Extreme Events

Before we round up our investigation into the numerous effects of climate change on flora and fauna and begin to look at the big picture of what the future holds for ecosystems and biodiversity across the planet, there is one more thing I would like to discuss with you.

Extreme events.

While I’m not here to talk to you about the X Games or something organised by Red Bull wherein someone jumps off a very tall mountain on a very small BMX, what I do have to say is nonetheless of the utmost importance. As all third-year geographers worth their salt know, climate change brings with it an increased frequency of extreme events. These range from drought, storms, flooding, wildfires and freezing all the way up to hurricanes, and can have devastating impacts for local ecosystems. As Shen and Ma (2014) point out, these extreme events affect the biodiversity of ecosystems directly through environmental changes to habitats, which can upset the balance within and between trophic levels and can cause dramatic shifts and changes to occur within food webs.

The ways in which the many varieties of extreme events affect ecosystems are too numerous to discuss at length here. Instead, I would like to leave you with an example, that, whilst not giving you a breadth of knowledge of the ways in which extreme events can manipulate ecosystems, will hopefully give you an understanding into how these changes may occur and the significance of the threat to biodiversity that extreme events create. I would like, then, to discuss Beaver et al.(2013)’s paper into the effects of hurricanes on a subtropical lake (Lake Okeechobee), specifically those upon its phytoplankton inhabitants.

Now, I know that yet again I am giving an example that lies outside Europe, however this time I can explain myself. There are only a small amount of studies that investigate the effects of increasing frequency of extreme events on biodiversity, and of the few I could find, Beaver et al. (2013) painted the best picture of the severe nature of these effects. As I learnt from Beaugrand et al. (2003) when constructing my previous blog, “A Codding Mess” (well worth a read), plankton and phytoplankton are hugely sensitive to climatic triggers, and hence offer one of the best examples when explaining impacts of changing climates. 

Between 2004 and 2005, Lake Okeechobee, a large freshwater lake in Florida, experienced three hurricanes which had dramatic effects on the biological communities that make the lake their home. Prior to the hurricanes, the phytoplankton communities in the lake were dominated by cyanobacteria (an algae of sorts that produces energy by way of photosynthesis). These organisms flourish under conditions of adequate access to light and a high nutrient content, which Beaver et al. (2013) consider the two fundamental determinants of the composition of phytoplankton communities.

The team of academics found however, that after the hurricanes had hit the lake, these cyanobacteria were replaced as the dominant biota (in terms of abundance) by meroplankton diatoms. They observed that post-hurricane, cyanobacteria of genera such as Anabaena and Planktolyngbya decreased in abundance by around an order of magnitude (tenfold), whilst meroplankton diatoms such as Aulacoseira spp. declined significantly less, by around 20%.

Although tiny, phytoplankon (and all forms of plankton) make up a significant portion of most marine ecosystems, and are depended on by predators all up the trophic level, as they are often among the primary producers in a food web.

Beaver et al.(2013) theorise that the variation in response to the hurricanes stems largely from a change in the environmental suitability of the lake for cyanobacteria in lieu of several habitat changes caused by the hurricane winds.  They point out that for lakes, hurricanes can often lead to mass incidents of sediment resuspension, alongside almost total destruction of aquatic vegetation, both of which contribute to the floating matter and causes a significant reduction in transparency. Increases in the availability of nutrients are also commonplace. In fact, for Lake Okeechobee, Beaver et al. (2013) observed that concentrations of NO₂ and NO₃ nearly doubled in the post-hurricane period, and Secchi disk transparency fell from 0.43m to just 0.21m (meaning a fall in water transparency). As cyanobacteria require high light attenuation to generate food, they find themselves somewhat at a loss in darker waters, hence why they suffered such significant reductions post hurricane. Conversely meroplankton diatoms, and diatoms in general, are more successful under conditions of low light and considerable turbidity, and so suffered considerably less decline.

Another effect of this increased turbidity and lower light penetration is that of increased predation. Beaver et al. (2013) argue that cloudier conditions supposedly offer more cover for crustacean zooplankton grazers, who otherwise would be more vulnerable to predation from fish and other biota gained a relative degree of concealment, benefiting population size and hence creating greater predation pressures for phytoplankton communities.

The impacts on biodiversity of these changes are quite severe. Beaver et al. (2013) calculate several indices of biodiversity for both pre- and post-hurricane Lake Okeechobee. The Shannon-Beaver biodiversity index (also known as Shannon’s H, which represents species richness) fell from 7.91 to 5.56 and the Simpson biodiversity index (which portrays the relative abundance of species) fell from 5.32 to 3.95.

It is clear then that extreme events can be devastating for ecological communities. As we have seen, extreme events can have massive effects on the environmental regime in an ecosystem, and can have significant effects on the fitness of species within the food web. This can damage biodiversity, as we have seen in Lake Okeechebee, reducing species richness and relative abundance. As we learn from Jones (2014) (and will discuss further next week), diverse and rich ecosystems are essential for promoting ecological resilience, so any reduction in either richness or abundance can put ecosystems at greater risk. 

Further study into the effects of extreme events therefore is necessary. This information could help us to understand how ecosystem dynamics will change in an anthropocene world where extreme events have greater frequency. It is clear these events will become significant structuring factors for many ecosystems, which will become more prone to food web disturbances and trophic reorganisations such as the ones we have discussed today. Comprehension is key for any form of management or restoration.

Next week, as we begin to round off our discussion, I would like to begin discussing the big picture for biodiversity and ecosystems in a climate change age. It is time to bring all we have discussed together, and look at what may be a potentially grim outlook for the future of our planet’s biosphere.

Synchronised Phenology and Climate Change – Part Three: A Range of Consequences

In my previous blog, “A Codding Mess”, we discussed one of the key implications that phenological change has for ecosystems. Specifically, we explored how such changes lead to desynchronization between trophic levels, ultimately reducing the efficiency by which energy is transferred up the food web and potentially destabilising ecosystems.

However, the effects of phenological change are not just limited to the relationships between organisms and their food sources; rather, these changes have a huge variety of effects on the relationships that exist between species and their biotic and abiotic environments, and it is these somewhat overlooked impacts which I would like to explore today.

To recap, the phenology of a species is the timing of an activity that has developed or evolved in order to synchronise life cycles with then seasonally changing availability of resources. Changing phenologies have been widely studied, although according to Lane et al. (2012), amongst other academics, this attention has focused mainly on the changing phenologies of avian species, as arguably these species are amongst those with the greatest sensitivity. An overlooked area of study, then, according to Lane et al.(2012), is that of the effect of phenological changes on hibernating species.

Hibernation is a survival response that is widespread amongst mammalian communities. Unlike their avian counterparts, who generally rely on migration in order to survive harsh winter conditions, hibernation has developed as what Lane ­etal. (2012) refer to as an “in situ” response for sedentary mammals to extended periods of low resource availability. The phenology of this hibernation, Lane et al. (2012) argue, can have profound implications for the consequent fitness of the animal in question, mainly through its influence over date of emergence. The researchers therefore highlight the effects of climate change on hibernators as a key area of study, in order to identify how these animals will be affected by changing climatic regimes.

The Columbian Ground Squirrel (Urocitellus columbianus)

In their study, Lane et al. (2012) attempt to begin a dialogue through their investigation into the effects of climate change on the phenology of Columbian Ground Squirrels (Urocitellus columbianus).  This species of squirrel have their habitat in the Rocky Mountains of North America, where the short growing season requires them to hibernate for around 8-9 months each year; the remaining time is split between mating (around 51 days) and then accumulating sufficient fat resources to survive until next year.

Delays in emergence then can have drastic effects on the fitness of these species. As they require 24 days for gestation and then a further 27 for lactation before fat reserves can be accumulated, any reduction in the time between hibernations can have serious consequences on their ability to accumulate sufficient reserves and hence survive the following period of hibernation (Lane et al. (2012).

Here, even though they have a relatively high degree of phenotypic plasticity, it seems that the situation is something of a “lose-lose” for the Columbian Ground Squirrel. During years of lower temperature and delayed snowmelt, which are becoming increasingly more frequent due to climate change, for phenology to remain the same would result in premature emergence, when snow cover still prevents access to sources of food for the species. However, the phenological plasticity of the species does it few favours either; by emerging later, the animals are effectively cutting short their active season. This is what is currently being observed by Lane et al. (2012), who note that hibernation emergence dates have been delayed by a period of 0.47 days a year over the past two decades, and this has resulted in consequent declines in mean fitness and population growth rates, a phenomenon that is set to only become more volatile over the next few years.

Another interesting study regarding the more unforeseen consequences of phenological change was published this year, authored by Stenseth et al.(2015). Through the analysis of four high-quality and long-term datasets, the group analyse the effects of climate change on the competitive relationship that exists between Blue Tits (Cyanistes caeruleus) and Great Tits (Parus Major) across Europe.

Climate change’s effects on competition can similarly have significant impacts for ecosystems. Competition, defined by Stenseth et al. (2015) as “the negative effects which one organism has upon another by consuming, or controlling access to, a resource that is limited in its availability”, plays a key role in ecosystem stability. Generally, within ecosystems, competitive relationships between species exist in a delicate balance that allows, to an extent, both to survive and reproduce without causing overt disruption to one another, whilst also preventing either species from becoming dominant (or creating a monoculture). This is the case in the majaority of ecosystems currently shared by Blue and Great Tits.

Here you can see the two engaged in something of a mexican stand-off

However, when you throw climate into the mix, as always seems to be the case, things get a little confused. This is exactly what Stenseth et al.(2015) found in one of their study locations. Through modelling how climate change will likely affect the parameters of competition models, they found that in Peerdsbos, Belgium, long-term climate changes would have a significant effect on the competitive interaction between the two species. Specifically, they noted that Great Tits generally would have greater abundance in cooler springs, and Blue Tits in warmer springs, and warned that these changes in population density may result in trophic cascades or even be the cause of future extinctions. Although Stenseth etal. (2015) cannot identify the specific mechanisms through which climate affects competition, the implications of this are serious enough to invoke further study.

By presenting you with these examples, I am trying to get across the point that the effects of climate change are incredibly pervasive and far-reaching. You can never take it at face-value, and the intricacies of its impacts are simply astounding. Some, when discussing phenological change, talk merely of desynchronization as the big issue, however as I have shown phenological change permeates every aspect of animals lives, affecting even their hibernation patterns and competition with other species. This point stands for all of the effects we have discussed, and throughout this entire blog I have tried to bring your attention to the otherwise overlooked impacts of climate change on our biota (such as this excellent blog on the effect of range shifts on genetics).

It is for this reason that extensive research into climate change and its effects on the biosphere are of critical importance. The effects it will have are so in depth and significant, that even with numerous dedicated teams of researchers we are still just scratching the surface. There is so much yet to learn, and if we ever hope to change the course climate change is taking for the natural world, let alone understand it, it is clear it needs to become a top priority.

Play Your Part - Nature's Calendar and Phenological Data Collection

In something of an aside, I’m here today to issue you a challenge, rather than shout at you about how climate change is ravaging ecosystems worldwide.

A few of the more avid ecologists amongst you will be aware of Nature’s Calendar, the organisation which manages, collects and facilitates the UK’s extensive phenological data sets. They rely heavily on citizen science to support their services, and currently receive phenological information from a wide range of volunteers across the country, with varying degrees of experience (Woodland Trust).

But they are in trouble. According to a news article by MarkKinver (2012), experts in the field are becoming increasingly concerned regarding the decline in the number of volunteers who record critical plant, bird and insect behaviour. Long-running data sets are becoming threatened, largely due to diminishing resources and information being provided to Nature’s Calendar.

Dr Kate Lewthwaitz, the project manager for Nature’s Calendar, tells Mark that the amount of expert and semi-expert recorders has taken a dive in recent years; where once they had volunteers in their high hundreds, now they have only about 200 left. Many of the volunteers are unfortunately becoming too elderly and are finding themselves unable to complete surveys and contribute to Nature’s Calendar. 

If you’ve been reading this blog then I don’t need to tell you how important these data sets are. Phenological studies are key to understanding how human-induced climate change is affecting species across the world. Scientists rely heavily on organisations such as Nature’s Calendar and the services they provide to direct and facilitate their studies. Without the understanding and appreciation for the problem generated by these investigations, we simply won’t have the platform from which to act to help mitigate against climate change and protect our valuable flora and fauna against the humongous challenges climate change creates.

That is why Dr Kate Lewthwaitz, in her interview with MarkKinver (2012), issues a challenge. And this challenge is to you. Dr Lewthwaitz calls for the next generation to pick up where the retiring experts let off, and to join the movement and support science through voluntary collection of data.

And you should really consider it. You don’t need to be an expert (although some of you reading this blog may just be) and you would be providing an invaluable service not only to science, but to the plants and animals you observe. We all need to pitch in to fight climate change, and if you feel this is your niche, you can see here for details about how to get involved.

Synchronised Phenology and Climate Change – Part Two: A Codding Mess

As we discussed in our last blog, the decoupling of phenological relationships can have devastating consequences for ecosystems. The internal dynamics within ecosystems and between trophic levels can be hindered and links between species effectively broken, having dramatic effects on the constitution of food webs and the internal stability and resilience of ecosystems as a whole (Edwards and Richardson 2004).

This is exactly what Beaugrand et al. (2003) believe is happening in the North Sea, where concerns are emerging regarding mass declines in the biomass and recruitment (when juvenile organisms survive and are added to a population) of Atlantic cod (Gadus Morhua) since the mid-1980s. Whilst admittedly linked to severe overfishing in the area, Beaugrand et al. also argue that fluctuations in prey species (plankton) of juvenile cod are severely reducing the survival of young. Beaugrand ­et al. suggest that the survival of larval cod relies heavily on three biological parameters of the prey plankton; their mean size, seasonal timing and abundance – all of which are undergoing heavy influence by climatic factors.

Atlantic Cod (Gadus Morhua)

In fact, the argument is such that the phenology of plankton species, which determines timescales of peak abundance, are being dramatically effected by changing sea surface temperature. Arguably, this reduces the number of prey for juvenile cod, resulting in reduced growth and consequently survival (Beaugrand et al. 2003).

A similar study, conducted by Edwards and Richardson (2004), expands upon this idea, and investigates the effects that sea surface warming of 0.9^oC over the past 60 years is having on different pelagic taxa that together facilitate the upwards transfer of energy to juvenile cod through the food web. Specifically, they look at diatoms and dinoflagellates (primary producers), copepods (secondary producers) and non-copepod holozooplankton and meroplankton (secondary and tertiary producers).

Edwards and Richardson (2004), by calculating the change in timing of seasonal cycles for each biota, observed what they describe as “substantial temporal modifications” in peak abundance over the past 30 years (a similar time-frame as that referred to by Beaugrand et al. 2003). Specifically, they found that the peak in meroplankton moved forward by an average of 27 days, dinoflagellates by an average of 23, copepods by 10 days and non-copepod zoo plankton by 10 days over the study period. Diatoms, however, had no significant advancement in their spring  bloom and only a relatively minor 5 days in their autumn bloom.

Here a few examples of the output from Edwards and and Richardson's (2004) study can be seen. a details the seasonal cycle of the dinoflagellate Ceratium fusus and the diatom Cylindrotheca closterium, and there is a clear pattern of change for the former and a clear lack of change for the latter. b shows how the interannual variability for seasonal peaks for the two species across the study period (note, diatoms have a spring and autumn peak, so show two peaks in the data). c shows the change in timing of seasonal peaks over the entire 45-year study period for the 66 taxa, against seasonal peak from 1958. Clear change is shown for certain taxa, whilst others, largely those belonging to diatoms, show little change.

Edwards and Richardson (2004) explain these advancements as a result of phenological change due to temperature increase; supposedly, temperature plays a key role in influencing plankton physiological, affecting a range of variables including reproduction, mortality, respiration, and embryonic development. It is for this reason that there has been significant advancement (of a greater magnitude, Edwards and Richardson argue, than studies have shown in terrestrial ecosystems)  in seasonal cycle in response to climate warming for large parts of the ecosystem. Conversely, diatoms have remained arguably stationary, leading Edwards andRichardson to believe that they are more dependent on the photoperiod or intensity to influence life cycles.

The issue arises from the variability in response that we see. Although a large proportion of the pelagic ecosystem IS responding, the intensity of this response is highly variable, and is leading to severe asynchrony between successive trophic levels. This creates inefficiency in the transfer of marine production to higher trophic levels, as peaks in species are no longer able to take full advantage of each other and transfer the most energy possible up the trophic level. Less production means less prey, and less prey can have dramatic effects on larger members of the ecosystem such as the Atlantic Cod (Edwards and Richardson 2004). This is the issue at hand; our fishy friend is currently being held hostage from the bottom up, in what Beaugrand et al. (2003) refer to as bottom-up control.

An understandably morose Atlantic Cod

This provides an excellent example of the dangers of phenological change, and really helps portray the intricacies of the problem. Note how all members in the study conducted by Edwards and Richardson experienced differing levels of advancement, making the problem of desynchronization not just a problem between one or two species, but between all trophic levels. This allowed change right at the very bottom of the trophic scale to affect a species that exists right at the very top, and everything in-between. This is dramatically destabilising for ecosystems, and if allowed to persist, could create great uncertainty in the future of ecosystems, and possibly lead to collapse.

In our quest for understanding, we will expand upon this more in our next blog. The issue here is huge, and there is a lot of ground to cover.