Teacher background information

This elaboration allows students to examine the impact of invasive species that have been imported through human activity such as agriculture. Students learn about how this is impacting upon important food webs of local ecosystems, which subsequently impact Aboriginal and Torres Strait Islander communities who depend on these ecosystems for cultural continuance, food and medicine. 

This elaboration also provides students with opportunities to deepen their understanding of food chains and food webs as a way to represent interactions between organisms in ecosystems.

European colonisation has resulted in the introduction of numerous foreign plants and animals which continue to have significant impacts on traditional Aboriginal and Torres Strait Islander peoples’ resource access and cultural practices. Invasive species are those that are introduced to a specific location to which they are not native, and which have multiplied to the point where they cause significant interruptions to the environment. These introduced species tend to spread rapidly and cause widespread damage. This has implications for environmental, agricultural, cultural and other social resources. Two critical examples of nationally significant invasive species that were introduced to Australia for European agricultural reasons are the cane toad (Rhinella marina) and gamba grass (Andropogon gayanus). 

Native to South and Central America, the cane toad was introduced to Australia in 1935 to control pest scarab beetles in Queensland’s sugarcane crops. The cane toad population quickly established itself as a pest, spread throughout Australia’s northern regions and is currently moving westward at an estimated 40 to 60 km per year.  

The introduction of cane toads has severely interrupted the food chains and food webs of the ecosystems they have invaded. As toxic and prolific invaders, cane toads have impacted on the populations of native species groups such as quolls, monitor lizards, snakes, fish, turtles, crocodiles, birds and invertebrates. Some examples of species that have been impacted by cane toads are the flood-plain goanna, barramundi, black bream and catfish, long and short-necked turtles, freshwater and salt-water crocodiles, some aquatic invertebrates and even some bird species, such as pelicans and herons.  

Research suggests that cane toads are having a significant cascading effect on trophic levels. For instance, it has recently been discovered that cane toads have a negative impact on the population of a grain-eating bird despite these two species not being directly linked in the food web. The populations of many predator species have also been adversely affected by cane toads.  

Being part of the food web themselves, this also has a subsequent effect on Aboriginal communities that are partially or solely dependent on the availability of these species as a source of food and other resources. For example, the yellow-spotted monitor or floodplain goanna is an important source of meat for Aboriginal people living in remote communities in northern Australia where access to butchers or an affordable meat supply is limited. The population of floodplain goannas has been severely impacted by cane toads, and in some areas localised extinctions have been recorded. This is having a serious impact on the availability of meat resources in these communities. 

First Nations’ organisations such as the Yugul Mangi Aboriginal Ranger group are working with government departments to identify long-term cane toad management strategies. Some approaches include increasing awareness of the impact of cane toads, exploring control management options with various stakeholders and working on a feral animal plan for the South eastern Arnhem Land Indigenous Protected Area. 

Originally from the tropical and sub-tropical savannas of Africa, gamba grass was introduced into Australia in the 1930s as pasture for cattle. In the 1990s gamba grass was identified as an invasive species, with potentially devastating impacts on native biota. Considered one of the fastest spreading invasive species in the world, its spread in the Northern Territory and North Queensland is having a significant impact on various ecosystems.  

Weeds such as the gamba grass can have a range of impacts on natural habitats including competing with native plants for resources, altering soil-nutrient cycles and intensifying bushfires by carrying higher fuel loads. In addition, gamba grass can also create a monoculture by directly competing with and replacing native plant species and by indirectly increasing fire intensities. Gamba grass grows prolifically once established as it grows taller than native grasses and forms dense clusters, inhibiting the growth of native grasses and replacing native species. This species is having devastating impacts on the food chains and food webs of the ecosystems it is invading and is directly reducing culturally significant food sources for many Aboriginal communities. The abundance of gamba grass has also restricted access to sites of cultural and spiritual significance for some Aboriginal and Torres Strait Islander communities. 

As a tussock grass, gamba grass can produce a biomass up to 10 times that of native plants and tends to increase fire intensities by a factor of 3-8. When gamba grass burns, it creates a more intense and hotter fire than native grasses resulting in fires that are more difficult to control or extinguish. When native plants and their seed banks are destroyed in these intense fires, soil erosion can occur. This can inhibit the natural regeneration processes of native species due to an increase in waterway sediment. Gamba grass also impacts the food web of its surrounding ecosystems by altering the structure of native vegetation and having the potential to transform woodlands into treeless grasslands. Moreover, it has been known to reduce the diversity and abundance of reptilian species in eucalypt woodlands.  

The Australian Government recognised the threat posed by gamba grass in 2009 when it listed 'Ecosystem degradation, habitat loss and species decline due to invasion of northern Australia by introduced gamba grass, para grass, olive hymenachne, mission grass and annual mission grass' as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). In 2012 it was classified as a Weed of National Significance (WoNS). This weed has such profound impact that the world heritage-listed Kakadu National Park is also at significant risk. 

Local Traditional Owners such as those in the Rum Jungle mine site in northern Australia are working in collaboration with government agencies to mitigate seed dispersal by means of seed eradication and foliage spraying. This is not only an attempt to control the spread of gamba grass but to reduce impacts on vulnerable ecosystems. 

The national response to these introduced species has resulted in the need to include and collaborate with Aboriginal and Torres Strait Islander peoples to address the threats and mitigate the environmental impacts. The extensive knowledge and expertise held by Aboriginal and Torres Strait Islander peoples regarding the delicate and complex interrelationships of food chains and food webs within those ecosystems places them as critical experts and partners in governmental efforts to restore environments damaged by introduced species.  

Students will gain an understanding of how interactions between organisms can be represented by food chains and webs, as well as the extent to which these can be affected by human activity. Additionally, they will have opportunities to learn about how invasive species have impacted on food webs which many Aboriginal and Torres Strait Islander communities rely on for food and other resources such as medicine. Students can also investigate how Aboriginal and Torres Strait Islander peoples have responded to these impacts in an effort to restore traditional ecosystems.