Impacts of Natural Disasters on Ecological Balance – An Original Perspective

In this essay, I will try to present this topic in a different way – an original perspective of looking at ecological balance, which is, like a more complicated and intricately tuned version of a balanced chemical equation of a reversible chemical reaction in a dynamic equilibrium, and how perturbations like natural disasters can affect this delicately established equilibrium. According to the latest hypotheses, the origin of life took place as a set of closely occurring biochemical reactions. Therefore, since life is deeply rooted in chemistry at the molecular level, I have used a similar perspective to look at the macro-world interactions and events. 

Firstly, in order to understand what the implications of natural disasters on ecological balance are, let’s know what the terms mean. Hazard is an event or an agent that has the potential to harm a vulnerable target, and it becomes a disaster only when it actually harms the target. They can either be natural or anthropological. Natural disasters can be further classified as geophysical (earthquakes, landslides, tsunamis, volcanic activity), hydrological (avalanches, floods), climatological (extreme temperatures, drought, wildfires), meteorological (cyclones) or biological (disease epidemics, insect/animal infestations). 

 Fig 1: A schematic depiction of environmental systems (like, ecosystem) as open systems. Such systems have a high-quality energy input (generally abiotic sources) and discarding low-quality outputs (on degradation of dead living forms).

Ecological balance can be conceptualized as a state of dynamic equilibrium within communities of organisms in which genetic and species diversity remain relatively stable, but is subjected to gradual changes through natural succession over an evolutionary timescale. This implies that there is an existence of co-ordinately varying parameters of population dynamics of each species. Most of us are familiar with balancing chemical equations. We do this so that we get an idea about the effect of change in each chemical species on the overall equilibrium of the chemical reaction. Ecological balance can be conceptualized in a similar way as balanced chemical equations, if not the exact same way. Let’s understand this comparison in a more detailed manner before we proceed any further. I will be trying to draw three important analogies between a chemical system and an ecosystem to finally give meaningful shape to this topic. 

Each chemical species in a given equation of a reversible chemical reaction can be compared to a biological species in a given ecosystem. Whenever we study equilibrium of a chemical reaction, we talk about the number of each chemical species present in that system (as concentration is the number of molecules or members of a certain species in a given volume or per unit given volume). Similarly, we talk about the number of each member of a species within given geographical boundaries whenever we analyse equilibrium in an ecosystem. Furthermore, thermodynamically, chemical reactions also tend to proceed in such a way as to increase the total entropy of the system. Entropy generally increases in reactions with more product species. Although I am not defining reactants and products from an ecological perspective, it can be said that in both cases, there is a flow of energy. More distributed the energy is, more stable is the system, whether it be chemical or biological. Therefore, intuitively it can be said that more the number of species in a given ecosystem, more stable it is.

Fig 2: Energy Flow Network in an ecosystem. All flows are in kcal/m2/year. Biomasses are in kcal/m2. Green arrows are energy inflows into ecosystem network boundary from external sources (generally abiotic). Black arrows are exports of useable energy (from biotic to the abiotic space). Red ground symbols represent metabolic energy loss (used up for sustaining life)
Fig 3: Network and network measures of an ecosystem model. a–e, Illustrative network (a) and network measures (b–e; Extended Data Fig. 1). (b) Total energy flow (g m−2 d−1) is the sum of energy flows Fi that passes through the system (including energy flows that enter the system). (c) Flow uniformity (unitless) is the ratio of the mean (m) of summed flows Fi through each trophic compartment i to its s.d. (standard deviation) (d) Total-network standing biomass (g m−2) is the sum of standing biomass Si across all trophic compartments. (e) Community maintenance costs (d−1) is the ratio of respiration Ri to community standing biomass. The dotted lines show ecosystem boundaries. The grey-shaded nodes and arrows are not included in the calculation of the respective network measure.

This is often ecologically said as, greater the biodiversity of an ecosystem, more stable is the ecosystem. Lastly, there are often examples of chemical reactions that can occur only in a coordinated fashion with another reaction(s). All reactions can occur only when a certain energy barrier/hill is crossed. Sometimes there are reactions that are not energetically favourable, but still, they need to occur and do occur in nature. It can be seen that energy from some other closely occurring chemical reaction has been transferred to this energetically unfavourable reaction, and with that contribution, they can finally occur. Such combinatorial reactions are very important and prevalent in nature. This is a common scenario in biological systems where reactions occur very closely, and there can be a transfer of energy from one reaction to the other. Now, going back to ecosystems, such compensation and coordination are seen at different levels of an ecosystem. Ecological interactions, for example, mutualism, commensalism, parasitism, etc., can all be analysed in a similar fashion, if thought deeply. These are few of the analogies that I have realised over time, while studying both chemistry and biology, which, I believe, are not coincidental, but fundamental. Let’s proceed to see how these analogies are relevant to the main theme of the essay. 

Assuming that the considered reversible chemical reaction takes place in an open system, i.e., both exchange of energy and matter is possible between the system and the surroundings (like, a chemical reaction in a beaker without lid/cover), we can compare it better with ecosystems, which are generally open systems. Open systems are more vulnerable to perturbations. Natural disasters are nothing but perturbations to the ecosystem. It often removes a certain number of individuals in a species or may remove certain species away in extreme cases. They can also cause a shift in ecological niches which might cause niche overlap and ultimately result in competition for common and limited resource and result in similar events of species removal. Now, whenever we remove a certain number of molecules from a chemical reaction, i.e., perturb the reaction system, there is a shift of equilibrium whose direction and consequences depend on the chemical species removed. Similar equilibrium shifts are observed in ecosystems in the aftermath of a natural disaster, which also depends on the species removed (for example, if a carnivore is removed, the equilibrium shifts towards more successful herbivory considering that the prey of the carnivorous predator is a herbivore).

The shift and the outcome might be more catastrophic in the case of an ecosystem than a reversible chemical reaction. It totally depends on the extent of species removal due to the catastrophe. However, an ecosystem with more biodiversity can be more resistant to such perturbations. Having multiple species present in a community can stabilize ecosystem processes. During environmental fluctuations, an increased abundance of one species can compensate for the decreased abundance of another. Likewise, with increasing biodiversity, there is an accumulation of more diverse traits/attributes which might help a species survive the catastrophe, adapt to the aftermath, and replenish the void, re-establishing ecosystem stability. 

Fig 4: Effect of increasing biodiversity on ecosystem stability, and its resistance and resilience components. Plot (a): Biodiversity consistently increases ecosystem stability  Plot (b) : Biodiversity consistently increases ecosystem’s resistance component to environmental fluctuations (perturbation)  Plot (c): Biodiversity do not increase resilience component (recovery after loss due to some catastrophic event, i.e., environmental fluctuation). Lines are mixed-effects model fits for each study (a), or each climate event within each study (b,c) (thin lines), or across climate events and studies (thick lines with bands indicating 95% confidence intervals). Thick lines and bands in (c) indicate trends averaged across both moderate and extreme events for either dry (dashed red lines) or wet (solid blue lines) events. Stability measures are unit-less. Axes are logarithmic.

Energy flow in an ecosystem occurs through the food chains and the food web. Unlike simpler chemical models, that we study or we have assumed above, energy distribution and energy flow in an ecosystem are like a network with nodes, hubs, and edges. Each species occupies the nodes or the hubs and their ecological connections are denoted by the edges. More ecologically connected, and hence, more important, species are at the hubs of such an energy network. Displacement of any of the nodes or hubs cause edge disconnection – energy flow is affected. This destabilises the system. The energy sources are abiotic. This energy can not only sustain us but also destroy us. For example, the sun gives us solar energy that plants take up directly and transmit it up the food chain – sustaining life. However, energy transfers in natural disasters like tsunami, earthquakes, etc. (where the energy comes from heated energy sources beneath the earth’s crust) can destroy life. This, again, indicate the vulnerabilities of an open system like the ecosystem.

Fig 5: Trophic network models for communities with low (1 species) and high (60 species) plant species richness and the differences among them. The areas of the circles are scaled by the square root of standing biomass. The values associated with each circle show the actual standing biomass values (g m−2) and s.e.m. The widths of the arrows are scaled by the square root of energy flows. Data are averages for all of the monocultures (n = 14) and all 60-species plots (n = 4), respectively, that were plotted in this experiment (see Extended Data Fig. 4  of the paper by Buzhdygan, O.Y., et. al. 2020). Right, the differences in standing biomass (circles and the numbers associated with each circle) and energy flows (arrows) for the model for high compared with low diversity levels. The orange circles and arrows show negative differences and, therefore, lower values at high diversity than at low diversity. The blue symbols show positive differences and, therefore, an increase in values from low to high diversity. The graphs were generated using NodeXL (Image and caption sources are given at the end of this blog)

A severe catastrophe might lead to a total crumble, and the birth of a new ecosystem might follow over evolutionary timescales. More than 99% of all organisms that have ever lived on Earth are extinct. This doesn’t mean that there has always been a more or less a continuous trend of change in the rate of species extinction throughout history. There have been several discontinuities, which are popularly known as mass extinctions. The most recent one happened around 66 million years ago, which is called the Cretaceous-Paleogene extinction event. It is connected to a major asteroid impact, which took away approximately 76% of all species on the planet, including all non-avian dinosaurs. This is how extreme natural disasters can be. 

Fig 6: Mass Extinction

By now, I think, we know why I was drawing an analogy between a reversible chemical reaction in an open system and the ecosystem, to better understand how ecological balance works. However, both have their distinctions and exceptions that make them unique. Also, we have discussed the severity of natural disasters and their impact on ecological balance. As a concluding note, it can be said that while natural disasters are not in our control, what we can at best do is trying to preserve the biodiversity of the planet as much as possible. Like we have discussed before, that is the best that can be done to bring back ecological stability after a natural disaster disrupts the ecological balance. Perhaps this is why it makes so much sense to celebrate the World Environment Day this year with the theme of ‘Celebrate Biodiversity’, as declared by the United Nations.

By,

Diptatanu Das

Department of Biological Sciences

IISER Kolkata

Featured Image by,

Prince Roy

Department of Earth and Environmental Science

IISER Kolkata

Theme of the Featured Image: Doomsday (An Asteroid Attack)
Achievement: World Space Week 2015 Edition National Award )

Source of the images:

Fig 1: Fath B.D. (2012) Ecosystem Flow Analysis. In: Meyers R.A. (eds) Encyclopedia of Sustainability Science and Technology. Springer, New York, NY. doi: 10.1007/978-1-4419-0851-3

Fig 2: Fath B.D. (2012) Ecosystem Flow Analysis. In: Meyers R.A. (eds) Encyclopedia of Sustainability Science and Technology. Springer, New York, NY. doi: 10.1007/978-1-4419-0851-3

Fig 3: Buzhdygan, O.Y., Meyer, S.T., Weisser, W.W. et al. (2020) Biodiversity increases multitrophic energy use efficiency, flow and storage in grasslands. Nat Ecol Evol 4, 393–405. https://doi.org/10.1038/s41559-020-1123-8

Fig 4: Isbell F, Craven D, Connolly J, et al. (2015) Biodiversity increases the resistance of ecosystem productivity to climate extremes. Nature. ;526(7574):574‐577. doi:10.1038/nature15374

Fig 5: Buzhdygan, O.Y., Meyer, S.T., Weisser, W.W. et al. (2020) Biodiversity increases multitrophic energy use efficiency, flow and storage in grasslands. Nat Ecol Evol 4, 393–405. https://doi.org/10.1038/s41559-020-1123-8

Fig 6: http://bio1520.biology.gatech.edu/biodiversity/mass-extinctions-and-climate-variability-2/


About the author:

Diptatanu is a third-year BS-MS student at IISER Kolkata and a KVPY fellow, majoring in biology, with a chemistry minor. He has been a part of the gold-medalist iGEM IISER Kolkata teams in 2018 and 2019, and is also associated with this year’s team. Other than having a high affinity for good food and sleep, he loves to make music and play TT, football, cricket, etc., in his free time. He prefers to do some original work and has been writing articles, blogs and composing new songs. He is also one of the admins and a regular blogger of our blog page, ‘The Qrius Rhino’.

Read his other blogs for TQR: Dragon’s Triangle – The Pacific Ocean’s Deadliest Enigma, How Good Is Gaming?, [email protected], A Dream within a Dream, iGEM in India!, Coronavirus – An Unsolvable Challenge? and A Summer in Germany!

Author: Das Diptatanu

Diptatanu is a fourth-year BS-MS student at IISER Kolkata and a KVPY fellow, majoring in biology, with a chemistry minor. He has been a part of the gold-medalist iGEM IISER Kolkata teams in 2018 and 2019, and is also associated with next year’s team. Other than having a high affinity for good food and sleep, he loves to make music and play TT, football, cricket, etc., in his free time. He prefers to do some original work and has been writing articles, blogs and composing new songs. He is currently the CEO of IISER Kolkata Campus Radio and is also one of the admins and a regular blogger of our blog page, ‘The Qrius Rhino’.

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