The final opportunity to gathering data for
my MSc came to a quiet close on the 13th March 2013 after another week of
wandering about the thorny shrublands of Rooipoort Nature Reserve, Near
Kimberley. Although not successful in even the vaguest of definitions (well at
least not for my work), my field assistant, Paula, and I did make some
interesting observations and collected some DNA samples.
My study species, the Spotted sand lacertid
(Pedioplanis lineoocellata), was
incredibly scarce and we only sighted one definite individual- and a tiny one
at that, possibly less than 4cm long.
This was in contrast to the previous two
field excursions in which we found Pedioplanis
in abundance. In April 2012, a trip lasting 3 weeks, we captured, marked and
collected DNA from over 50 unique individual lizards, most of which were
apparently juveniles. The previous 3 week excursion in October 2012, saw us
capture over 60 unique individuals, all of which were adults. It appears- although without any
hypothesis testing to support this- that an early March field trip was
positioned awkwardly between the time the adults disappear and the juveniles
begin hatching. Although I haven't found any mention of an annual life cycle in
my study species (and I have seen at least two adult, gravid females active
during April), there has been suggestions that the sympatric Ichnotropis squamulosa is an annual of
sorts and does not live long after reproduction.
Interestingly, we caught six adult I. squamulosa in March 2013, only two
during the April trip but none during the October-November 2012 trip. This
could be an interesting case of temporal niche partitioning, the likes of which
are often demonstrated among plant species forced to share limited pollinators (eg. Stone, Willmer, & Rowe,
1998),
animals which would otherwise compete (Adams & Thibault, 2006) or sympatric lizards competing for the same food (Goldberg, 2008). Once again, these are just some 'itchy' ideas and by no means were
these observations enough to make such conclusions. This would make an
interesting study for an MSc student.
None of the above observations have
anything to do with my project.
My project was intended to examine the
relationship between real-time, actual movement of individuals within the
reserve to the gene flow inferred from genetic differentiation in
microsatellite loci. Researchers often use molecular markers to estimate gene
flow and in some cases dispersal because such markers are easy and straight
forward to collect, analyse and interpret whilst more direct measures of gene
flow and movement are laborious, expensive and often impractical or impossible
to perform. Although in common use, a simple inference of genetic distances to
estimate gene flow/dispersal has its pitfalls including some unrealistic
assumptions.
This project would aim to have a more
direct comparison of the relationship between genetic differentiation as an
estimate of gene flow (and indirectly, movement) to that measured from actual
movement.
The microsatellite analysis for my species
was fairly standard and included analysis like Least-Cost-Path analyses and Isolation-By-Distance.
The Capture-Mark-Recapture work, however, was less standard. When first caught,
lizards were marked with little number tags and a GPS co-ordinate was recorded
and a photograph of the lizard taken. A GPS co-ordinate and a photograph was
then taken every time the lizard was re-sighted.
The lizards were uniquely identified using the number
tags and the photographs through spot-identification software . These unique
individuals will be included in an analysis of movement based on the GPS
co-ordinates for each sighting.
When including a survey of local vegetation we can compare movement and
gene flow estimates across the reserve using estimates of 'resistance' that
each vegetation type may present.
Data collection in April was promising-
both from a genetics and CMR point of view but two days before my October trip,
we received news from reserve management that the site (and much of the rest of
the reserve) had burnt. As a result of this we had to move sites, and such are
the woes of a field biologist. Genetic sampling from the second site was decent
but the CMR data collected was a bit fishy. My suspicions were more because it
didn't seem to have the same pattern as that of the April dataset, that being
we had plenty of captures but next to no re-sightings. Whether this is because
we are comparing between different sites or between different age groups or
between pre- and post-fire is something I will have to ponder on when I finish
my analyses.
Every scientist is eagerly pounced upon by
the ‘average person’ with questions like “What is the point of this?” or “Why
put so much money into this?”, especially so when their study species is “…
some random lizard in the middle of no-where..”. We hope to gather very basic biologically and ecologically
relevant information without which any conservation planning for this species
would be unfounded. Science tries to tease out a straight forward relationship
from the inter-tangled mess that is real-world biology, so where people may
often think “Species A eats species B. The End.” It is far more
inter-connected. P. lineoocellata is
most probably a predator to many insects, a host to many parasites, a snack to
many bigger animals and may have some other ecologically relevant hobbies on
the side (what a busy guy!).
Above the basics for conservation, these
data will be used to improve the accuracy and reliability of Species Distribution
Models (SDM). Most SDMs have relied on correlations between species occurrence
and climatic data. This gives us an idea of what might happen to suitable
habitat under different environmental change scenarios but the assumption was
(and still is) often that said species can and will simply follow the suitable
habitat. This project allows us to incorporate mechanistic data (i.e. data
about the species and how it will respond biologically to change) into these
models. The application of
this is- you’ve probably guessed it- climate change predictions. If we are to
act pre-emptively as conservationist we need predictive power- What is likely
to happen in the future? And how will this detriment the survival of these
species? This predictive power comes
from activities such as SDM. These more intricate and skills-intensive work
give us the opportunity to plan ahead to develop mitigation plans for different
scenarios, brain storm possible social, financial and political barriers that
may prevent effective conservation and target the more sensitive or problem
species. This work on a seemingly
random lizard is expensive and very laborious but is necessary. Every step in
the process- from wandering
through the veld in 40°C heat, to making observation, collecting data,
analysing and interpreting the data and using it for a more applied purpose-
builds on our knowledge base and improves the effectiveness of our
conservation.
Ryan Daniels, SANBI, Cape Town
GDRI Work Package 4
References cited
Adams, R. a., & Thibault, K.
M. (2006). Temporal resource partitioning by bats at water holes. Journal of
Zoology, 270(3), 466–472. doi:10.1111/j.1469-7998.2006.00152.x
Goldberg, S. (2008).
Reproductive cycle of the common rough-scaled lizard, Ichnotropis squamulosa
(Squamata: Lacertidae) from southern Africa. Texas Journal of Science,
1–6. Retrieved from http://www.podarcis.eu/AS/Bibliografie/BIB_5453.pdf
