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What is this?

Who misplaced what and why did this displace something else? Well, this is a site about ecosystem integrity and stability and what impact human activities have had.

The misplaced are species introduced by human activity - deliberately or accidentally, directly or indirectly.

The displaced are the species of organisms which are driven out by changes induced by the intruding species.

The site  will explore these impacts through the use of case studies, which will tell the stories of misplaced and the displaced and how this plays out in ecosystems.

The site  also includes a glossary for technical terms and a suggested reading list for those who want to know more.


Why should I care about this?

If you would like a refresher on ecosystem basics, please see Core information on biodiversity (will open in a new tab).

Your life literally depends on continued existence of ecosystems. The air you breathe, the water you drink, the food you put in your mouth all come from ecosystems. The earth provides our resources but recently we have been overstressing the ecosystems of earth, damaging them and  rapidly rendering them not fit for for purpose. This, by logical extension, damages humans and the human economy. If nothing else, sheer self interest dictates that we find ways to lessen the stressors and keep ecosystems from catastrophic decline.

The stressor we are going to examine in detail is the introduction of new invasive organisms into existing ecosystems.

Factors determining ecosystem stability

The stability of ecosystem is dependent upon the

A. The interdependence and interactions between the organisms forming the community

e.g. food webs and other types of interaction


B. Maintenance of the abiotic factors within a range

Abiotic parameters will fluctuate seasonally and no two years will be exactly the same, but overall these factors will fall into a stable range. Without human intervention, climate changes have, in the past,  been gradual, altering over geological time scales, allowing species time to adapt.

Stability Unravelling

Biodiversity loss refers to the reduction of biodiversity due to displacement or extinction of species. The loss of a particular individual species may seem unimportant to some, especially if it is not a charismatic species like the koala or the rhinoceros.

However, the current accelerated extinction rate which is 500 to 1000 times higher than the rates experienced before human intervention means the loss of tens of thousands of species within our lifetimes. This loss of ecosystem members has exposed previously stable systems to a high risk of instability and chaos.

So where does the spanner come into it?

It is not that ecosystems never change. Ecosystems evolve over time by succession to form what is know as a climax community, which is the most stable sustainable assemblage that can be supported by the abiotic factors present.

One of the many ways in which humans upset this balance is the introduction of species that have not evolved in this ecosystem. Humans bring about these changes over very short time spans. This may have been done deliberately or incidentally as a consequence of ignorance or carelessness. No matter how it happens, it can replace or disrupt native species and destabilise the entire system. Invaders can cause a trophic cascade which is the technical term for "who is eating who" to go out of whack.

The International Union for the Conservation of Nature considers invasive species to be the second most significant threat to global biodiversity after habitat loss.

The National Wildlife Federation (USA) claims that approximately 42 percent of threatened or endangered species are at risk due to invasive species. 1

Invasive species often have very efficient reproductive strategies that allow its numbers to balloon. Also  introduced species can become invasive when they  lack predators and/or pathogens in the new environment, hence its numbers are not kept in check as they would be in their own ecosystems.

characteristics of invasive species
characteristics of invasive species

Note that research into invasive species is very uneven with respect to taxonomic groupings, so this pie chart may need to be revised if new findings come to light. Some invasions e.g. cane toads in Australia, brown tree snakes in Guam tend to receive publicity and therefore funding for research.  Unfortunately, in this case, what we don't know can hurt us and there is an urgent need to investigate a wider range of lesser known species.

% of invasive species in each grouping of organisms

Different ways that the invasive species do damage

According to the IUCN, the different types of damage are are:

(1) Competition the alien taxon competes with native taxa for resources (e.g. food, water, space), leading to deleterious impact on native taxa.

(2) Predation the alien taxon predates on native taxa, either directly or indirectly (e.g. via mesopredator release), leading to deleterious impact on native taxa.

(3) Hybridisation the alien taxon hybridises with native taxa, leading to deleterious impact on native taxa.

(4) Transmission of disease the alien taxon transmits diseases to native taxa, leading to deleterious impact on native taxa.

(5) Parasitism the alien taxon parasitizes native taxa, leading directly or indirectly (e.g. through apparent competition) to deleterious impact on native taxa.

(6) Poisoning/toxicity the alien taxon is toxic, or allergenic by ingestion, inhalation or contact to wildlife, or allelopathic to plants, leading to deleterious impact on native taxa.

(7) Bio-fouling the accumulation of individuals of the alien taxon on wetted surfaces leads to deleterious impact on native taxa.

(8) Grazing/herbivory/browsing grazing, herbivory or browsing by the alien taxon leads to deleterious impact on native plant species.

(9) (10) & (11) Chemical, physical or structural impact on ecosystem the alien taxon causes changes to either: the chemical, physical, and/or structural biotope characteristics of the native environment; nutrient and/or water cycling; disturbance regimes; or natural succession, leading to deleterious impact on native taxa.

(12) Interaction with other alien species The alien taxon interacts with other alien taxa, (e.g., through pollination, seed dispersal, habitat modification), facilitating deleterious impact on native species. These interactions may be included under other impact mechanisms (e.g., predation, apparent competition) but would not have resulted in the particular level of impact without an interaction with other alien species.

Credit : IUCN EICAT Categories and Criteria (2020) reproduced for non-commercial purposes.

Dig Deeper


  1. The National Wildlife Federation []
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