ECB Threats

ECB are believed to have a low dispersal capability (<200m) and mapping of habitat where they occur shows that they only occupy between 5-26% of available habitat. These factors makes them extremely vulnerable to threats. The theats they face vary with each remnant and/or region they occur in. For example in the Wimmera remnants are very small and isolated in a sea of agricutlure, where they have a high perimeter for weed and pest invasion. Whereas in the north central they occur in small patches within large tracts of national parks where weeds and pests are fewer but the risks from planned burns are siginicant.

Threats have been documented in the national Conservation advise (Threatened Species Advisory Committee, 2016) and summarized here.

The major cause of Eltham Coppr Butterfly decline has been loss of habitat due to agriculture and usrban expansion (Vaughan, 1988).

Land clearing/habitat alteration. This has caused fragmentation and loss of habitat, especially in urban areas due to subdivision, roadworks and building construction (Threatened Species Advisory Committee, 2016).

Urbanisation is also an increasing threat to the Bendigo and Castlemaine (Threatened Species Advisory Committee, 2016) from habitat degradation caused by: trampling, weed invasion, changes in hydrology, trail and mountain bike riding, haphazard creation of unplanned tracks etc.

Planned burns are a major threat in north central Victoria, particlulary when populations are in Asset Protection zones (APZ’s) and therefore burnt to 80% fuel reduction every 5 years. Planned burns and uncontrolled fires: The effects of fire on habitat and survival of the Eltham copper are complex. Slashing and burning of vegetation as preventative measures for wildfires is cited as a direct threat (Threatened Species Advisory Committee, 2016).

Especially in middle to late summer, when fires would destroy adults, eggs, and plants, which would remove the larval food source and adult oviposition sites (New et al. 2000). However, an appropriate fire regime that maintains open habitat and facilitates regeneration of the larval foodplant may be an important management tool for sustaining butterfly populations (New et al. 2000). (Threatened Species Advisory Committee, 2016)

Other factors identified as posing a threat to existing vegetation include degradation of habitat by adverse human impacts, weed invasion and wildfire (Webster, 1993).

Woody weeds such as Cape broom (Genista monspessulana), radiata pine (Pinus radiata) and blackberry Rubus fruticosus) have the potential to outcompete Bursaria spinosa (Threatened Species Advisory Committee, 2016).

Grazing. Grazing of newly germinated larval food plants by rabbits has the potential to significantly reduce the number of juvenile Bursaria plants available to the ECB (Threatened Species Advisory Committee, 2016).

Genetic Isolation:

ECB exists as a meta-population.  Metapopulations are populations of subpopulations within some defined area, in which dispersal from one local population (subpopulation) to at least some other habitat patches is possible. That is there are many small colonies of ECB peppered throughout an area which allows ECB to move around according to availability of favourable resources and survive as these resources change spatially over time and season. Local extinctions of sub populations can be replaced by nearby populations when conditions prevail.

It is very important for species to disperse to new unoccupied habitats for the advent of new populations. The genetic effective size of a metapopulation is affected by the carrying capacity of the habitat patches, the rates of extirpation and recolonization, the number and source of the founders, the number of local populations, and the rate of gene flow between patches.

When ECB populations become isolated from the meta-population structure, they are at risk of no longer being replaced which leads to genetic drift.  both Wimmera populations are small and isolated populations surrounded by housing development and farmland. Translocation of butterflies from healthy populations to isolated ones may help build genetic resilience before they are lost.