Pioneer Species

Pioneer species

The first organisms appearing in the regions of primary succession are pioneer species (usually lichens or mosses). They are the first species present. They must be strong and hardy.

The development of a new community is succession. The sequence of types of vegetation taking place at the time of succession is referred to as sere. Primary succession is the formation of a new community where the environment is devoid of life. The first groups of entities that are established are referred to as pioneers.

Primary succession takes place in regions that were never inhabited by a community. Primary communities help in enriching soil. As and when the generations of lichens or mosses die, its remains decompose and get added to the soil. Then, the soil can provide for a diverse plant life.

What are Pioneer Species? Definition of Pioneer Species

Pioneer species are hardy species. As the name suggests, they are the first ones who are known to colonise barren surroundings or formerly biodiverse steady-state ecosystems, which are disrupted (for instance by fire).

“Pioneer species are entities which are particularly adapted to colonise the lifeless, barren regions and start an ecological community”.

Habitat and Reproduction in Pioneer species

Such entities alter their surroundings as they inhabit, survive and produce conditions for other entities to come there and start a livelihood in the area. Consequently, it has an effect on other entities. Some of these changes could be a change in the abiotic state such as in the temperature, soil etc. along with changes in the biotic state.

There are some lichens growing on the rocks in the absence of soil, hence can be from the first of the life forms, breaking down the rocks into the soil for plants. As a few uncolonised lands can have fine and deterred quality soil having little to no nutrients, the pioneer species usually are hardy plants having adaptations namely long roots, root nodules having nitrogen-fixing bacteria and leaves which exhibit transpiration.

Usually, they are photosynthetic plants, since no other energy source (exception being light energy) is generally available in the beginning phases of succession. Consequently, the likelihood for pioneer species to be non-photosynthetic is less. Often, the plants that are pioneer species have the tendency to be wind-pollinated instead of being pollinated by insects, as it is less likely for insects to be seen in the barren environment where the pioneer species inhabit. Having said that, the pioneer species broadly have the tendency to indulge in asexual reproduction due to the existence of barren or extreme conditions causing asexual reproduction to be more favourable to no increase reproductive success instead of investing energy in sexual reproduction.

These species can die producing plant litter, breaking down as the “leaf mold” in a while, which makes new soil for secondary succession and nutrients for small fish and aquatic plants in the nearby water bodies.

Pioneer Species Characteristics

Some of the features of pioneer species that enables it to live in regions that are extreme for other forms of life are:

Hardy

These species can withstand and live through any type of existing extreme environmental circumstances.

Nature

Pioneer species are of the nature of exploring new habitats. They must be agile entities and must possess a great potential to adapt to new surroundings. Such species are good breeders, have a wide choice of food and are tolerant species.

Light-induced Seed Germination

In nature, generally, the seeds of the pioneer species are photoblastic. It germinates by the trigger of light and they are strong light-demanders. Since in normal conditions, a seed germinates under the provision of optimal conditions, the seeds of pioneer species do not have much demand provided the conditions they inhabit. The only requirement to germinate is said to be “light-stimulation”.

Seeds are Easy to Germinate

These species have seeds with a net moisture content of less than 5% and are still viable enough to show great longevity. This feature helps them to propagate even after a long time after dormancy. With ease, they can withstand desiccation and produce new plants after the stage of germination.

Short Life Cycle

As extreme conditions such as barren lands offer very few options for species to persist, pioneer species have emerged to exhibit a short life cycle, which is indicative of an early reproductive phase. Reproductive maturity tends to occur quickly in these species, be it an asexual or sexual mode of reproduction.

Role of Wind in Pollination

Since conditions are extreme for species in barren lands, wind pollination is the only action for probable pollination. In almost all sexually reproducing pioneer species for whom pollination is critical for gamete-fertilization, wind pollination is the mode. Also, the process of seed dispersal is through the wind.

High Rate of Seed Dispersal and Production

Pioneer species’ seeds are extremely viable and are produced in a geometric manner, showing great dispersal rates. To colonise land that lacks nutrients, it is compulsory to have this dispersal rate.

Size of Propagule is Small

The small size of it helps in easy dispersal and recognition of succession goals. In addition, the small seeds raise the chances of germination, as they can get stuck in tiny holes and cervices at the time of hostile phases.

Asexual Mode of Reproduction is More Favourable

As the sexual mode of reproduction demands more energy and consumes time, pioneer species may not be best suited for it. There are cases, however, wherein pioneer species take part in sexual reproduction. The asexual mode, however, is more widespread as a result of its numerous benefits.

Pioneer Species Examples

Some examples of pioneer species are as follows –

• Pioneer fauna – snails, worms, some toads etc
• A pioneer species of lyme grass (Leymus arenarius) on a barren land of sand
• Species of plants that inhabited a newly formed region from a solidified lava flow (Polystichum munitum, swordfern, moss Racomitrium ericoides)
• Cyanobacteria – Anabaena, Rhizobium
• Bryophytes – Hyophila involuta
• Lichens – Placopsis gelada
• Bacteria – Thiobacillus spp.
• Angiosperms – Lupinus lepidus

Pioneer Species In Ecological Succession

Ecological systems involve biological interactions between different components of the natural systems and their interrelations. Their interactions and associations decide how the ecological system will operate, their sustainability, the necessities and rate of survival and other related aspects. Ecological communities are area-specific and are based on how the species which are “common” are in harmony.

Ecological succession includes all the processes, factors and interrelationships in a community that governs its evolution, spanning across a timeframe. It includes the structural behaviour and changes of a biological community over the evolutionary period.

Succession

Several processes set up animal or plant communities in an ecosystem. When enough sources of food exist, a new population can thrive in that ecosystem. The process wherein communities get set up, change and develop in ecosystems is referred to as succession.

Types of Succession

• Primary succession
• Secondary succession

When the pioneer species start the ecological succession in a region that was barren earlier, it is referred to as primary succession. If the succession begins in a region where existing life has been destroyed, then it is referred to as secondary succession.

Pioneer Species in Primary Succession

Primary succession starts in the barren regions, namely bare rocks which are disclosed by a retreating glacier. Here, the first ones to inhabit it are plants or lichens. These are those which can tolerate and thrive in such conditions. Over centuries, such “species” transform rocks into the soil which can provide for simple plants (grasses).

Further, such grass alters the soil, after which it is colonised by other kinds of plants. At every successive phase, there is a modification in the habitat which changes the quantity of shade and the soil composition. The climax community is the final phase of succession that is an extremely stable phase that can sustain for years together.

Primary Succession Examples

Simple entities which could withstand extreme environmental conditions were first established. Often, the first entities to appear in the regions of the primary succession are lichens or mosses and are referred to as pioneer species as they are the first species found. Like human pioneers, the pioneer species are required to be strong and hard. Some of the places where primary succession takes place are the newly exposed rock regions, lava flows and sand dunes. A class of algae – cyanobacteria/blue-green algae and only plants are taken into account as photo-auto-lithotrophs.

Pioneer Species in Secondary Succession

Secondary succession takes place in areas that are disturbed, which could either be due to man-made or natural causes. Secondary succession can take place in cutover forests, crop fields, regions destroyed by floods or wind storms and other formerly occupied areas. The circumstances that lead to secondary succession are typically hard.

For instance, if an area was used for agricultural purposes for years, the quality of soil could get deterred or devoid of vital nutrients.

When there is secondary succession, typically the communities are reintroduced to the ecosystem at a faster pace compared to primary succession.

The animal and plant communities that existed before the disturbance already result in secondary succession. Hence, the soil is richer often in regions wherein primary succession takes place. Additionally, some species can stay in the areas even after a disturbance. For instance, plant species like weeds can still survive in a disturbed area and are quick enough to establish themselves. Seeds or cones can stay on the ground or in the soil. If the condition of the soil is right after a disturbance, the seeds and cones can germinate and commence a new plant community.

An important point to note is that the species in the secondary succession do not essentially have to be photo-auto-litho-trophic.

Secondary Succession Examples

Secondary succession takes place in regions wherein some of the nutrient sources already exist in the substrate. The areas such as deforested areas, forests that are logged, regions that are influenced by windstorms and so on are faced with secondary succession. Some other examples of pioneer species causing secondary succession are tree species such as Betula spp., microbial species (archaea, bacteria), Alnus spp. etc.

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