Geographic similarities
It is also important to note that differences in the environments of
each of the three invasive ranges may have influenced expansion rates.
In Australia and South Africa, starlings have not expanded to cover the
same area that they have in a comparable amount of time in North
America. In North America starlings spread from New York to Alaska from
1890-1970, which represents 80 years and a rate of 90km/year (Bitton and
Graham 2014). In Australia, starlings rapidly expanded their range into
south-eastern Australia and were in Western Australia by the 1970’s.
However, the center of the continent remains without starlings, due in
part to ongoing invasive species management efforts (Rollins 2001). In
South Africa, starlings spread primarily eastward from Cape Town, and
are now reported only as far north as Kruger National Park
(Berthouly-Salazar 2013; Sulliven, 2009). The regions that starlings
have seen the most range expansion has been into temperate areas.
Interestingly, the starling population in North America is at the same
latitude as that of the natural range between about 40° – 55°N, whereas
the invasive populations in Australia and South Africa occur at about
30° – 35°S (Sulliven, 2009). The arid center of Australia likely
prevented expansion, with the highest temperatures and lowest rainfall
associated with the middle of the country (Jones et al, 2009). These
distinct climate zones may have differentially impacted invasion both
spatially and temporally in each of these three non-native ranges. The
center of Australia is classified as an arid, hot, dessert with
surrounding areas classified as arid, hot, steppe. The same is true for
large areas of South Africa (Beck et al. 2019). On the other hand, the
United Kingdom and surrounding parts of Europe (native-range) are
largely classified as temperate with a hot or warm summer (Beck et al.,
2019). The same classification is used for large portions of the
northeastern United States near the initial introduction of starlings.
This poses an explanation for the rapid and continued expansion of
European starlings in North America, and suggests that the success of
starlings in South Africa and Australia may have required adaptation to
novel climatic conditions (Rollins et al, 2016).