Download - Botanical Society of South Africa

learning about biodiversity Ecosytems
“An ordinary desert supports a much greater variety
of plants than does either a forest or a prairie. “
Ellsworth Huntington
In the new Life Sciences curriculum for Grade 10:
STRAND: Environmental Studies
Grade 10: Biosphere to ecosystems
Organisms interact with other organisms and with the environments in which they live in order to survive
and produce offspring. The study of these interactions is called ecology. This section is structured so as
to expose students to some of the interactions that occur in nature and to the terminology and concepts
that describe them. The terminology and concepts selected here (LO 2) will be used in Grade 11 and
Grade 12 across all strands, where appropriate. It also enables students to contextualize the meaning of
these terms and concepts within the familiar contexts of both southern Africa (LO 2) and their local area
(LO 1). The use of a local area context is also used to introduce human influences on the environments
in which they and other organisms live (LO 3), a thread which will be expanded on both within local and
global contexts, in more detail, in Grade 11.
LO1 Investigating phenomena
in the Life Sciences
LO2 Constructing Life
Sciences knowledge
LO3 Applying Life
Sciences in society
Biosphere to ecosystems
Choose an ecosystem within
a local biome for special study
Identify the abiotic and
biotic factors operating and
describe the interactions
between them
Explain the trophic
relationships present
If possible, record and
describe seasonal changes
Use keys and field guides
to learn about biodiversity
within the biome
An excellent guide
book to introduce your
Grade 10 class to the
concept of identifying
plants is What’s that Tree: A starter’s
guide to trees of southern Africa by
Eugene Moll. It identifies all the
families of trees and shrubs with
great photos and easy to remember
common names. See page 46 for
details of the book.
Biosphere
Concept of the biosphere. Interconnectedness of components of
global ecosystems
Biomes
Terrestrial and aquatic biomes of
southern Africa: describe in terms of
climate, soils and vegetation
Ecosystems
Theoretical understanding of
ecosystems
Abiotic and biotic factors: effects on
community structure and ecosystem
function
Energy flow through ecosystems and
relationship to trophic structure
• Trophic levels: producers,
consumers (herbivores and
carnivores), decomposers
• Food chains, food webs and food
pyramid
Nutrient cycles: water, oxygen, carbon
and nitrogen
[Names e.g. nitrates are required but no
detail of chemistry is necessary]
Choose at least ONE
example of human
influence within the
ecosystem chosen for
study in LO 1
Describe the selected
human influence
and the reasons for
it having a positive
and/or a negative
impact on the
ecosystem
[This serves as an
introduction/link to
human influences on
the environment in
Grade 11]
Ecotourism:
economics, ethics
and opportunities
A Succulent subject
In the table opposite you will see what is
required learning for part of the Life Sciences
curriculum for Grade 10. The poster overleaf
will assist in the teaching of ecosystems as
it demonstrates how our indigenous succulent
plants have adapted to the biotic and abiotic
factors in their environment. In fact our
Succulent Karoo Biome is one of the world’s
twenty-five ‘hotspots’ – geographical areas
which contain the world’s greatest plant and
animal diversity, with associated potential for
ecotourism. The fascinating plants that occur
in these arid area ecosystems could not fail to
interest all learners.
Succulents are the easiest plants to grow,
either in your school garden or to use for basic
class experiments, for example, on how
plants react to light (see p. 27).
Succulents are also useful in schemes to store
carbon in attempts to remove CO2 from the air to
help slow down climate change. (See ‘Investing
in sustainability’ by Amanda Bourne in the
December 2010 Veld & Flora, p. 153.)
Human interest
The plant below is a Ghaap (Hoodia gordonii),
a spiny succulent that grows in the semi-arid
areas of southern Africa. The young growing
tips of the plant have been eaten by humans for
centuries to quench thirst and suppress hunger.
Today it is used commercially as part of a diet
preparation to curb obesity.
Link the nutrient
cycles to current
environmental issues,
e.g. the threat of global
warming and how it is
affecting the Earth
Shaping up
ABOVE: The Candelabra Flower (Brunsvigia radulosa) from the Drakensberg.
Photo: Clinton Carbutt.
The flagship article on p. 10 of this issue of Veld & Flora, ‘From crags to riches’,
illustrates the concepts outlined above very well. The Drakensberg Alpine
Centre is the only centre of plant endemism in southern Africa characterized by
a sub-alpine and alpine environment, and it is estimated that its total flora (i.e.
from mosses to trees) is 3 000 native species, which means it contributes one
in ten species to the flora of southern Africa – a flora renowned as the most
species-rich temperate flora in the world! The author explores the question of
why the flora of the Drakensberg Alpine Centre is so diverse and in doing so
explains the historical factors that may have shaped the distribution of this flora
(plant geography) as well as the more localized interactions between this flora
and its environment (plant ecology). Several other articles in this issue, notably
‘The lost fynbos of Tokai Park’ on p. 30 and ‘Drawing a line in the sand’ on p. 34,
are also about the importance of functioning ecosystems.
MARCH 2012
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learning about biodiversity
Liliput and Goliath:
Coping wit
Temperature
Why are so many of the dwarf succulents confined to the winter
rainfall areas and the arborescent (tree-like) species to the
eastern and northern parts of South Africa? Here climate
dictates: a short, cool, moist winter with long, dry,
hot summers often results in dwarfism, whilst warm,
subtropical, moist summers encourage plants to grow
gigantic. Low temperatures during winter demand a
dwarf growth, close to the ground, where they can make
use of the warmth of the soil. During summers they go
into their resting phase. The dwarf mesembs such as
Conophytum, recycle their moisture from the old leaf pair
to the younger leaf pair while retaining the old, dry leaf pair
as a protective covering for the young leaves. Their highly
advanced local seed dispersal ensures they remain within their
habitat which is often on quartz gravel hills.
At the other extreme, high temperatures often result in large barrelshaped succulent stemmed plants, such as the Bottle Tree (Pachypodium lealii), Baobab (Adansonia)
and many of the taller Euphorbia species. Growth is cylindrical and tall, getting away from the very
hot ground. The Richtersveld with its winter rainfall, covers a much smaller area (almost four times
smaller) than the Kaokoveld of Namibia with its subtropical summer rain, but the latter is much
poorer in species. Dwarfism allows for specialist adaptation, and the Land of Liliput can thus fit in
many more species than the giants in the Land of Goliath. The dwarf succulents are very popular in
succulent collections as they take up less space, and many of them can be grown indoors.
Succulent plant diversity in South Afri
rich and fascinating. Spanning man
miniature tufted plants such as Cono
the world’s largest succulent. Suc
evolutionarily advanced in compariso
Let’s explore some of the ways they
An ecosystem is made up of
living organisms that interact
with each other and their
environment. The biotic
components are the living
organisms such as plants,
animals and micro-organisms.
Ingenious ways of storing
moisture:
Water
Why are succulent’s leaves and stems often cylindrical or
round in shape? This is the best surface to volume water
storage ratio! We make use of water tanks which are
cylindrical in shape for storing water. Apart from succulence many have features for coping with seasonally dry
conditions. Botterboom (Tylecodon) forsake their leaves for
the long dry summers, relying on their green photosyntheticactive succulent stems. Kobas (Cyphostemma) illustrated in
the centre of this poster, follows the same strategy but loses its
leaves during the winter. (A good example of convergence – where
two different plants from different families follow a similar strategy.)
Most mesembs have terete leaves (cylindrical or slightly tapering, without
ridges) orientated towards the sun, thus avoiding the full blast of the sun’s rays.
All plants transpire to keep cool through their small breathing pores (stomata). How do
succulents avoid too much water loss which could result in desiccation? Some succulents have a
grey or whitish colour which reflects sunlight, others have a dense, whitish, hairy skin (epidermis)
such as Senecio haworthii. The Giant Iceplant (Mesembryanthemum barklyi) illustrated on the left
is covered with reflective glittering bladder cells.
Read more
Discover more
about succulents
in these articles
in back issues of
Veld & Flora.
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VELD&FLORA | MARCH 2012
Charting uncertainty: Global climate
change and its implications for our flora
by Guy Midgley et al, vol. 88(2) June 2002
on page 70.
Cliff hangers: What defines a cliff
dwelling succulent plant? by Ernst van
Putting down ro
Succulents can grow in shallow s
little competition from other plan
when the top layer of the soil d
their succulent nature which allo
falls, can. In the Karoo with its lo
deep roots which draw up moi
alongside them with their shallo
nature. Many succulents grow in
enable them to cope with t
Jaarsveld, vol. 88(4) Dec. 2002 on page 154.
Desert grapes: An epeditition to the remote
reaches of the southern Namib by Ernst van
Jaarsveld, vol. 94(2) June 2008 on p. 82.
Fanfare in the fynbos: Aloe plicatilis, a
unique Western Cape tree aloe by Stephen
Veld & Flora FACTSHEET SUCCULENTS
th adversity
ica’s low rainfall regions is exceptionally
ny different families, they vary from
ophytum to the big and bold Baobab,
cculents are highly specialized and
on to plants from high rainfall regions.
cope in their low rainfall ecosystems.
Abiotic components of an
ecosystem are the nonliving
components
that
affect plants and animals.
They include temperature,
water, light and soil as well as
altitude and aspect.
oots:
Red and green:
Light
Like all green plants succulents have to trap carbon from
the atmosphere for their normal food production and
growth. Many succulents turn a reddish colour during
dry conditions. This is the result of a pigment, anthocyanin, which is the plant’s solution to slowing down
photosynthesis and thus ‘dimming’ the sun’s bright
rays. Succulents thus put their foot on the brakes
when moisture becomes scarce. This reddish colour
is not confined to succulents, and you can often see it
in young leaves (for protecting the young, vulnerable
tissue) or in deciduous trees and fruit which ripens (a
sign that the fruits are ripe).
Many succulents keep their breathing pores closed during
dry, sunny conditions, only opening them during the night. How
do they manage to photosynthesize, which requires CO2? During the
night, the plants accumulate organic acids to which carbon is bound, which during the day, are
broken down again and the CO2 released making it available without having to loose moisture via
their breathing pores. This is known as Crassulacean Acid Metabolism (CAM).
Not all succulents grow in full sun. Most of the smaller species grow on south-facing slopes or
below Karoo shrubs that provide protection from the sun.
Avoiding predation:
ABOVE:
Xing
Quan from
the Beijing
University
Botanical
Gardens up a Kobas
(Cyphostemma currorii)
growing in Omavanda in Namibia.
Soil
soils, even on bedrock, where there is
nts. Most plants simply cannot survive
dries out but succulents, by virtue of
ows them to survive until the next rain
ow rainfall, many of the shrubs have
isture, whilst the succulents survive
ow roots and fleshy, moisture storing
clayey soil too, as their shallow roots
the low oxygen content of clay.
Animals
The high water content of succulent plants makes them vulnerable
to herbivores, particularly the larger mammals. There are various
ways they avoid predation. The big and bold succulent plants
such as Aloe ferox and most euphorbias are spiny, and any
animal would think twice before taking them on. They also
have another trick up their sleeve – chemicals. Aloes are
extremely bitter, and euphorbias have a with milky latex
that can damage eyes or burn skin.
Another clever strategy some follow is to blend in with
their background (camouflage). This group is usually small
and humble; some resemble stones (stone plants such as
Lithops and Pleiospilos), others simply have mottled green
leaves (Gasteria and Senecio articulatus) which grow below
shrubs and are thus difficult to see. There is also a large group of
dwarf succulents that rely on other plants for their defence. They hide
below spiny shrubs (nurse plants) and are thus well adapted to grow in shade
which is why they make such good indoor plants.
Some, like the large and very palatable Spekboom (Portulacaria afra) however, are quite without any
defence. They make use of a different strategy altogether – passive resistance! Any bit of vegetative
material that falls to the ground when broken off the parent plant, immediately roots and forms a new
plant. Karkei (Crassula ovata), Klein-karkai (C. tetragona), Ox-tongue (Gasteria), Adromischus and many
others have also evolved this strategy, turning predation into procreation.
Cousins, vol. 96(4) Dec. 2010 on p. 164.
Fog and dew in the Succulent Karoo: An
indispensible source of water for arid
Succulent Karoo shrubs by Ignatious
Matimati et al, vol. 96(3) Sept. 2010 on p. 140.
Kleinduimpie Grass: the only succulent
grass in the world by Ernst van Jaarsveld, vol.
95(1) March 2009 on page 19.
The quarzite ridges of Gauteng by Michèle
Pfab, vol. 88(2) June 2002 on p. 56.
The remarkable Kaoko Klipblom by Ernst
van Jaarsveld, vol. 93(1) March 2007 on p. 42.
Text and photographs
by Ernst van Jaarsveld
and Caroline Voget.
Download these articles
at http://LABpages.
blogspot.com.
MARCH 2012
| VELD&FLORA
25
learning about biodiversity
How we lost the African acacias
The science of classifying plants (or indeed, any living organism)
is called taxonomy. Taxonomists the world over follow a method
invented by Linnaeus by which he organized plants into a hierarchy
of increasingly specific groups from the Kingdom down to the
smallest group, the species. He based his classification on external
characteristics, like similarities of structure. This means that all living
things have a scientific place and name that anyone in the world
would recognize. Our Sweet Thorn is Acacia karroo, even though
it has numerous common names – Sweet Thorn, Soetdoring,
Mookana, Mooka, umuNga and so on. Scientists studying it would
know it as Acacia karroo and in that way they can track any studies
that have been published about it in the scientific literature
anywhere in the world.
The many species that share the genus Acacia, in turn are grouped
into the Thorn Tree or Mimosa subfamily (Mimosoideae), which
belong in the Legume family (Fabaceae), which ultimately is placed
in the Kingdom of Plants (Plantae). (The genus and the species is
always written in italics, the genus capitalized and the species in
lower case.)
Up till now, based on several external features like feathery leaves,
stipular scars or spines, or the presence of pods, botanists recognized
about 1350 Acacia species in Africa, tropical Asia, Australia and in
the tropical Americas, including some 40 species of African acacias
(the thorn trees) and almost 1000 species of Australian acacias (the
wattles). The latest taxonomic studies however show that the genus
needs to be broken down into five genera, but what to do about
naming the new genera?
What should have happened
The International Code of Botanical Nomenclature (ICBN), which
was established to maintain order in the world of taxonomy,
adheres to certain rules and regulations for naming and classifying
plants. When researchers show that a genus needs to be split as in
the case of Acacia, the generic name is kept for the plants that are
the same as the ‘type species’ (which is the actual plant on which
the original species description is based). In this case there is some
confusion as the type species for Acacia is Acacia scorpioides, which
for some reason is no longer an accepted species, and is instead a
synonym of the Scented Pod-thorn (Acacia nilotica). Nevertheless,
if Acacia was to be split, and if the genera were named in accordance
with the original type species, the name Acacia should have gone
with A. nilotica to the 161 species in Africa, Asia, the Americas
and a handful in northern Australia. Almost all of the Australian
species would have needed new names under the next oldest
RIGHT: The Sweet Thorn (Acacia karroo).
Painting by Helga Streicher.
BELOW: A giraffe under an Umbrella Thorn
(Acacia tortilis).
available generic name which
was Racosperma.
But what actually happened
The ICBN makes allowances
for special cases to be referred
to relevant committees of
the International Association
for Plant Taxonomy (IAPT) for
a legislated exception if the
strict application of the rules
of nomenclature would cause
unnecessary disruption, and this is what a group of Australian
botanists did. A case was put forward to change the type species
of Acacia in such a way that, were the genus to be split up, the
generic name Acacia would follow the largest group: the 1000odd wattles. In mid-2004 it was announced that the committee
had made a decision to allow a new Australian type species,
Acacia penninervis. This meant that the wattles would keep the
name Acacia and the African thorn trees would have to change.
To the collective dismay of African botanists, this was endorsed
by the General Committee of IAPT and ratified at the International
Botanical Congress in Vienna in 2005. At the next International
Botanical Congress in Melbourne in 2011 there was a valiant
attempt to challenge the process and outcome of the decision,
but unfortunately it was not successful.
So now, when the genus is finally split, the name Acacia will
still apply to the 948 species of Australian wattles, seven related
species in the Pacific Islands, one or two in the Madagascar region
and 10 in tropical Asia. A few northern Australian species will have
to change their generic name to Vachellia, and two will become
Senegalia. The pantropical (tropical Africa, Asia and America)
acacias on the other hand, will all become Vachellia, including
Acacia karroo and Acacia tortilis, or Senegalia.
The future of our acacias
Can African scientists just ignore this unfair hijacking of our
iconic African thorn trees and carry on calling our acacias Acacia?
Sadly, it is not really an option as any scientists wanting their
work published in internationally recognized journals would
have to adhere to the internationally accepted scientific name.
So, it seems, the iconic African name, acacia, will live on only as a
common name.
Linking to the Curriculum In Life Sciences, for Grade
10, this article links in with the strand ‘Diversity, change &
continuity: History of life and biodiversity’, the underlying
concept to be taught being that ‘Life exists in a huge array of
forms and modes of life at present, which scientists organize
according to a man-made classification system.’
In Grade 11 it links to the strand ‘Diversity, change and
continuity: Diversity of animals and plants and biogeography’
the underlying concept to be taught being that ‘Plants and
animals can be grouped according to similarities in their basic
structure or body plan.’
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VELD&FLORA | MARCH 2012