Synchronised Phenology and Climate Change - Part One: The Problem

The more avid blog followers amongst you will remember towards the start of this blog, when we discussed phenology. We discussed it with reference to our old friend the Pie Flycatcher (Ficedula hypoleuca), whom, according to studies by those such as Both and Visser (2001) and Goodenough etal. (2010), is falling behind the peak of food abundance due to diurnally triggered migration. Essentially, whilst the peak of prey species is creeping ever forward at home in response to increasing temperatures, the Pied Flycatcher is blissfully unaware and continuing to holiday in far flung regions, essentially getting left behind. In this and the next few blogs, I would like to take the opportunity to expand  upon this concept of phenology, exploring the important role it plays in keeping ecosystems functional, and offer a few examples as to how climate change, in a stunning turn of events, is throwing a spanner into the works.

I'm sure you remember our old friend the Ficedula hypoleuca

I would like to begin by briefly recapping on the concept of phenology, which was discussed so long ago and has been somewhat forgotten under the incessant waves of blogs exploring range changes and invasive species. Phenology, put simply, is the seasonal timing of certain events that occur in an organism’s yearly cycle.  According to Gienapp et al.(2014) phenology has incredible importance for the fitness of a species, as for most species there is a limited period wherein conditions are favourable for critical lifecycle events. Activities such as reproduction, hibernation and migration (as we have seen with the Ficedula hypoleuca) are essential for survival and proliferation, and can be at the mercy of how suitable a species phenology is to its surrounding ecosystem.

These ideal conditions can result from a variety of factors. Often they can be set by weather conditions, whereby a certain temperature or precipitation regime makes conditions favourable for specific activities. Other times, they can be dictated by the phenology of other species; this is typical in situations where predators are dependent on peak abundance of a certain prey species to enable energy-intensive activities such as breeding and rearing young (Gienapp et al 2014).

The essence of phenology

Generally however, the forces that influence phenology are climatic in nature. Due to year-to-year variation in the timing of certain climatic conditions, phenological characteristics that are directly or indirectly influenced consequently show a relative degree of plasticity – that is, are relatively flexible. However, the ability of ecosystems to adapt to short-term changes (those between years) is considerably greater than their ability to adapt to long-term changes, a phenomenon largely due to differential shifts across different trophic levels (Gienapp et al. 2014).

Species from different functional groups and trophic levels within ecosystems (essentially, those that perform certain functions or exist on different levels of the food chain) have experienced a varied magnitude of response to climate change, which over the years has caused significant advancements in phenology globally. These shifts, according to Gienapp et al. (2014), are typically more pronounced at lower trophic levels. Gienappet al. explain this variation as resulting from species reacting to differing environmental cues; for example, some species are sensitive to cues in separate periods (some species may be sensitive to winter peaks in temperature, whilst others to spring temperatures), whilst others are simply more sensitive to conditions such as temperature, with more of its functions influenced and hence will show greater plasticity. Some, like our unlucky friend the Pied Flycatcher, aren’t sensitive to climatic triggers at all, and instead rely on photoperiod (day length) triggers for phenology.

Phenology plays a critical role in all ecossytems - from the arctic to your back garden

Across the globe, this is causing huge problems for ecosystems. We are seeing increased instances of “decoupling” between phenological relations, which can cause mass disruption for trophic interactions through the altering of food-webs and can ultimately cause destabilisation of ecosystems. Studies such as those by Edwards and Richardson(2004), that investigates the effect of phenological shifts on pelagic ecosystems in the North Sea, and Visser and Holleman’s (2001) study on climatic effects on winter moth (Operophtera brumata) and Oak (Quercus robar) bud burst synchrony are two examples I will be discussing in the coming blogs that paint a very negative picture for the future of global ecosystems. We will also be exploring the range of effects that phenological change can have on inter-species interactions, such as what Stenseth  et al. (2015) investigate in their study on phenological effects on competitive relationships between Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major).

Over the next couple of blogs, I hope that we can really develop an appreciation for the extent of what is really a very intricate and widespread problem. Phenological asynchrony, like range shifts and invasives, present huge barriers for ecosystems, and require an indepth and intricate understanding if we are to ever do anything to minimise the impacts of change on the life of our planet.

Invasive Species and Hellmann's Famous Five - Part Two: Immigration and Impacts

Earlier this week we began the conversation about Hellmann et al.’s (2008) five predictions into how climate change will affect the proliferation and impact of invasive species. To recap, we discussed how climate would affect the way in which invasive species are transported and introduced to ecosystems and how climatic constraints on them would change, helping make them more successful and “putting a foot in the door” of previously highly resistant environs.

The time has come to finish the discussion, and bring our musings to a close. Today, we will discuss how climate change affects the distribution of invasives, their impact, and how easy they are to manage.

Climate Change and Altered Distributions

In this blog, we have extensively explored the topic of range shifts. It should come as no surprise then that the concept not only applies to native species, but also those with more invasive tendencies. For many invasive species, cliamte change brings with it an invitation to a range of new ecosystems and biomes. Europe alone for example saw its number of invasive species increase by 76% in just the last 30 years (Bellard et al. 2013).

Hellmann et al.(2008) expand upon this idea, stating that it is not only temperature change that will facilitate the spread of invasive species, but also the changing salinity of coastal estuaries, increasing wildfire frequency and soil moisture changes that will play a large role. Of course, we have seen numerous examples in previous blogs regarding changing species distribution. A meta-study conducted by Bellard et al. (2013) takes this further and examines how climate will change the distributions of what the International Union for the Conservation of Nature list as the "100 worst invasive species".

Using forecast projections derived from the species distribution models of the invasives, coupled with land cover and climate change scenarios, Bellard et al.(2013) uncover future hotspots of invasion (areas projected to see an increase of invasive species of >60). They found a general pattern that areas in the Northern Hemisphere were to become most vulnerable to invasions by the top 100, whilst tropical areas and other areas of extreme conditions (such as tundra and warm deserts) would generally be protected by their environments.  Within the Northern Hemisphere, it was found that biomes such as warm and temperate mixed forests would become most suitable for invasives (seeing a likely rise of about 4.5% of top invasives), as well as temperate deciduous forests. These predictions see large swathes of the eastern United States, North-East Europe, southwest Australia and New Zealand at particular risk.

These maps, from Bellard et al. (2013), show the distribution of the top 100 invasives globally in both the present and in future scenarios. Map (a) shows the richness of invasive species in 2000, (b) the relative change in richness between 2000 and 2100 (red meaning increase and green decrease), and (c)  the projected invasive species richness in 2100. As you can see, it is mainly temperate latitudes in the Northern Hemisphere that are most at risk.

An example of one invasive species making the most of its increased freedom is the infamous Yellow-legged Hornet (or Vespa velutina). Native to Southeast Asia, this hungry critter found its way into south west France and has since spread over 190,000km², even making its way to Northern Spain (Barbet-Massin et al. 2013). This invasive causes widespread damage to the ecosystems that it invades, primarily due to its predation upon honeybees (Apis) and attacks on colonies, which the poor honeybees have no real defence against, having not evolved alongside the invader. This predation has large knock-on effects for ecosystems, having considerable impacts on pollination and hence the ability of local flora to reproduce (Barbet-Massin et al. 2013).

This video below details the ruthless nature of the hornets predation on honeybees, and why they are such a destructive invasive. 

In order to assess areas that would become vulnerable to invasions under climate change, Barbet-Massin et al. (2013) modelled what the distribution could potentially look like in 2100, using several climate change scenarios. Their study found that there is very high probability that V. velutina will establish widespread populations across Western Europe, where climate and a lack of competition will allow the hornet to run rampant. Specifically, the areas found to be most vulnerable were large parts of Germany, Denmark, Poland, stretching even to Romania and parts of Scandinavia such as Southern Sweden. 

The area of climatic suitability for the Vespa velutina is set to dramatically expand by 2100 (Barbet-MAssin et al. 2013)

It seems then that climate change will loosen the reins on what are devastating species. This will put many organisms, both flora and fauna, in ever more vulnerable positions, which, combined with the difficulties caused by climate change alone, will make survival for species an incredibly difficult prospect.

Changing Impacts of Invasive Species

One of the most dangerous aspects of climate change for invasive species is the huge uncertainty in how it will affect their impact on ecosystems. As Hellmann et al. (2008) deftly point out, currently invasives have widespread effects on ecosystem structures, communities of organisms and even resource production (such as we have seen with the Yellow-legged hornet, which hinders pollination).  Arguably, the significance of this impact depends on a number of factors, such as the size of range of endemic species occupied by the invasive species, its abundance and it’s per unit-biomass impact. Hellmann et al. (2008) argue that as climate change is set to alter these factors, in ways that are far from easy to predict, thus making the impact of invasive species far more uncertain.

Whilst few good predictions exist of the changing impacts of invasive species, there are a limited number of studies that highlight potential situations. Seager et al. (2007), for example, discuss how the reduced precipitation pattern in the southwest United States (again I depart from our European focus, please forgive me) may affect the per-unit biomass impact of Tamarisk (Tamarix spp.), a family consisting of various shrubs and trees. According to Seager etal. (2007), they are more water intensive than native riparian species, meaning that, when combined with decreased water supply, their competitive impact will increase dramatically.

Here you can see Tamarisk itself, enjoying it's riparian habitat.

Changing impacts can obviously be a considerable threat for ecosystems. Where invasives already exert considerable pressure on environs, exacerbation of impacts by climate change could make challenges for native taxa ever more insurmountable.

Impact on Management Efficiency

Although this is somewhat removed from the flora and fauna focus that I usually enforce in my blogs, I felt it was necessary to touch on Hellmannet al’s (2008) last point that climate change may affect the efficiency of management techniques. Whilst in a large way this is a problem for humans (and hence none of this blog’s concern) as invasive species can be incredibly expensive, this can also present an issue for native species wherein conservation efforts are concerned. 

In some areas for example invasive species may be controlled by an artificially introduced predator or herbivore – however if climate change allows them to subvert these interspecies interactions, they may re-emerge as a highly problematic species. This also applies to other methods of management, such as the use of pesticides or other control techniques. Climate change can potentially make invasive species highly unpredictable and ergo incredibly difficult to manage. For the native species being protected, then, this is very bad news indeed.

Conclusions

Hellmann et al.(2008) paint quite the dystopian picture for the  invasive species/climate change relationship. Across the board, climate change can be seen to bring great benefits to them, by expanding their range (and their travel capabilities through new human movement), giving them a leg up against natives and making them even harder to get rid of. Invasive species come to the fight against natives with climate change as an ally, and it makes them far superior and far more dangerous.

Native species then are contending not only with one enemy, but two, and climate change is affecting them both directly and indirectly through proliferation of invasives. The picture at the moment seems so bleak, and I haven’t even reached the end of my list of topics to talk about. Is there a light at the end of the tunnel? I’ll guess we’ll just have to wait and see.

Invasive Species and Hellmann's Famous Five - Part One: Passage and Plasticity

Last week I began discussing the effect climate change will have on the proliferation of invasive species. We discussed two basic concepts; that of increasing ranges and climate change aiding successful invasions. This week, I’d like to take the opportunity to explore these concepts in a little more depth. Specifically, I’d like to discuss Hellmann et al.’s (2008) “Five Potential Consequences” of climate change for invasive species, and how it makes them a threat not only to native species but also to the biodiversity of ecosystems.

Firstly though, I feel it pertinent to readdress what we would call an “invasive species”. In a constantly changing ecological world, it can be hard to determine what species are invasive and which are not. The climate change induced range shifts of seemingly innumerable species only add to the confusion. Do these exile species count as invasives? In this blog, and all future blogs, I will be using what I find to be a very suitable definition of what counts as an invasive species; as Hellmann et al.(2008) so eloquently put it, an invasive species can be simply identified as “taxa that have been introduced recently and exert substantial negative impact on native biota, economic values or human health”.

As we learnt from Manchester and Bullock (2000) last week, invasive species can be incredibly harmful for native species and local biodiversity. Not only do invasive species outcompete and make vulnerable native species, but can also dramaticlly change the environmental regime, making enviurons ever more unsuitable for their original residents. But what makes them so successful? As Hellmann et al. (2008) observe, invasive species differ tremendously from those native to ecosystems.  Generally, invasive species have far greater climatic tolerances (and hence large geographic ranges), and often have characteristics that allow for rapid adaption, such as short generational times and rapid maturation of individuals. Some are also geared up for distribution, such as flora that feature low seed mass that can consequently travel greater distances.

Richards et al.(2006) portray a nice and succinct summary of the types of invasive species with their three (although very general) classifications. You have;

- The “Jack of all Trades”, essentially an invader which maintains fitness in a variety of environments
- The “Master of Some”, an invader that is able to actively increase its fitness in a few favourable environs
- The “Jack and Master”, wherein an invader has both of these abilities

Hellmann et al.’s(2008) idea is that essentially climate change affects invasive species in five major ways that are relatively unique to the ecological marauders. These include altering the methods of transport and introduction of invasives, altering the climatic constraints placed upon them, altering their distribution, altering their impact and finally altering the effectiveness of management strategies. Today I will be addressing the first two (the final three will be discussed in my next blog).

Altered Mechanisms of Transport and Introduction

Globalisation and increased human connectivity has had a large part to play in aiding the spread of invasive species. From Killer Shrimp (Dikerogammarus villosus) travelling to Britain in the ballast tanks of trade ships (Madgwick and Aldridge 2011) to Invasive Aquatic Plants being brought over as part of the plant trade and consequently escaping into the wild (Willby 2007), human factors play a large part in many invasions. Climate change, Hellmann et al. (2008) argue, has the potential to change these patterns of human behaviour, and hence the way that invasive species move around the globe.

This image, from the National Oceanic and Atmospheric Administration of the US, shows how ballast tanks can become transporters of invasive species

Hellmann et al. (2008) split these changes into three neat categories. Firstly, they see climate change altering patterns of tourism and commerce, meaning that we may see links starting to form between different geographical regions, opening up new areas to invasive species. They also argue that pathways of international transport could change; most obviously, if arctic sea ice experiences significant losses, the opening up of a viable Northern Passage will occur and will dramatically shorten travel time for some ships and hence increase the survival rate of invasive propagules or animals. Finally, Hellmann et al. (2008) predict that an increase in extreme weather events, such as hurricanes, could enhance invasive dispersal, as these events often carry birds, insects and marine larvae great distances from their native environments. 

The threat also exists for assisted migration. If humans were to begin to move organisms to new habitats in an effort to conserve species, they could potentially become invasive. This also applies to recreational assisted-migration, such as the transporting of fish for sport-fishing to new areas that are becoming climatically appropriate for the animals (Hellmann et al. 2008).

These consequences could have dramatic impacts on the number of invasions that occur. By improving chances of survivability and increasing the areas open to invasions, more ecosystems could be put at risk. This opens up areas to the increased competition rates, environmental impacts and even reduced biodiversity that destructive invasives can cause (Manchester andBullock 2000).

Altered Climatic Constraints/Climate-aided Invasives

Hellmann et al. (2008) also discuss how climate change can aid invasives in establishing significant populations. The group bring to our attention three key methods of how climate change can benefit invasives.

Firstly, climate change can dramatically increase climate suitability for invasives, who may otherwise be unable to establish successful populations in an environment. Climate change may aid in increasing their fitness to a point whereby they become viable competitors and can begin to successfully colonise the regions in which they find themselves. To give an example, plants and animals kept by humans which then escape, which before climate change would not be able to find a suitable habitat, may begin to establish populations.

Secondly, climate change may increase the fitness of invasive species relative to native species, which have effectively been shifted out of their optimum.  This process would dramatically reduce competition and make it far easier to invasive species to become dominant in their new habitats. This is demonstrated nicely by Knop and Reusser (2012) in their study of how phenotypic plasticity (the ability to respond to a wide range of temperatures) aided the Portuguese slug (Arion lusitancius) in invading the habitats of the native “Dusky Arion”, or Arion fuscus.

Here is the handsome chap himself; the Portuguese Slug

Through testing both species in a range of temperatures (using an altitudinal scale that ranged from 700 – 2400masl) and in low and high food conditions, they found that the Portuguese slug’s ability to adapt its behaviour to environmental conditions made it far more successful than the Dusky Arion. They found that across the temperature range the Portuguese slug had significantly higher survival rates, especially in areas that bordered on the limits to the Dusky Arion’s range. They also found that even in extremely low food conditions, the Portuguese slug still managed to reproduce, while the Dusky Arion laid no eggs at all. Knop and Reusser (2012) consequently argue that it is this ability to endure in a broad range of conditions (making the Portuguese slug, by Richards et al.’s (2006) classifications, a “Jack of all Trades”) that makes A. lusitanius such a successful invader.

Finally, Hellmann et al. (2008) also remark how changing climates may allow species that currently exist as non-natives in ecosystems to become invasive. They argue that climate change could effectively move these species closer to their optimal conditions, effectively increasing both their competitive ability and rate of spread. This could dramatically reduce the lag time of invasions (that is, the time between establishment of a non-native and, if it becomes invasive, its aggressive colonisation of the ecosystem).

These three changes dramatically increase the vulnerability of ecosystems to invasion by non-native species. Through changing conditions, climate change effectively allows invasive species to “get a foot in the door”, and dramatically increases the potential of invasive species to spread within ecosystems. This, as stated earlier, could have dramatic knock-on effects for the biodiversity of ecosystems, and the ability of individual native-species to survive in an environment that is open to invasions.

Unfortunately, that’s all we have room for this time. In the next blog, I will be continuing the discussion, talking about altered distributions, altered impact and the altered effectiveness of management strategies.

Invasive Species - Climate Change's own Migrant Crisis?

Invasive species have always been a headache for ecosystems and ecologists alike. Put simply, these invaders are non-natives; they are species that have colonised areas either through accidental human transport or through range expansion. And, living up to their name as “invaders”, more often than not they bring with them a whole load of problems.

Invasive species can have massive impacts on ecosystems, making them more vulnerable or reducing biodiversity. One of the most obvious is issues that arise from increased competition with native species for resources, a fight that, due to their highly adaptive nature, invasive species usually win. Invasives may also predate on native species, adding additional stressors that can cause populations to shrink. They can also have a direct impact on the environments themselves, through changing fire regimes, soil properties, vegetation structure and the water table, which can make habitats highly unsuitable for native species. Invasive species can even have genetic impacts through hybridisation with native species, which can affect fitness of native species to their environment (Manchester and Bullock 2000).

Such effects undoubtedly lead to severe ecosystem and biodiversity problems. This video below, from Augnitia, provides a pretty good summary of the effects that invasions can have both on individual species and on a macro-scale.

But where does climate change come into all of this? Many, such as Hintzen (2015) (in their academic article for Michigan State University) and Harvard Magazine (2010), believe that a link exists between climate change and the proliferation and capability of invasive species. This argument appears twofold; on the one hand there are those such as Nijhuis (2013) who see climate change as aiding invasive species in outcompeting natives through the changing of conditions, and on the other, you have those such as the National Wildlife Federation of America who see climate change as aiding in the spread of invasives through the landscape.

The idea that climate change and its effects on environs aids invasive species is not unfounded.  Hintzen (2015) notes that, due to climate change, growing seasons are becoming extended and extreme storm events are becoming more frequent and are growing in intensity. She argues that these factors create stressors for both native and invasive species alike, however suggest that invasive species are generally much better equipped to deal with said stressors. This arguably stems from what makes invasive species so successful in the first place; invaders generally have the ability to adapt quickly to new environments and conditions. As Nilhuis (2013) explains, they are highly flexible, with generally short generation times, high dispersal ability and show rapid responses to changing environments. This means that invaders are far more able to adjust to changing timing of annual activities such as blooming and fruiting (hence showing far greater phenotypic plasticity), allowing them to capture a larger share of nutrients, water or pollinators whilst shading out the competition.

One such offender is none other than Purple Loosestrife (Lythrum salicaria)

One such invasive that has done just that is the Purple Loosestrife (its business name is Lythrum salicaria). This plant adapted rapidly to sync its flowering schedule with the lengthening growing season in the UK, allowing it to outcome natives who generally show a much slower response.

Range shifts, which we have been talking about in excess over the last few weeks, are also understandably beneficial to invasive species. By opening up more areas where these species can persist, climate change also makes a lot more areas susceptible for invasion. The National Wildlife Federation for example lists numerous cases of invasive species rapidly expanding their range in the wake of a changing climate (please forgive the American examples; this is supposed to be a Euro-centric blog).

The Deer Tick (Ixodes ricinus), for example, is expected to increase its range by up to 68% in North America due to milder winters. Similarly, the Red Imported Fire Ant (Solenopsis Invicta) could expand its range by 80 miles and total area by 21%. Cheatgrass (Bromus tectorum), is also set to expand as long as summer precipitation continues to decline. The estimated expansion is around 45%, and could make habitats more susceptible to wildfire. Furthermore, Pine Bark Beetles (of the sub-family Scolytinae) are predicted to undergo a population explosion due to the absence of severe winter cold, and threaten to migrate northwards, causing the untimely demise of many healthy trees as they go (Mersereau 2014) (National Wildlife Federation).

A more European example is that of the Arctic Fox (Vulpes Iagopus). These animals, which are highly adapted to severe arctic conditions, find their southern boundary determined not by climate but by competition, mainly from their cousin the Red Fox (Vulpes vulpes). For the Red Fox, their northern boundaries are determined instead by harsh conditions. In the event of climate change, therefore, it is estimated that the range of Red Fox will expand northwards and consequently that of the Arctic Fox will decline (Elmhagen et al. 2015).

The Arctic Fox's southern boundary is limited by competition - meaning that if its main competitor, the Red Fox can advance north, it will be forced to retreat in response.

The effects of climate change on invasive species then are twofold. The friendship that climate change provides to a large amount of invasives however is to the detriment of the majority. As Charles Davis (in Harvard Magazine 2010) aptly put it, “climate change will lead to an as-yet unknown shuffling of species, and it appears that invasive species will become more dominant”. Whilst some will thrive, most will fall, and with them, so will the resilience of ecosystems and the state of biodiversity be called into question. This is something I look forward to exploring in more detail in the coming weeks.