Urban reptiles at risk from arsonists


Urban areas (i.e. towns, cities and their suburbs) contain around half of the world’s human population and Australia is one of the most urban countries on Earth, with 89% of Australians living in urban areas.

Percent of total population living in urban areas by countries. Source: http://kff.org/global-indicator/urban-population/#
Percent of total population living in urban areas by countries. Source: http://kff.org/global-indicator/urban-population/

The world’s population, and hence urban areas, are growing at an increasing rate globally and it is estimated that by 2030 urban land cover will increase by more than 1.2 million km2.

Urbanisation leads to large changes in the composition of native plant and animal communities and global estimates have found that urban areas retain on average only 8% of their original bird fauna and 25% of their plant species.

Native animal populations suffer from urbanisation due to habitat clearing and fragmentation, competition and predation from introduced species, and genetic effects that reduce population viability. Increased isolation of habitats and disrupted dispersal ability lead to an increased risk of local extinction from stochastic events such as fire or disease.

In this blog post I am going to give you a summary of some research Dr Rob Davis and I did on the response of an urban reptile community to fire and which was published in PLOS ONE earlier this year: Rapid Recovery of an Urban Remnant Reptile Community following Summer Wildfire.

The study location

My home town is Perth in Western Australia, which is a sprawling city of 2 million people stretching ~125 km up the coast. The original eucalypt and banksia woodlands in this area supported a rich reptile assemblage of 69 terrestrial species.

Land clearing for urban development has turned most of the original vegetation into many small remnants and a few larger ones nested in between the suburbs. You can get an idea of this by opening up the map below in a new window, switching to satellite view and zooming out.

One of these larger remnants is Kings Park which is located just 1 km from the CBD and covers 4.06 km2, making it arguably the biggest inner city park in the world. The park is managed by the Botanic Gardens and Parks Authority (BGPA).

 

Being an urban remnant, Kings Park experiences a number of environmental pressures, with weeds and fire (mostly caused by arson) being amongst the most important. In January 2009, a wildfire burnt 40 ha of bushland at the park, which provided a great opportunity to study the immediate post-fire dynamics of the reptile community.

The study

Partnering with the BGPA, Rob set up 10 pitfall trapping grids following the fire: five each in burnt and unburnt areas. Each grid consisted of nine pitfall traps in a 3×3 grid, along with five funnel traps. Starting in November 2009, we surveyed these grids every spring and autumn for five years to track how the reptile community was affected and recovered post-fire.

A pitfall trap containing a young bearded dragon Pogona minor. Credit: J Krawiec.
A pitfall trap containing a young bearded dragon Pogona minor. Credit: J Krawiec.
Over 19,600 trap-nights, we captured 1,541 reptiles from 19 different species. This included:
  • 11 skinks
  • 2 legless lizards
  • 2 elapid snakes and
  • 1 species each of geckoes, dragons, goannas and blind snakes.

Species richness in spring (mean±SE: 6.12±0.29) was double that in autumn (2.98±0.23). We used the spring data to examine how the reptile community recovered over the course of the study.

Patterns of recovery

Species richness at unburnt sites (dashed green line below) was higher than that at burnt sites (solid orange line) for the first three years post-fire, with no difference between the two in the final two years.

Screen Shot 2015-09-22 at 3.07.35 pm

 

 

 

 

 

Total reptile abundance at unburnt sites was higher than at burnt sites in the first two years following the fire, but was similar between burnt and unburnt sites after that. Conversely, species evenness at burnt sites was higher than unburnt sites for the first two years.

Screen Shot 2015-09-22 at 3.07.42 pm

 

Interestingly, we also found that individuals of the skink Ctenotus fallens captured in unburnt areas were larger than those captured in burnt areas for the first four years of the study.

Screen Shot 2015-09-23 at 6.11.35 pm

Ctenotus fallens. Credit: J Krawiec
Ctenotus fallens. Credit: J Krawiec

Rare species are at risk

Although reptile abundance, richness and evenness at burnt sites had converged with that of unburnt sites by the end of the study, there were a number of species that showed a clear preference for unburnt habitat (72-100% of all captures occurring at unburnt sites).

This includes species such as Burton’s legless lizard Lialis burtonis and the southern blind snake Ramphotyphlops australis. Since the park is subject to frequent fire as a result of arson, there is a risk that the proportion of unburnt areas will decrease to the determinant of these species.

Blind snake Ramphotyphlops australis. Credit: J Krawiec
Blind snake Ramphotyphlops australis. Credit: J Krawiec
Burton's legless lizad Lialis burtonis. Credit: J Krawiec
Burton’s legless lizard Lialis burtonis. Credit: J Krawiec

What next?

The question then remains: how many years of post-fire recovery does it take for the habitat to become optimal for these species? Based on the data at hand, we can say that five years is not long enough.

By continuing our monitoring at Kings Park into the future, we hope to answer this question and others. Long-term monitoring will also enable us to assess how the reptiles respond to the warming and drying climate that south-western Australia is currently experiencing.

You can read and download the paper for free at this link.

Advertisements

2 thoughts on “Urban reptiles at risk from arsonists

  1. I’ve always wondered whether impact by “high residential density surrounding” a study area is somewhat unrecognized ? “Cryptoblepharus buchananii is a very common garden species in Perth, where it basks on walls and fences. Interestingly, despite its generalist nature, Valentine et al. [50] found this species to be more strongly associated with long unburnt areas in their study. This is in great contrast to our findings and may be more reflective of the higher residential density surrounding our study site (Valentine et al. [50] worked in a continuous wooded landscape), which may result in greater population sizes of this generalist and potentially disturbance tolerant species.”
    If our own species is regarded as apex predator, diurnal mesopredation may be reduced enabling rapid regeneration (of reptiles in this case).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s