a nuisance elsewhere (Colautti and MacIsaac, 2004).

ANTHROPOCENTRIC DEFINITIONS - THE PROBLEM

http://www.iatge.de/index.html?aktuell/veroeff/ie/lehner92c.html

Invasion ecology is the study of how organisms spread into habitats to which they are not indigenous (Alpert et al, 2000)

An invasion is the geographical expansion of a species into an area not previously occupied by it (Vermeij, 1996)

Indigenous species (native): originated, evolved or arrived (from an area in which they are indigenous) in a given area without human intervention

GENERAL DEFINITIONS (Pysek et al, 2004) unless otherwise stated:

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General definitions

• Alien species (exotic, introduced, non-native, non-indigenous): taxa in a given area whose presence there is due to human involvement, or which have arrived there without the help of people from an area in which they are indigenous. Taxa can be alien to any definable geographical area, e.g. continents, islands, bio- or ecoregions, or any political entity (e.g. countries).

Human involvement in this case does not include habitat changes, global warming, etc.

GENERAL DEFINITIONS cont.

Carcinus maenus, the European Green Crab, was introduced to North America in the 1800's. This predator now ranges from Nova Scotia to Delaware.Photo Credit: Paul Erickson

General definitions cont.

Cryptogenic species (mostly microscopic taxa or those with poor taxonomic resolution): species that are not demonstrably indigenous or alien (Carlton, 1996).

• Note that the term ‘Cryptogenic’ has been mistakenly used to mean an introduced species whose original home is not known, i.e. of unknown geographic origin, even though it is clearly recognized as non-indigenous

GENERAL DEFINITIONS cont.

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General definitions cont.

• Casual alien species: taxa that may flourish and even reproduce occasionally as aliens outside cultivation or captivity in an area, but that eventually die out because they do not form self-replacing populations, and rely entirely on repeated introductions for their persistence

GENERAL DEFINITIONS cont.

The Chaffinch was originally introduced to the Cape from England by Cecil John Rhodes. A small population survives in the vicinity of Tokai forest, but numbers seem to be declining.

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General definitions cont.

• Naturalized species (established, feral): alien species that sustain self-regenerating populations for a reasonable period of time, unsupported by and independent of humans

• Feral species (usually mammals, birds and fish, also insects): species that have lapsed into a wild form from a domesticated one

GENERAL DEFINITIONS cont.

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General definitions cont.

• Invasive species: a subset of naturalized species that produce reproductive offspring, often in very large numbers; capable of dispersal or movement over considerable distances from the parent populations; have the potential to spread over a large area

• Note: Organisms should be labelled ‘invasive’ with reference to a given geographic locality. Organisms that spread previously, but do not spread currently because the total range of suitable habitats and landscapes have been occupied, should still be termed invasive because local eradication will undoubtedly lead to re-invasion.

• Note: This definition infers no connotation of impact, although many invasive species do have impact.

GENERAL DEFINITIONS cont.

General definitions cont.

• Transformers (plants): a subset of invasive plants (not necessarily alien) that change the character, condition, form or nature of ecosystems over a substantial area. Several categories of transformers may be distinguished: excessive users of resources (water, light, oxygen), donors of limiting resources (nitrogen), fire promoters or suppressors, sand stabilizers, erosion promoters, etc.

GENERAL DEFINITIONS cont.

• Pests (harmful, problem, noxious): taxa (not necessarily alien) that grow or live in sites where they are not wanted and which have economic or environmental impact or both. For plants, the term ‘weed’ is used.

GENERAL DEFINITIONS cont.

General definitions cont.

Taxonomic resolution i.e. whether the species evolved or migrated into the area without human intervention. In the case of alien species, they have been moved to an area through direct or associated human activity. It is not always easy to determine if a species is indigenous or alien especially if their taxonomy is not resolved e.g. smaller organisms such as viruses, bacteria, fungi, algae, protozoa, arthropods and plankton. Those species without defined taxonomy are therefore labelled as cryptogenic

DIFFICULTIES IN DETERMINING WHETHER AN ORGANISM IS INDIGENOUS OR ALIEN:

Taxonomic resolution

Gene level invasions (covered in Chapter 6) and the spread of alien genotypes (species with different genetic composition but similar physical attributes to the indigenous species) within ranges of the indigenous species. This leads to hybridisation between the indigenous and alien species, complicates the classification of a species as indigenous or alien. Genetically modified versions of indigenous organisms are often listed under non-indigenous species

The plant on the left side of the photograph is a natural form of Arabidopsis thaliana, while that on the right side is a genetically engineered variant whose leaf shape has been modified through the insertion of a homeobox gene.

Gene level invasions

• Geographic scale: When organisms encroach on habitats in which they were not previously recorded, they can be termed colonizers (ecological perspective), invaders (biogeographical perspective), or weeds (anthropogenic perspective)

• Space and time: A species may well be invasive at one locality at one time, but not invasive under other situations

DIFFICULTIES IN DETERMINING IF AN ORGANISM IS INDIGENOUS OR ALIEN:

Indigenous or alien?

Although basic processes of geographic spread and increase in range is essentially the same for both alien and indigenous species, alien species have certain attributes that make them need further and closer management attention.

The major differences between indigenous and alien species

are that indigenous species have co-evolved natural enemies, predators and symbiotic relationships, whereas aliens are usually without any of these. Alien species are therefore at an advantage since they have

left all their natural predators behind (Richardson et al, 2000b).

ARE INVASIONS BY ALIENS DIFFERENT TO THOSE BY INDIGENOUS SPECIES?

Are invasions by aliens different?

Links to other chapters

I hope that you found chapter 1 informative and that you will enjoy chapter two!

Chapter 1 Definitions

Chapter 2 History, globalisation and GMOs

Chapter 3 The human dimension

Chapter 4 Pathways of introduction

Chapter 6 The ecology of biological invasions

Chapter 5 Characteristics of invasive alien species

Chapter 7 Impacts of invasive alien species

Next

Chapter 8

Chapter 10

Chapter 9

Chapter 11

Chapter 12