'Nature’s mechanisms ensure rich plant diversity — climate change is impacting these'

Meghna Krishnadas is senior scientist at the CSIR Centre for Cellular and Molecular Biology (CCMB), India. Speaking to Srijana Mitra Das at Times Evoke, she discusses why plant life is so varied, what threatens this now — and why that will affect human lives
What is the core of your research?
Our Community and Functional Ecology Lab is broadly interested in understanding which processes in nature help maintain diversity in ecological communities. Diversity can be understood as the number of species in a setting, abundances therein or characteristics of species which are also called ‘traits’. We see large and small-sized birds, for instance, some eating fruits, others insects, etc. Similarly, a forest contains plants with different kinds of leaves — we research why there are so many varied leaf types, why some trees are larger or smaller and some fruits are coloured differently. We examine diversity in all these facets, exploring why one or two species don’t just push all the others out. We also use principles of ecology to research how human actions are changing ecosystems today — and what that means for diversity.

YOURS TRULY: We are linked to rivers. Photo courtesy: iStock
Why are some plant species rare?
There can be historical factors here — some species which evolved in biogeographical timescales grew to have a very small population, needing a certain habitat or a particular resource, even just one kind of pollinator, which is only available sporadically. This can also be about ecological consequences — certain species aren’t good competitors compared to others.
They tend to be pushed into niches or situations where their numbers stay low. Rarity itself is a two-edged sword — it allows for greater diversity in an ecosystem but rare species also tend to be most at threat globally when habitats get fragmented or humans alter natural systems. We research whether there are certain inherent features associated with rarity — we find larger-bodied species, for instance, are often rarer in the plant world.

A WORLD OF VARIETY: From grasses, scrub and shrubs to saplings and trees, forests house a dazzling multiplicity of plants, carefully regulated by nature. Photo courtesy: iStock
Which natural mechanisms keep such rare species functioning?
Ecological theory suggests rare species stay in a community if there is a feedback mechanism which allows them to escape competition. Plants compete with each other — but many mostly compete within their own species as opposed to between these. Even when plants compete between each other, they have natural enemies like pests, parasites, pathogens and predators that are specialised on certain species — when a species grows more abundant, its pests and pathogens bring its numbers down.
As the host grows, so do its parasites, thereby cutting back the species from proliferating more. The flipside to this is that the rare species gains an advantage — it can’t be found by its own pathogens so quickly and easily. We call this ‘density dependence’ which means mechanisms in nature ensure a population’s growth rate is greater if it is rare. As long as these are intact, rare species can stay in a community and diversity can be maintained. This is the basis of the co-existence of species. Data and mathematical simulations in our research now show that as forests get fragmented, they lose density dependence and thus, diversity. This matches with real-life scenarios where fragmented patches have low diversity or species which tend to go extinct over time.

SMALL HERO: Fungi aid biodiversity: Photo courtesy: iStock
How does rainfall impact interactions between plants?
A plant in a neighbourhood is surrounded by members of its own species as well as others. If there is density dependence, whenever its own species’ numbers increase, a plant will be hit more negatively and be less likely to survive. This gives rise to population regulation. Not all places are equally amenable to these processes though — a cold or dry place isn’t as conducive to pathogens as a warm or wet site.
The feedbacks that cause strong density dependence regulation wouldn’t have evolved as powerfully in such habitats — hence, the ability of communities to maintain diverse populations there is limited. New studies show that even in a tropical forest, in years of less rainfall, like many places now, feedback processes between plant neighbours can weaken. In times of climate change with less rain, the plant world’s ability to ensure diversity can get compromised.

Forests are often considered remote to urban life. How correct is that notion?
This is a great misconception — the simplest connection between cities and forests is water. Many rivers that maintain our water supplies originate in forests — if we keep fragmenting these, it will impact the hydrological cycle and the quality and quantity of water. Cutting down forests also contributes to emissions, climate change and extreme weather events — these affect cities as well. By destroying nature’s mechanisms, we are reducing Earth’s ability to deal with higher carbon concentrations.
Thus, what happens to forests does impact urban residents — citizens should take some responsibility for ensuring ecosystems maintaining forests and water security are preserved. We can make a difference by becoming more aware of the wider natural world and the connections between our own lives and ecosystems. We should also be more mindful about using essential resources like water — and we should encourage our leaders to organise better public transport systems and other measures that can help us reduce our carbon footprint.