When we talk of biodiversity, one of the first associations is with a diverse range of different species – plants, animals, birds, insects and even microorganisms. The same way of thinking came to my mind as well before discovering the hidden aspect of biodiversity, called ‘seasonal biodiversity’. But while learning it, I discovered the fact that nature has a ‘changing’ story! For instance, a tree, animal or any form of life can be completely different in different seasons. Birds can come and go, a new set of flowers can bloom, amphibians can thrive only upon appropriate rainfall, insects can emerge at a particular temperature, etc. Even microorganisms in oceans have seasonal patterns. It is clear that biodiversity is not only about the species diversity but also about their presence in a particular season and their interactions with other organisms. This pattern is called seasonal biodiversity. Further we can link this concept with phenology – the study of patterns in nature.
A Closer Look at Seasonal Biodiversity
Seasonal biodiversity can be explained very simply with examples. A number of species react to environmental cues at different points of time. These cues may include temperature, rainfall, day length, humidity, snowfall, river flow, etc.
For instance, birds can show up when the season changes, a tree can give a new set of leaves or flower, amphibians like frogs can begin reproducing after rainfall, a particular type of insect can emerge when the temperature allows, or mammals can change their coat throughout the year! What I find fascinating about these examples is that the events are not isolated but form a chain.
Let me elaborate it with an example – a tree flowers at a particular time of the year. Bees are dependent upon the flowers of this tree, while the birds are dependent upon the bees which further means their dependency on this particular tree. It means a change in one can lead to change in another. Thus, a season is not only a change in temperature or rainfall but a change in links or connections as well.
Seasons and Ecosystems
The phenomena differ in various parts of world. For instance, in temperate zones we see the change of seasons; in tropics, change is less in temperatures but may be well seen in dry and wet seasons.
India, for instance, is a classic example which shows the effect of monsoon on biodiversity. With arrival of monsoon, the breeding of frogs and toads begins, plants shed their leaves or start flowering, termites and winged ants appear, animals change their habits or locations, etc. During the dry season, leaves of some plants turn yellow and many animals move towards water and food sources.
Even leaves lying on the ground have a role to play; they are decomposed by fungi and bacteria and further enrich the soil. Thus, the seasonal pattern of a tree can change the links of the food web in the soil. This implies that seasons not only influence, but can regulate the ways of an ecosystem.
Microorganisms in Ocean – Seasonal Diversity of Rare Things?
One of the most surprising discoveries for me was the seasonal patterns in microorganisms. Microorganisms are rarely considered or studied, although they are vital components of marine or any ecosystem. According to ‘The study of seasonal marine metagenomics’ – out of 83 seasonal bacterial lineages only 4 were both seasonal and abundant while 59 were permanently rare.
When we talk of diversity, we refer to species and their abundance; the rare ones are neglected. However, it is vital to know that rare species can play key roles as well. This could be the reason why the abundance of a species cannot be the only criterion to study biodiversity.
Plants, Salty Habitats and Monsoon
Saline habitats are tough to live in but there are some plants, called ‘halophytes’, which are adapted to such environments. With arrival of monsoon, the salinity decreases and plant diversity further changes. The major point here is the availability of natural water bodies. Their anthropogenic disturbance can disturb the seasonal patterns of plant diversity.
This fact made me associate this knowledge with a practical application – how a simple disturbance in availability of water can change plant diversity.
Flowers, Pollinators and Mismatch
The example which is the best illustration to explain seasonal biodiversity and phenology is the relation between flowers and their pollinators. In the case of Corydalis ambigua, the flowering plants are visited by bumblebees. With advancement of snowmelt, the flowering period of this plant advances as well. However, if the advancement of bumblebee pollinators does not match the advancement of these plants, there could be a ‘phenological mismatch’.
This term simply means that the two partners, dependent on each other, are not synchronized anymore due to a mismatch in their advancement. It could be compared to arriving at a shop, where you had previously planned to meet someone, but on reaching the shop you learn that the person has left.
Birds, Insects and Mismatch again?
The same mechanism of response to environmental cues further leads to the consequences for other animals.
Many bird species depend on insects for their food supply and hence, need to synchronize accordingly. However, climate change can make the phenology of plants and insects mismatch with the phenology of birds. The consequence is that the birds will not be able to utilize the resources for breeding. This is also studied under the same concept of ‘match–mismatch relationship’. Similarly a change in plant phenology leads to consequences for caribou, roe deer and Arctic geese as the plants change their availability and nutritive value in different seasons.
This example makes a very strong impression on me as it shows that only a few weeks difference in seasonal patterns can be devastating for an animal dependent on this particular resource for a short time period.
Insects and Their Calendar
Insects are one of the most interesting components of biodiversity with seasonal patterns. For instance, temperature can be an indicator of insect appearance or their diapause. Some insects appear in specific seasons or produce a specific number of broods depending upon the temperature. Thus, a warm season can change more than the seasonal pattern – it can change the whole strategy of an insect’s life cycle.
These consequences can be very serious – especially in case of agricultural pests. Such insects can appear to damage the crops long before their expected appearance. This can be devastating for farmers. On the other hand, the warm season can also encourage more and faster breeding of beneficial insects, like pollinators. Even honeybees change the proportion of workers and their lifespan according to seasons. This is yet another reminder that an ecosystem is never static.
Food Web and Seasons
While thinking of a food web, the first picture that comes to mind is the diagram with arrows showing the predator-prey relationships. However, the same is not true for different seasons. For instance, the interactions between Piper amalago, a plant, and insect herbivores can vary greatly between rainy and dry seasons. Thus, the same set of organisms in two different seasons can interact in completely different ways. Similar patterns were also observed in coastal sediment communities. Today, scientists can even take the help of technologies like hyperspectral remote sensing to study seasonal patterns in functional characteristics of the ecosystems.
The reason to highlight such studies is that one cannot simply count species to claim to have studied biodiversity in two different ecosystems. Two forests may have almost the same number of species but these species may have completely different roles in the two ecosystems in different seasons.
And the Streams?
Another interesting study is a study on macroinvertebrates, conducted on a karst stream of southwest China. The study focused on changes occurring in the community structure and biodiversity during normal, dry and wet seasons. It concluded that these variations could be attributed to water condition changes. One of the most important conclusions was that biodiversity cannot be measured based on only taxonomy – three types of diversity (taxonomic, functional and phylogenetic) may show different trends.
In simple words, two seasons may have almost the same number of species but these species may have different roles (functional diversity) in the two seasons.
This is yet another concept that can be applied while studying the biodiversity in a region. For instance, one can make monthly visits to a stream or a pond and study the changes in the plant, insect, bird and even water diversity. Such a pattern will surely give a picture of the seasonal biodiversity in this particular region.
When the Seasons Get Confused?
Today the major threat to seasonal biodiversity is climate change. With global warming, springs are likely to start earlier in many areas and winters are likely to start later and be less severe. Monsoons will be erratic with some areas facing drought while the others will have flooding. The important point is that different species will respond to these changes differently. A tree may respond to temperature while an insect may respond to changes in day length, a bird may respond to food availability and so on. Eventually, this will lead to a situation comparable to the ‘phenological mismatch’ but at a much larger scale.
Urbanization is another factor which can interfere with the phenology. Cities tend to be warmer than the surrounding landscapes due to the urban heat island effect. As a result, the timing of ecological events may shift in urban areas.
Sometimes the results can look quite surprising – for instance, dragonflies usually appear in summer; if they appear in late autumn, it will be alarming for scientists. Similarly, fish usually leave the spawning grounds to move to deeper and colder waters with the onset of winter. If this movement does not happen, it can be alarming.
How To Save Seasonal Biodiversity?
I think that the conservation of seasonal biodiversity does not require any big or sophisticated measures – the first step is to know what has changed. This requires phenological studies – recording the dates of flowering of plants, migration and appearance of birds, breeding of frogs, emergence of insects, monsoon advance and retreat, etc. Citizen science can also play a great role in the collection of such phenological data.
Further, the conservation of habitats is no less important. Wetlands, forests, grasslands and streams are crucial for the survival of many species.
The preservation of seasonal flow of rivers is also crucial. Corridors for safe migration of animals and minimization of use of pesticides are also helpful. The maintenance of different habitats is important too as it will give more options to species to survive if their habitat changes. It is necessary to remember that conservation planning is as much about time as it is about space.
When designing protected areas, it is not enough to simply consider the spatial structure. It is necessary to carefully account for the temporal structure as well. This means that, for example, a forest must be protected not only on the map but also the critical seasons for breeding and flowering must also be taken into account.
Conclusion
To say the truth, the concept of seasonal biodiversity made me reevaluate my understanding of biodiversity. If before I thought of it only in the context of diversity of species on a particular area, now I realize that it is a complex system which works on a complex set of rules. Flowers bloom, insects emerge, birds appear, frogs breed, leaves fall and microorganisms change their activity according to cues in environment. These events are not isolated but are connected and can affect each other. Climate change is disturbing this delicate mechanism and making the system unstable. Different species respond differently to temperature, rainfall, day length or any other cue. This can lead to the disturbance of interactions between species, which had developed over long years.
However, I find that we do not have to look far to study such seasonal changes; every garden, pond, tree, roadside plant or stream can be our object of study. We can see how flowers bloom, how insects emerge, how birds appear and how these changes gradually occur throughout the year.
Thus, the concept of biodiversity is not only about the list of species but also the story about how these species are changing with time. It made me realize that not only the species and their habitats need to be protected but also the natural rhythms which bind them together. This is why seasonal biodiversity is truly nature’s changing calendar.
By: Ankur Yadav
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