Alien invasive species are non-native species that have invaded a native ecosystem and settled and begun to thrive. Invasive alien species can take on any forms of life and may be microorganisms, fungi, plants, or animals. Invasive species are either intentionally or unintentionally introduced into a new ecosystem, habitat or country. As these species invade an already established ecosystem, they tend to have no natural enemies and flourish and spread within the ecosystem they have invaded. Alien invasive species have extremely negative impacts on the native species within the ecosystem that they have invaded. These impacts include the disruption of the ecology, hydrology and biochemical processes of the ecosystem, limiting and competing for natural resources.
The woody shrub you see before you is a prime example of an alien invasive species in South Africa, this shrub is known as Lantana camara L. (common names include lantana or shrub verbena). Originally from Mexico and Central America, and was introduced into South Africa from multiple places in the 1880’s and were distributed across the country as garden plants.
Lantana camara leaves and flowers, with immature berries in the background. Photo: NP Barker
An example of thrips (https://www.inaturalist.org/observations/184964396)
This alien invader has a profoundly negative effect on the environments and economies around the globe. It is a highly invasive species and leads to an overall decline in the diversity of the native species in that ecosystem, soil fertility, and ecosystem processes. Lantana also releases chemical compounds into the soil which prevents native plant species in close proximity from growing. The constant invasion of Lantana can result in a reduction of biodiversity within the ecosystem because it prevents succession and causes the displacement of native species.
Activity: Think of ways in which we can manage and remove lantana from our natural ecosystems.
Answer:
Discussion point: Many methods to remove aliens are also environmentally dangerous, so are they actually worth it?
Birds build nests to lay their eggs and raise their young. Nests can be built using many different techniques and materials, and therefore nests take on many different structures. A rather unassuming nest type would be the burrows you see before you in the sand bank. These are known as burrow nests. These specific burrows in the sand bank before you were made by Merops apiaster (European Bee-Eater) birds.
These nesting burrows were made by digging and removing the loose dirt in the sand bank. Nesting burrows can take on different forms and could be a simple shallow cave or a tunnel leading to a larger nesting chamber at the end which may be lined with nesting materials such as feathers and twigs. Birds may either build their nesting burrow or even take over holes suitable as a burrow from other birds or even mammals.
European bee-eater (photo: https://www.inaturalist.org/observations/73025344)
The European Bee-eater is a beautifully coloured bird with a yellow throat and back, black gorget, chestnut back, and turquoise chest and belly. European Bee-eaters prey on flying insects and hunt them down whilst in flight. These Bee-eaters particularly enjoy feeding on bees, wasps and flying ants. Once the insect has been caught, these birds will land on a perch and repeatedly bash the insect against the perch to kill it, cleverly removing its sting before gobbling it down. They are migratory birds and will travel extremely long distances to Eastern Europe during our winter, and then travel back for summer, arriving around October. The European Bee-eater is a social bird that breeds in large colonies. They build their nests by tunnelling into riverbanks or sandbanks and create a nesting chamber at the end of the burrows tunnel. These birds are monogamous and both the male and female will sit on the eggs until they hatch.
Activity: Nests generally serve the same purpose: to protect the eggs until they hatch and to protect the baby birds until they reach maturity. However, what do you think are the various ways in which different kinds of nests protect the eggs and baby birds?
Masked Weaver nest. Photo:https://www.inaturalist.org/observations/186724685
Pigeon nest. Photo: NP Barker
Blacksmith Plover nest. Photo: NP Barker
Wire-tailed Swallow. Photo: https://www.inaturalist.org/observations/176300802
Answer:
The hidden world under your feet!
You are standing on the ground – unless it’s an urbane area this is likely to be soil. Soil is very important, and usually has a specific structure called the soil profile. A soil profile consists of layers called soil horizons. As you can see in the sand bank before you, there is a very clear soil profile with very clear soil horizons. Within this soil profile, roots can also be seen reaching down into the deeper layers of the soil. Plant roots grow down into the soil through holes and cracks. At the tips of growing roots, very fine hairs are produced that are used by the plant to absorb water and nutrients.
Diagram of soil layers (source: https://www.freepik.com/premium-vector/soil-structure-layers-ground-cross-section-education-diagram-grass-humus-topsoil-subsoil-parent-rock-bedrock-geology-vector-banner_23630617.htm)
Diagram of plant root and root hair growing in soil (source: https://www.aplustopper.com/absorption-roots-icse-solutions-class-10-biology/)
Soil consists of particles of minerals (sand, silt and clay), organic matter, air, water and…living organisms. All of these contents constantly interact with one another.
However, there is much more than meets the eye when it comes to soil! Within soil there exists a microscopic ecosystem known as the soil microbiome. A soil microbiome refers to the community of soil microbes living within soil. Soil microbes are microscopic organisms that live in the soil and perform various tasks to maintain soil fertility. These microscopic organisms can be classified as fungi, bacteria, archaea, protozoa, or viruses. Soil microbes play roles in breaking down organic matter, transforming nutrients into forms in which plants can easily access, control and limit the number of disease-causing microorganisms, and aid in humus production. Soil microbes are tiny but mighty, and are necessary for forming soil and sustaining life. Various farming practices such as ploughing can disrupt the microbiomes of the soil by disrupting the populations and activities of the soil microbes.
Activity: Other than being the substance in which plants grow and housing microorganisms, what other functions does soil serve?
Can you see the different layers of the soil profile, and can you name them when compared to the diagram below?
Answer:
You are currently standing on part of the Magaliesberg mountain range. Did you know that this mountain is nearly 100 times older than Mount Everest? It is! Formed more than 2 billion years ago, these mountains are one of the oldest mountain ranges on the earth! The mountain range stretches from near the Bronkhorstspruit Dam through 120 km to Rustenburg. Along all this distance, the geology changes and gives rise to a variety of different habitats including grasslands, bushveld savannah and inaccessible forested kloofs. Altogether, these different habitats hold a great diversity of organisms, including over 130 different types of trees, a huge variety of flowers, ferns, grasses and fungi.
These lands, although beautiful, have a rich and turbulent history. Earliest knowledge tells us that these mountains were once home to the Batswana people, before they were invaded by the Ndebele tribe. This invasion was led by the formidable King Mzilikazi, who then took charge of the land and the people from the Vaal River up into Limpopo for the next 10 years. In this time, the land was visited by European early adventurers, who had heard about the famous Mzilikazi and the wildlife in these areas. Soon after, Dutch voortrekkers, coming from the British ruled Cape, ventured into these lands and drove out the Ndebele people. They founded their own settlement and renamed the mountains the Magaliesberg, named after Chief Mogale, who fought against Mszikilazi. Mogale later hid from Mzilikazi in these mountains, until the 1830’s when the voortrekkers drove Mzilikazi out of what was then the Transvaal. These mountains then saw several more wars, notably between the Dutch and the British, namely the Transvaal War (1880-1881), the South African war (1889-1902) and the 1914 Rebellion. Part of the Magaliesberg was proclaimed a World Biosphere Reserve in June of 2015 by UNESCO. However, the part where you are standing is excluded from this reserve.
Discussion point: Think about and discuss what you can do to try and conserve this part of your natural and cultural heritage.
An aerial view of the Magaliesberg and Hartebeestpoort Dam, looking westwards. Photo: https://ilovesouthafrica.com/gauteng/visit-magaliesburg/
Peaceful stream pool somewhere in the Magaliesberg Mountains. Photo : https://yourneighbourhood.co.za/mountain-sanctuary-park-in-the-magaliesberg-mountains/
The landscape and scenery of these mountains you are standing in comprises a vegetation called Savanna – more specifically the Savanna Biome. A biome is a region defined by both the plants and other life forms as well as the climate. There are nine biomes in South Africa.
Covering approximately 46% of southern Africa, and more than a third of South Africa’s land mass, the Savanna biome has a ground layer that is filled with grasses and a sparse upper layer consisting of woody shrubs and trees. It is well developed over the lowveld and the Kalahari regions of South Africa, as well as in Botswana, Namibia and Zimbabwe.
Map of the savanna biome. Source : https://pza.sanbi.org/vegetation/savanna-biome
Typical savanna scene Source: https://www.conserve-energy-future.com/savanna-biome.php
Savanna fire in the Waterberg, near Vaalwater. Photo: NP Barker
Weather patterns in this biome are complex. The rainfall varies between 235 and 1000mm per year, which comes during the summer months. This rainfall is not sufficient to support the upper layer of plants, meaning that trees do not dominate these landscapes. The summer rainfall is essential for the grass dominance. In the dry season, the grasses dry out, which provides fuel for annual fires. For this reason, almost all of the plants in these areas are adapted to fire survival. There are several different fire survival strategies that plants use. Some plants have extensive underground parts so that when the top parts are burnt, they can simply resprout. Other plants may have outer bark or leaves that actually protect the inner parts of the plant from fires. This means that, after a fire, the plants are either able to resprout from the stem, or from seed, or will simply still be standing after the fire.
Fire is usually thought of as something that is destructive, but in these environments, it can be quite beneficial. Although it does kill a lot of the vegetation (which is often able to regrow because they have adapted to fires) and can kill beneficial animals, fires also cleanse the lands of problematic pests and invading species. Additionally, as the soil is heated briefly by the fire’s heat, certain seeds are actually cracked open and can then germinate. The ash that results from the fire is also beneficial to the soil composition, and therefore benefits the plants that germinate and those that resprout.
Savanna is used for grazing, mainly cattle or game, and many of our wilderness and game park areas are found in this biome, including the Kruger and Kalahari Gemsbok National Parks.
Activity: Can you see evidence of previous fires that have happened here? What is this evidence? Have any plants been killed by the fire?
Answer: Look for charcoal marks and blackened bark and branches, or blackened stumps of plants.
We all know the purpose of seeds – they grow into new plants (i.e. plant reproduction). But did you know that seeds can travel great distances from the plant that made them? This is called seed dispersal. Seed dispersal is the method by which seeds are spread throughout the lands, and the reason why plants are found all over the planet. One might ask, why is it important for seeds to be able to be spread, why not have a cluster of plants all near to one another? The answer is simple. When seeds are able to grow far from the parent plant, the baby plants have a higher chance of survival, because they are less likely to compete for space, water, nutrients and sunlight.
There are various ways that seeds can end up far away from the parent plant, but the common methods of seed dispersal are wind, animal and to a lesser extent water.
Animal dispersal: Seed can be spread by animals, which either eat them and then pass them out together with nutritious dung.
Seedling growing out of Elephant Dung. Source: https://www.scienceabc.com/nature/animals/what-role-do-elephants-play-in-ecosystems.html
In the area nearby, there are trees of the Monkey Orange (Strychnos spinosa). Look for a 5-8m high tree that has pale grey bark with patches, leather green leaves which have a minute spine on the tips. The fruits are bigger than a tennis ball, and are green but ripen to a orange -yellow. Inside the fruit there are tightly packed seeds surrounded by edible flesh. These fruits are eaten by monkeys, baboons, bushpigs, nyala and eland, as well as us humans!
Strychnos pungens on Mamelodi ridge. & Fruit of the Monkey Orange (Strychnos spinosa), found in this vicinity. Souce: https://www.inaturalist.org/observations/171214616
Alternatively, seeds can stick to the outside of an animal’s fur or birds’ feet or feathers. Seeds that are adapted to being dispersed in this way often have small hooks, like the annoying blackjack seed!
Fruit head and inflorescence of Black Jack (Bidens pilosa). Note the hooks that attach to animals. Source: https://commons.wikimedia.org/wiki/File:Bidens_pilosa_100227-0076_tdp.jpg
Some grass seeds have a long twisted structure called an awn that twists and tangles in animal fur. There is a lot of this grass in patches in this area. Can you see the seeds knotted together? Take one and wet the awn in your mouth and watch – it will start twisting in your fingers.
Look for these twisted heads of grass seeds This is a grass called Tanglehead (Heteropogon contortus). Source: https://www.inaturalist.org/observations/148094770
Wind dispersal: Seeds that are spread by wind are light and will often either have hairy parts to them, or will have something like a wing (or few), both of which help them float on the wind. There are several plants in this area that have wind-adapted seeds / fruit. Look out for them!
The winged seeds of Combretum zeyheri (Large fruit bushwillow), a typical savanna tree. Source: https://www.inaturalist.org/observations/55251921
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