Hydrological niche segregation

Mountain Fynbos

Fynbos is a natural shrubland or heathland vegetation occurring in a small belt of the Western Cape of South Africa, mainly in areas with a Mediterranean climate. Fynbos is known for its exceptional degree of biodiversity and endemism. As this floral community has the capacity to regenerate after fire it provides an opportunity to study the genesis of a variety of ecological phenomena such as hydrological niche segregation.

Species in plant communities normally separate along fine-scale hydrological gradients. Different plant species settle in different ecological niches based on the availability of water in the soil. One open question is at which stage of a plant's life history this segregation actually happens. one hypothesis is that it starts at the seedling stage because it is the most vulnerable as it is most prone to drought, competition, herbivory and disease. A group of researchers from the UK and Switzerland put this hypothesis to the test with a soil translocation experiment performed in the fynbos in South Africa, after a fire and before seed germination had started:

Following wildfires at two field sites where we had previously mapped the vegetation and monitored the hydrology, seeds were moved experimentally in >2500 intact soil cores up and down soil-moisture gradients to test the hypothesis that hydrological niche segregation is established during the seedling phase of the life cycle. Seedling numbers and growth were then monitored and they were identified using DNA Barcoding, the first use of this technology for an experiment of this kind.

The study focused on endemic species in the family Restionaceae because it is species-rich, ubiquitous, contains many keystone species and most species have been sequenced for the matK gene which is one of the plant DNA Barcode markers for plants.

According to the results of the study seedling growth on hydrological gradients in the field is affected by soil moisture status and by root competition. This means that hydrological niche segregation could indeed potentially originate in the seedling stage. In particular below-ground competition seems to be decisive in determining a species' hydrological niche. Fynbos species, as in other fire-prone plant communities, divide between those that regenerate from seed and those that resprout. The resprouters were probably the chief source of below-ground competition for seedlings in our experiment