The first article that caught my eye was related to
pollination and its intrinsic link to plant biodiversity. Ecology and, more specifically, pollination
biology is one of my major interests, so it stuck out above most of the
genetics, biochemistry or microbiology articles that frequent many popular
science journals.
(Photograph taken in Nieuwoudtville, Northern Cape)
This article, authored by Anton Pauw from Stellenbosch
University is titled: “Can pollination niches facilitate plant coexistence”
(2013 Trends in Ecology and Evolution 28 (1): 30-37) and has the potential to
help us better understand the conservation requirements and ecology of the Cape
Floristic Region’s pollinators and plants, with potential implications for the
Western Cape’s eco-tourism and fruit cultivation.
Pauw is trying to find out why there are so many plant
species on Earth. This article,
therefore, focuses on an explanation for the origin of plant species and an
explanation for how they can coexist.
There are many ways plants can evolve and speciate [become a unique
species] and Pauw is looking specifically at the roles pollination and
pollinators play in it [Pollination: the transfer of pollen from the anther
(man-bits) to the stigma (lady-bits); Pollinator: an animal that carries the
pollen between flowers]. Changes in
pollinator are said to be associated with 25% of speciation events in plants
and is therefore responsible for a great amount of our plant diversity.
Pollinator-driven speciation creates species that are
different in their floral features. For
example, a change in the structure of a single-scent molecule in the nectar can
result in speciation if the different scent attracts a novel pollinator. The
broader question here is: “In the absence of other differences, are species
with different flowers able to coexist from an ecological perspective?”
The article revolves around Niche Theory, which says
coexistence is possible if intraspecific (within a species) competition is
stronger than interspecific (among species) competition. This expects that each species limits its own
abundance rather than be limited by the abundance of competing species.
Species generally limit their own abundance by using all of
a resource, and so the number of limiting resources determines the number of
species in a community of plants. If a
plant only has one specific pollinator, then it can become a limiting resource,
if the likelihood of a flower being pollinated decreases with increasing
density of flowers from the same species, which means it would produce less
seeds and have fewer offspring. This
scenario would allow for a mutant or alien invasive plant, which uses a
different pollinator (or pollinator resource) to invade the community and
coexist with the resident plants.
A good example of this could be in a monoculture (only one
species in the plant community) of a bird-pollinated species, the amount of seeds
the plants can produce may be limited by pollen transfer when there are lots of
flowers in the area if the birds become satiated and they do not visit every
flower, so some don’t get pollinated.
This monoculture could then be invaded by an insect pollinated species,
which won’t have this same limitation.
The two plant species can then have separate pollination niches.
Seven tests can be used to see if niche theory, driven by
pollinator speciation, is at play. The
article runs through these seven tests and the theoretical and practical
answers to them. From an exploration of
current literature and studies, it can be concluded that the jury is still out
on whether or not separation of pollinators can allow plant species to
coexist. Firstly, evidence is mounting
that the amount a flower or plant is pollinated declines with an increase in
the density of flowers from the same species.
Secondly, further evidence suggests that a decline in the amount a
flower is pollinated can decrease the growth of the total plant
population. Although no studies have yet
linked these two mechanisms to show that competition within the same species
for a pollinator can lead to the regulation and stabilisation of the density of
a plant population.
This study links neatly in with conservational issues. A deeper understanding of the roles of
pollinators in promoting plants species coexistence is required from a pure
academic perspective, but it can be crucial in showing the possible effects of
human influences (which is generally disruptive) on pollination and on the
diversity of pollinators.
If pollinators are, in fact, a limiting resource for plant
species, then a decline in their diversity can shrink the potential niche
space, most likely creating a domino-effect leading to decreased plant
diversity. The potential effects of this
are far-reaching and are not just trivial academic banter.
(Photograph taken on Table Mountain, Cape Town)
The Western Cape of South Africa contains one of the biodiversity
hotspots in the world, The Cape Floristic Region (CFR). It is the smallest of the six recognised
floral kingdoms and contains a disproportionately high amount of diversity and
endemism (meaning it occurs nowhere else on the planet). There are more than 9000 vascular plant
species of which 69% are endemic. So our
fynbos, which contributes to most of this diversity and endemism, is well worth
looking after. Not only is at extraordinary
floral marvel, but monetary worth of fynbos biodiversity, due to harvests of
fynbos products (e.g. wildflowers, honey) and eco-tourism is estimated to
around R77 million per year. So it is clear
that the CFR has both an economic and biological value.
The fair Cape that I live in is also a major producer of
fruit for the domestic and international market. The sheltered valleys between the mountains
are ideal for the cultivation of export quality fruits. This includes your apples, grapes (and our
delicious wine), olives, peaches and those juicy oranges. The disturbance caused by farmers and all
others to these regions has the potential do disrupt pollinator populations,
which could then have a negative feedback to our export quality fruits.
So by gaining a greater insight into the roles pollinators
play in plant species coexistence and their greater ecological role,
particularly in the Western Cape, it will allow us to lay down the theoretical
understanding that is necessary to implement the practical conservation in this
region.
