Tag Archives: ecology

Natural wonder: Sir David Attenborough

Happy Birthday Sir David Attenborough! As I am sure we all know, last week marked this great mans’s 90th; a person who has more than anyone changed our relationship with the natural world, enthusing countless generations to appreciate the variety of life on our planet. His dedication, passion, relentless enthusiasm has undoubtedly inspired more people in our world to care and want to make a difference. I certainly am on this pathway because of him as well as other incredible individuals (including my mum!).

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SO what makes him our natural treasure?

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1# His enthusiasm

From collecting fossils as a child in Leicester, to loving creatures big and small, ugly and beautiful, his appreciation for all animals is why we love him so. He even says he is no animal lover, much to the bewilderment of many. However he is the ultimate curious intellect and shares a fascination for all of nature, and not the gushy anthropomorphic rantings of a bunny hugger…

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2# His knowledge

Not only has he racked up 32 honorary degrees from Universities across the country (more than anyone else), but having studied natural sciences at Cambridge then Anthropology later…his knowledge of all living creatures and the biological, chemical, physical process that govern them is second to none. Go on, ask him a question!

SIR DAVID ATTENBOROUGH

3# THAT voice.

His dulcet, hushed tones, as well as powerful vocals mix into just about the most recognizable natural history narration voice of all time. David = Nature God. His warmth and clarity both hooks and fascinated you. I think I’ve spent most of my waking life listening to his voice either through the television or radio podcasts. I’m even starting a petition for a David Attenborough Tom Tom guide…

“..And here, we have the Lyre bird…”

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4# Humble by nature

Despite his numerous awards, degrees, honours..he still remains a humble and grateful being…he loves economy class and never forgets to greet or thank you…

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5# He’s been there for you: in B&W, Colour, HD, 4K, 3D and 360 baby

He is the only person to have produced television in B&W, Colour, HD, 4K, 3D and more recently with his VR dinosaur 360 video clip. He’s so with it  even us youngsters have to keep up with him. I reckon a holographic projection David will be available soon…

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6# Impact

Sir David Attenborough joined the BBC as a trainee in 1952, and his early career included the highly different television debate programme, Animal, Vegetable, Mineral? But his audaciaous and determined nature meant that he wanted to show audiences new ways of making films and a life outside the television studio. The result was the hit series ‘Zoo Quest,‘ which combined live studio presentation with footage shot on location for the first time. He made us CARE about the natural world through education and entertainment. 

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7# He’s SO quotable

A master of verbal carpentry, his written scripts result in some memorable quotes, here are my personal faves;

“A hundred years ago, there were one and a half billion people on Earth. Now, over six billion crowd our fragile planet. But even so, there are still places barely touched by humanity.”

“Our planet may be home to 30 million different kinds of animals and plants. Each individual locked in its own life-long fight for survival.”

GO on, give us another…

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8# His wicked sense of humour

We’re no stranger to his witty, whimsical and wicked sense of humour. He’s been asked onto several major chat shows more than twice and his gentleman like attire and charm  is irresistible. Even Cameroon Diaz can’t get enough of our David! More recently during an interview on BBC Radio One, Sir David was asked to narrate the video for Adele’s new song. He even gave it the trademark Attenborough voice-over.

“Like all pop stars, she needs to hunt to survive,” he begins. “The lesser spotted Adele is about to be everywhere again.”

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9# He’s travelled more than anyone in history

Since his television career back in the 1950’s he started travelling around the world, and is now the most travelled person in the HISTORY of mankind...that’s some impressive migrating. It seems his life has been perfectly timed where he saw the world in its former pristine self… And so he’s not only just seen more wildlife, people and places than anyone else but also witness the greatest amount of change than anybody who has ever lived.

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10# He’s simply the best #WishYouWereMyGrandad

All that said, we simply love him because he is our natural treasure and we all want him to be our grandad…he started the beginning of natural history filmmaking, and still is an amazing filmmaker and producer in his own right…love you Dave’s XOXOX

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Here I write about my own encounter with the lesser spotted David, over 2 years ago…..

It was 6am, Spanish time. And yes, it was the summer, BUT Sir David Attenborough tickets were on sale for his lecture on Alfred Russell Wallace in Cardiff New Theatre! I was poised with my mouse cursor ready to buy a ticket after refreshing the page… then to utter dismay all the tickets had sold out after 2 minutes of pending. I was overwrought. It happened by coincidence that I had a week long field trip to Dale Fort, in Pembrokeshire on the 18th September, and the very same day that David was giving his lecture, and so I had to book a ticket! So I put my self on wait list and hoped for the best. After a week, forgetting that I had even applied, I received an email saying I had 2 places to book tickets-result! Booked them instantly….then I thought about actually getting there.

 

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So bunked off the uni bus journey to go and see my hero- and the reason why all zoologists study their degree… so a pretty good excuse! It took 7 hours in total to get to Cardiff Central, with various stop-offs. Wasn’t cheap getting there but I had worked as a student ambassador to get the money. Went with a friend, and we went for a coffee opposite the theatre at 6pm to await the arrival of the greatest wildlife broadcaster to have ever lived…That hot chocolate tasted so good! I was positively jubilant! I could not contain my excitement as soon as I had received the lecture brochure and meticulously read through the talk. Then we walked out of the coffee shop, and at the same time a dark Mercedes tinted windowed car pulled up alongside the entrance, where he stepped out…I almost fainted on the spot then and there… He had entered the building!
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When we got our seats, which were at the very back, (so we could go out and catch the train we had booked to go to Milford Haven, then to our field trip location) and then as Sir David entered there was a sudden gasp from the audience, followed by a rapturous applause! It was a fascinating lecture all about the great Alfred Wallace, and his humble beginnings and shear enthusiasm for adventure really. Some really hilarious clips and gestures by David, absolutely brilliant, wish all lectures were like this! Before I knew it, it was question time, I was the first to put up my hand, but sadly, at the back I wasn’t noticed until the end when they ran out of question time. They even handed me a microphone, at which point my legs had turned to jelly. After that, we had to rush out to get our bags and then run for the train, only just made it! Onwards to Dale Fort for our own adventures (and a lot of hard stats and collecting data from the field!). However, I did send him a long letter including the question I so wanted to ask, which was,
“Out of Darwin, Gregor Mendel and Wallace, who do you believe has contributed the most to society.”
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He answered back too! His letter takes pride of place on my windowsill, (next to my fossil Archaeopteryx). I think its wonderful that a man who is so busy would even take up his time to read his fans letter, he truly is a remarkable, special man, and I am honoured to have seen him at his lecture and be alive during his lifetime- Thank you David- and may you long keep making Natural History programmes!

Urban Ecology and Impacts on Bats

Okay so bats might not seem frightfully important to us…surely they’re nothing more than flying rats? You’d be mistaken! These incredible mammal species are a highly evolved flying and echolocating species- the only ones to do so. They ensure our skies aren’t ridden with biting insects, prevent crop damage, provide medicine in the form of draculin, give vision to the blind and lets be honest, MAKE Halloween! I conducted 10 months research on them a year ago, and here’s what I found out about how our urban lifestyle is impacting them in the UK.

Importance and impacts of an urban landscape on bats: Urban foraging

Each bat has evolved is perfectly adapted to each habitat, in terms of wing morphology, diet (ecological niche), echolocation call, hibernacula and behaviour (Altringham, 2011; Threfall et al., 2008). Thus, it is of vital importance to study the effects of particular habitat features on bats, as each specie uses the landscape differently (Altringham, 2011, Coleman & Barcley, 2011).

Some exhibit behavioural plasticity and can adapt to urban environments, enabling them to effectively exploit their habitat without the disruption of roads, light pollution or buildings (Russo & Ancillotto, 2014; Stone et al., 2011).

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This has been seen in bats with long narrow wing morphology with a high wing loading, as open air foragers are largely unaffected by urbanization (Norbeg & Rayner, 1987).

The ability of synanthropic bats to dominate urban foraging areas can be problematic for the less well adapted species (Silvis et al., 2014, Russo and Ancillotto, 2014). Urbanization may result in greater competition between the synurbic and less well adapted species. Arlettaz et al., (2000) suggested that the decline of Rhinolophus hipposideros in Wales may be due to the expansion of Pipistrellus pipistrellus, whose populations have increased as a result of greater feeding efficiency with artificial lights normally avoided by the lesser horseshoe bat (Warren et al., 2002; Lacoeuilhe et al.,  2014).

Water in urban areas

Bats are vulnerable to evaporative water loss as a consequence of their morphology and large surface area to volume ratio (Razgour et al., 2010). Within urban areas, open artificial sources such as ponds, ditches and swimming pools provide bats with fundamental opportunities to drink and forage.

Certain species show preferences over these larger, less cluttered and open bodies of water (Seimers et al., 2001). The reduction in pulse-echo overlap, ability to detect spectral shift and high insect abundance over still water sources can attract large numbers of bats to urban and modified sites (Altringham, 2011).

Such examples can be seen in North Carolina, where studies looking at the importance of managed water bodies over natural wetlands revealed significantly higher bat activity by heliponds, despite equal densities of insects at both sites (Vindigni et al., 2009). Equally, studies on Greek islands showed that bats will also use artificial water sources such as swimming pools due to the lack of natural sources in such arid habitats, with minimal annual rainfall (Davy et al., 2007).

So this Halloween, cast a glance into the skies at night and spare a thought for this remarkable little evolutionary quirk of nature…

Urban Bat Ecology

 Urban Growth

The rapid global urban population growth seen in the last 65 years, from 746 million to 3.9 billion in 2014, has had significant impacts on bat species richness and abundance (WUP 2014, Kunz et al 2007), due to habitat loss, fragmentation, degradation (Altringham, 2011), chemical pollution, barrier effects, introduction and facilitation of invasive species and a decline in prey species (Wickramasinghe et al, 2004, Lentini et al, 2012, Berthinussen & Altringham, 2012). Many studies are currently looking into the possibility of using bats as bioindicators of environmental change (Wordley et al, 2014, Russo et al, 2014), due to Chiroptera being the world’s second most speciose mammalian order (second to Rodentia), numbering 1232 species (Kunz et al, 2011).

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Equally, their widespread distribution and sensitivity to even minute perturbations means they could reflect the status or possible risk of such change in other species (Jones et al, 2009). Some of the responses to change can be seen with declines in abundances, population size, range distributions and behaviour (Altringham, 2011). Thus, it is important to determine the relative abundance of bats in urban areas compared to rural and suburban, and see whether an association with particular urban features are limiting or enhancing their ability to forage and roost there. This information has vital applications for conservation, as 82% of the UK is urbanised and is steadily increasing (United Nations World Urbanization Prospects, 2015). Thus, policy makers with knowledge regarding the ability of certain bat species to adapt (synurbic), or not (more vulnerable and sensitive species) to one of the greatest land use changes seen in the last century, can act to reduce the impact by lobbying with businesses, developers and politicians (Altringham, 2011, Russo, et al, 2014).

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Importance and impacts of an urban landscape on bats- Urban foraging and roosting

Bats form some of the largest seen mammalian assemblages, (Jones et al, 2009), with up to 40 million in a single cave-roosting colony (Seimers et al, 2001). The potential of urban areas being suitable areas to provide bats with useable roosting and foraging habitats is becoming an ever more prevalent area of research. Thus, it is of vital importance to study how bats are using such anthropogenic landscapes (Bellamy et al, 2013). It is essential that research from a wide variety of urban landscapes is conducted in order to assess the relative importance of particular variables and landscape features, as some are more important to different species, which each exploits the landscape differently (Altringham, 2011, Coleman & Barcley, 2011). It is this specificity of each species responding to urbanization differently which is vital to conservation and management policy. Each bat has evolved is perfectly adapted to each habitat, in terms of wing morphology, diet (ecological niche), echolocation call, hibernacula and behaviour (Altringham 2011, Threfall et al 2008). Thus some exhibit behavioural plasticity and can adapt to urban environments, enabling them to effectively exploit their habitat without the disruption of roads, light pollution or buildings (Russo and Ancillotto, 2014, Stone et al, 2011). This has been seen in bats with long narrow wing morphology with a high wing loading, as open air foragers are largely unaffected by urbanization (Norbeg & Rayner, 1987).

Hunting phases of bats. Search phase involves a high frequency component (45-55kHZ) as well as CF constant frequency with longer pulses as it detects prey. Then the calls increase in frequency with additional harmonic components as the bat approaches its prey. Then terminal phase the bat can emit calls at 2ms as it hones in on it.

The ability of synanthropic bats to dominate urban foraging areas can be problematic for the less well adapted species (Silvis et al, 2014, Russo and Ancillotto, 2014). Some studies even suggest urbanization may result in greater competition between the synurbic and less well adapted species, as implicated by Arlettaz et al (2000). The study suggested that the decline of the Rhinolophus hipposideros in Wales may be due to the expansion of Pipistrellus pipistrellus, whose populations have increased as a result of greater feeding efficiency with artificial lights (Warren et al, 2002, Lacoeuilhe et al, 2014), normally avoided by the lesser horseshoe bat. Equally, in one study investigating the activity of insectivorous bats in Panama Canal, it was shown that only a few dominant Molossus were able to adapt to urbanized areas due to their high wing loading and aspect ratio (Jung et al, 2011). This was in contrast to a majority of clutter-specialist species recorded which foraged within the forest and the forest edge.

Advantages provided by artificial roosts in urban areas include homoeothermic benefits, in particular for pregnant females by reducing the energetic costs of maintaining their body temperature within the thermal neutral zone (Lausen & Barcley, 2006). Therefore the potential to provide bats with artificial roosts is of interest to many conservation bodies, which aim educate and encourage public concern (Altringham, 2011). Artificial bat boxes have been shown to be particularly exploited by opportunistic and synurbic P.Kuhii (Angelli et al, 2011). However, the lack of rigorous scientific testing of their effectiveness is yet to be determined in lesser adapted species (Altringham, 2011), and with thorough monitoring and further studies into ‘bat box’ preferences, a more valid account of their potential use may be of value to policy makers (Russo & Ancillotto, 2014).

Importance of Water in urban areas

Bats are vulnerable to evaporative water loss as a consequence of their morphology and large surface area to volume ratio, as well as high energetic costs with the ability to fly (Razgour et al, 2010). Within urban areas, open artificial sources such as ponds, ditches and swimming pools provide bats with fundamental opportunities to drink and forage. Certain species show preferences over these larger, less cluttered and open bodies of water (Seimers et al, 2001). The reduction in pulse-echo overlap, ability to detect spectral shift and high insect abundance over still water sources (Altringham, 2011) can attract large numbers of bats to urban and modified sites (Vindigni et al, 2009). Such examples can be seen in North Carolina, where studies looking at the importance of managed water bodies over natural wetlands revealed significantly higher bat activity by heliponds, despite equal densities of insects at both sites (Vindigni et al, 2009). Equally, studies on Greek islands showed that bats will also use artificial water sources such as swimming pools due to the lack of natural sources in such arid habitats, with minimal annual rainfall (Davy et al 2007).

If you want to find out more about how YOU can help bats, head over to the Big Bat Map and the Bat Conservation Trust!

http://www.bigbatmap.org/pages/help-count-bats.html

Darwin VS Mendel: Scientist showdown

‘Who has made the greatest contribution to biology, Gregor Mendel or Charles Darwin?’

There is no doubt that the irrefutably intrinsic contributions of both these remarkable scientists enabled future generations of scientists to make further advances in biology which has shaped our lives worldwide; but to what extent does Charles Darwin’s theory of evolution and natural selection or Gregor Mendel’s set of laws of inheritance outweigh each other in terms of importance?

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Charles Darwin (1809-1882) was ‘a man born to explain the astonishing diversity of life and in doing so would revolutionise the way in which we see the world and our place in it.’ Indeed a revolutionary biologist, his pivotal idea was to be inspired on his journey to the Galapagos in 1835 aboard the HMS Beagle. Darwin collected a plethora of different species and meticulously noted minute differences between the species of the Galapagos and the mainland of South America. The evidence suggested that each species had not been independently formed by a creator but had diverged from a smaller group of common ancestors within the major animal kingdoms (Bowler 1983). His ideas of natural selection developed during 1837-1838. The proposed theory stated that in all species limited resources lead to a struggle for existence either between or against other species members, this is known as intraspecific and interspecific competition (Fullick 2008).

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Variation within species influences the success of an organism; therefore species with more advantageous ‘variations’ will live to reproduce and pass on these useful characteristics to their offspring and will better enable it to survive in its particular environment; this is natural selection (we now know that variation in genetic terms means advantageous alleles which occur due to DNA mutations, gene flow and sexual reproduction). This process over time would lead to the elimination of the lesser adapted species and the survival of the better adapted ones and possibly a new species (this is known as evolution, however, Darwin did not directly call his theory this).

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It took 22 years after his voyage to the Galapagos, armed with a wealth of knowledge and a mountain of evidence to publish the world-famous Origin of Species in 1859 (Shanahan 2004). It is clear today that the extent of Darwin’s contribution of his theory of natural selection has greatly contributed to biology. We are now fully aware of the interconnections between species and how we evolved over time. This also lead to the discovery of continental drift, the ‘missing links’ within our earths history through fossil records, the age of the earth itself and inspiration for other biologists. Professor John Shine from the Garvan Institute of Medical Research stated that “Darwin’s theory was a fundamental building block for all modern biology…underpinning the way we think about a lot of medical and biology research” (Arnott 2009). Also in agreement of Darwin’s achievements is Professor Tim Flannery who concluded that what Darwin has done for modern science and indeed every living individual on the planet is “give us the context that created us” and I am inclined to agree with both leading scientists (Arnott 2009).

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However, many critics of Darwin argue that his contribution was not as great as that of Mendel’s and that Mendel was the ‘father of genetics’ (Mawer 2006). Gregor Mendel was an Austrian monk and biologist who experimented with peas. Quite like Darwin, he was a nature enthusiast and studied at the University of Vienna before returning to priesthood in the Augustinian abbey (Montgomery 2009). It was at the abbey where he began his famous experiments with peas. Between 1856 and 1863 he grew and observed more than 28 000 pea plants and identified seven characteristics showing discontinuous variation including flower position, pea colour and pod shape (Fullick 2008). He experimented by crossing the pairs of peas and recorded which characteristics were passed down onto the next generation, later presenting his results to the Brunn Natural History Society. In 1866 his papers on the subject were published describing the two fundamental laws of hereditary; these are known as Mendel’s Laws of Segregation and Independent Assortment.

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Mendel helped us recognise how organisms passed on their traits to their offspring. His idea of genes was as “discrete particles passed on intact from parent to offspring” (Walsh 2012) and although his great achievements were not noted until 16 years later by Hugo de Vries and Karl Correns, the significance of Mendel’s discovery has enabled our modern society to function as his research laid the foundations for the study of genetics. The Human Genome project for example was created as a multinational project to determine the base sequence of the human genome and many new ones have been identified such as those responsible for disease (Skinner and Lees 2009) which has lead to the development of target drugs benefiting millions globally. Mendel had read Darwin’s theory with interest but pivotally disagreed with the blending notion (Pangenesis- where both parents contribute fluids to the offspring containing the genetic material which is blended to create the new offspring, Walsh 2012) and this is the main reason for many why it was Mendel who was the greatest contributor to biology as he had no ‘gaps’ in his evidence (Leroi 2009). However, I would argue that although Darwin had difficulty in comprehending inheritance, part of his genius was to realise that not understanding inheritance was not a predicament for his theory of natural selection and he had sufficient evidence for it from his work on domesticated animals and plants as well as from communicating with other scientists.

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The world’s most influential biologists, “Darwin and Mendel were contemporaries to many and yet the initial acceptance of their ideas suffered very different fates” (Walsh 2012). Darwin theorized evolution and its complex traits (concepts from population and quantitative genetics) whilst Mendel was concerned with the “transmission of traits from a genetic basis.” Combining Darwin’s theory of evolution with Mendel’s genetics was the most important breakthrough in biology as it triggered a cascade of a whole host of other biological discoveries including DNA (Mayr 1997) the understanding that bacteria evolve which has enabled us to devise methods of dealing with the diseases that they causes and also the disentanglement of the complex relationships between animals and plants within communities enabling us to foresee some of the consequences when we start to interfere with them. I have found both these remarkable scientists profusely influential in my life and to many of my heroes. I therefore collectively deem both of these extraordinary biologists of equal importance in their contributions to biology, because not only have they revolutionised modern biology, they have inspired countless generations to further pursue  scientific knowledge, which is fundamental to the survival, well-being and enjoyment of future generations to come on an ever-changing planet.

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However, our planet is changing. Although natural phenomena have always influenced our climate, the surmounting evidence is unequivocal – Homo sapiens’ ignorance and reckless activities have caused a colossal shift in the natural order and balance of our ecosystems and inevitably the animals that previously co-existed within them. Threats such as climate change, the introduction of invasive species and habitat loss have decimated animal and plant species numbers over the past 100 years to such an extent that nevermore so has the study of zoology been pivotal in understanding the complex interrelationships between specie physiology, behaviour, evolution and development in order to protect their very existence. To be able to understand the intricate relationships animals have within their environment and observe their interactions within it is truly a blessing. I have been enchanted by all organisms from a very young age; to study them in depth would be a privilege and would give me the opportunity to return the same fulfilment by protecting them for future generations to see.

Major threats facing keystone species and the consequences for biodiversity

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Tania R.E –Esteban 1

School of Biology, Faculty of Biological science, University of Leeds, UK, LS2 9JT

 

The global threats facing keystone species is significantly impacting levels of biodiversity, due to the disproportionate effects keystones have on entire communities. They influence trophic interactions and provide ecosystem services of vital importance to the economic, social and cultural well-being of humans. It is therefore in our interest to establish the threats, the individuals most at risk, the potential cascading effects on ecosystems and how we are to manage them successfully in terms of reintroduction or mitigation. In this essay I review the major threats to a variety of different keystone species (at all trophic levels), examine how this influences levels of biodiversity and what effects they have on entire ecosystems. I also evaluate the current and potential management strategies that facilitate networks and allow them to be more resilient to future environmental change. Our knowledge of the concepts that underpin the fundamental basis of ecology can help us confront this as one of the greatest challenges in ecology.

Concept of Keystones

In different ecosystems, each specie plays a role within a community and can influence levels of biodiversity. However, the relative impact of each species can vary in terms of importance [27]. Such species that have disproportionate effects on ecosystems are known as keystone species [39]. According to network theory, keystones are intimately linked via ecological networks of highly connected and complex webs (Box 1, [9]). These include species at different trophic levels. Apex predators exert top-down effect on these levels, known as trophic cascades; whereby these strongly connected species indirectly influence community structure and ecosystem function [37]. The robustness of food webs to species removals varies, depending on the species and ecosystem type, where certain removals have greater impacts on ecosystem functioning and structure. Many apex predators are classed as keystone species because of the secondary extinction impacts of their removal on other species [7]. Predators directly impact upon herbivore numbers as well as indirectly through risk effects [34]. This then influences the relative abundance of producers- hence a ‘cascading effect.’

trophic cascasde

Equally, predators sustain levels of biodiversity via the suppression of other competitors (mesopredators) through competitive exclusion, and allow other species to co-exist [20]. Predatory release occurs when the apex predator is removed, increasing populations of the less competitive mesopredator. This then leads to a decline in its prey. Predator-prey dynamics as well as competition between intra and interspecific species also influence the structure of the food webs [1, 27]. The length of food webs can also greatly influence the direction of the cascade according to the exploitation ecosystem hypothesis [11]. These natural processes can be perturbed by threats to apex predators- whereby the removal of such keystone species leads to the concept of trophic downgrading [10]. As well as this, there is an alternate stable; where ecosystems are disturbed to such an extent that the cascade shifts from its prior state to another- when a tipping point is reached [10].

Box 1- Network theory

The fragile nature of ecosystems has been explored by Sole and Montoya [36], on the basis that if the nodes that connect individuals are randomly removed in a network, it remains stable. However, when highly connected individual are removed, this results in cascading effects and interference throughout the rest of the network. These keystone individuals form the framework and structure of the network. In real ecological networks, strong evidence for the removal of predators are known to not only directly impact its prey, but also have indirect effects via top-down forcing. Ecosystems processes such as primary production, nitrogen cycling and the establishment of invasive species are also affected (Figure 3 [10]).

network theory

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Keystones – threats to a complex web of interactions

Habitat destruction

There have been major declines in biodiversity within recent decades, in what has been described as the 6th mass extinction event [27]. The threats facing keystones and the ecosystem services they provide are predominantly anthropogenic [19], and habitat loss is arguably one of the greatest [15]. For example, the Yellow and Black-Casqued Hornbills are both in decline, which has been correlated with deforestation in Nigeria as well as forest sections along the Ivory Coast [28]. This is problematic in that the genera Ceratogyma are key seed dispersers of fruiting trees, and play an important role in maintaining the heterogeneity of forests and species diversity via gene flow [28]. Because of the large spatial distribution of their territories [45], up to 22% of lowland tropical rainforest species are dispersed by the 3 hornbill species within this genera [23]. Cultural ecosystem services include traditional ceremony wear as well as other benefits to the keystone tree species, Ficus, which in turn provides economic services to local tribes’ people. It is also an important food source for other species within the ecosystem [23].

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Urbanization

Other threats to keystones include the urbanization of many habitats. Increased contact between humans and species drive them to exhibit behavioural plasticity and alter their behaviour [33]. A majority of studies indicate that increases in urban environments decreases species richness [35], due to disturbances in breeding patterns, anti-predator behaviour, fitness, selection of habitat and overall population size. This has cascading effects along trophic levels [2]. The black-tailed prairie dog, a keystone specie, contributes to the health of steppe habitats by mixing the soil. This increases plant productivity and landscape heterogeneity as well as providing coyotes with a food source [3]. Their overall numbers have decreased as a result of increased urbanization. However, in contrary to the risk-disturbance hypothesis, where increases in anti-predatory behaviours (such as vigilance) are seen, some populations exhibiting behavioural plasticity have reduced their vigilance due to habituation [12]. This has negatively impacted the vegetation due to increased foraging time, which has ‘rebounding’ effects back up the trophic cascade, on other herbivores and predators [33].

Climate change

Complex plant-pollinator webs are also disturbed by habitat destruction due to their sensitivity to perturbation [29]. This is the case with the keystone plant mutualist, Heliconia tortuosa,

Figure 1. The warming trend set to continue: (Left) Projected increases in temperature by 2081-2100 if mitigation and use of renewable resources is adopted. (Right) These are the predictions if the business as usual strategy continues (source: IPCC, Fifth assessment, 2014).

IPCC

which supports a variety of hummingbird species, and is considered a central node in this web interaction [17]. Recent work has provided evidence for the fragmentation hypothesis, where forest composition is fundamental to the reproduction of H. tortuosa. Thus, the reduction in heterogeneous landscapes due to deforestation is thought to alter both plant distribution and pollinator behaviour, leading to declines in both populations [29]. Equally, other systems have also shown that deforestation alters pollinator behaviour. Phaethornis hummingbirds will take longer flight paths to avoid deforest patches and agricultural landscapes, decreasing pollinator efficiency. This affects the survival of plant species dependent on this mutually beneficial ecological interaction- and has led to regional declines in biodiversity [16].

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Climate change also poses a major threat to the biodiversity of keystone pollinators (such as bats, bees and birds [19]). One third of the world’s crop production is met by the ecosystem services provided by insect pollinators [30], with agricultural pollinator services estimate to be worth £120 billion per acre, annually [40]. Phenological shifts are also increasingly being observed, with the impact evident in both pollinator and plant keystone species [4]. In Japan, seed production in Corydalis ambigua and Gagea lutea decreased due to the warmer temperatures causing them to bloom earlier, resulting in phenological mismatching with its key pollinator, Apis Mellifera. Consequently, this reduced pollination efficiency and success [31]. Climate change has also altered bee distributions and caused phenological shifts in their flight period. Predictions suggest that the spatial shifts in bee movements will be faster than that of its food resource, also causing phenological mismatching and decrease wildflower pollination [4]. Therefore, climate change poses not only a threat to the keystone plant-pollinators, but to other communities dependent on wildflower meadow species [31]. This highlights the fragility of these mutualistic interactions as key nodes in an ecosystem, due to their varying response to temperature change.

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A major issue with climate change is predicting the influence it will have on biological communities in the future [13]. The polar bear (Ursus maritimus) is an apex predator in the Arctic ecosystem which is very sensitive to changes in sea ice cover, where it hunts, migrates and reproduces [25]. The rate of temperature increase in the Arctic and northern regions have doubled in recent years, reducing sea ice cover [24]. In particular, over the past 30 years, the Western Hudson Bay has seen earlier ice break up as well as reduced snow fall (Figure 2). The impact on ringed seals (a keystone specie) with longer ice-free summers has subsequently lead to changes in polar bear behaviour [25]. The continuity of this pattern threatens seal pup survival as they are forced to swim for longer periods of time in open water, exposing them to predation [13]. Ringed seals provide polar bears with net wet weight calorific gains of 2.2-5.3 kcal/g [43], and the decreased recruitment of ringed seals has driven polar bears to target nesting birds, as they are unable to gain sufficient energy [25]. This warming trend is set to continue with possible increases in temperature of 5.0-6.4˚C by 2081-2100 (Figure 1, [24]).

Figure 2: Sea ice extent between 1979-2012 throughout the summer months. Evident loss seen annually. (Source: Iverson [25]).

Hunting and over-exploitation

Hunting and over exploitation is also a prevalent threat to many keystones worldwide. The removal of a keystone predator is a major cause of secondary extinctions, demonstrating the strong influence of top-down effects on lower trophic levels [10]. This was seen with the expatriation of the Grey wolf in Yellowstone during 1935 (due to hunting), which increased populations of elk as a result of predatory release [39]. Increased levels of browsing on aspen, cotton and willow saplings in riparian river systems led to a more homogenous landscape and reduced diversity [34]. The wolf played a vital ecosystem role by maintaining diversity as well as healthy numbers of mesopredator populations. Classic studies of the consequences of predator removal are also illustrated with sea otters [10]. Enhydra lutris was nearly hunted to extinction by Russian fur traders at the beginning of the 20th century, resulting in the predatory release of sea urchins, which reduced Kelp forests by intensively over-browsing [42]. However, with the return of the otter during the 1970’s to certain areas, the recovery of the kelp forests was observed due to the effects of top-down control on urchins. The kelp populations in regions where otters were unable to recolonize did not recover [11], demonstrating how the impact of hunting can alter and result in the simplification of food webs.

orca

The general pattern of global declines in apex predators is a cause for concern, due their strong connectedness in ecosystems and influence in altering the stability of food webs [19]. This is less well studied in marine ecosystems [20]. For example, sharks are apex predators in marine ecosystems [22], and are threatened by hunting. Demand for shark fin during the 90’s increased mortality rates by 80%. Many debate the function of sharks as keystone predators [8], however more recent studies suggest that although not all shark species can be described as keystones, some are key in structuring some ecosystems [44]. Indeed, strong arguments made by Estes et al., [10] concluded that the top-down effects exerted by apex predators are equally as influential as bottom-up effects. In Western Australia, Tiger sharks are considered a keystone apex predator; as mesopredator diversity (dolphins) and herbivores (dugongs) abundance are indirectly affected by the “seascape of risk,” as well as by direct predation [20]. 15 years of data collection in Shark Bay has supported the idea that the non-predatory effects of top apex consumers (predator keystones), play a pivotal role in influencing ecosystems [10]. Thus shark declines are affecting mesopredator numbers and behaviour, with unknown consequences on the rest of the aquatic communities [44].

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Clearly, hunting apex predators can have detrimental, aggregating effects on lower trophic levels, both directly (via predation) or indirectly (through the landscape/seascape of fear concept). Equally, the idea that keystone’s play a role within and across communities [27], was seen with the decline of sea otters in the Aleutian archipelago populations due to increased predation by Orca [42]. The overexploitation of fish stocks in these waters in turn reduced populations of pinniped that fed on them [11]. This altered the orcas behaviour which began targeting otters as an alternative food source. Kelp forests once again declined as urchins were free of predation. This is known as the exploitation ecosystems hypothesis, where the food-chain length determines the level of influence and control top-down or bottom-up systems have in the primary productivity of ecosystems [10, 11].

Great White Shark

Future: Management, mitigation and reintroduction

Problems

In terms of keystone species, the challenges of managing and mitigating their decline arise due to the complexity and interconnectedness between the many species they affect within ecological communities [5]. For example, managing the declines of seed dispersers is hard due to the large spatial ranges of their territories and difficulty in quantifying dispersal rates [23]. The extent to which urban-adapted keystones will affect the rest of the community depends on their ability exhibit behavioural plasticity and adapt, which varies between species and landscape scale [35].

The threat of climate change is also difficult to predict, thus is hard to prevent plant-pollinator loss in the future as phenological shifts continue at different rates [4]. Similarly, the uncertainty surrounding model projections of sea ice loss threatens the future survival of many Arctic species [25]. In aquatic systems, the lack of protection out of marine conservation areas and the extensive movements of keystone predators such as sharks, creates problems in managing and mitigating their decline [21, 22].

Equally, the overall concept of what constitutes a keystone species provides difficulties in management [7]. The definition can be broadly used to describe a spectrum of keystone types, which is confusing and problematic for conservation policy [7]. With an increasing number of species being given ‘keystone status,’ the lack of consistency in defining them more scientifically is rapidly becoming a challenge in itself [27].

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Identification of which trophic direction is most influential in affecting levels of biodiversity within communities is controversial [10]. Often, it is dependent upon the ecosystem as well as the keystone specie. Some argue that primary production controls ecosystems bottom-up [18]. Others believe predatory top-down control is more influential, and is currently gaining more support due to the mounting evidence that global predator declines have significant impacts on communities and ecosystem processes (Figure 3, [10]). However, even if top-down systems were recognisably more important in structuring ecosystems, it is hard to determine the most prevalent impact predators have in influencing interactions within food webs- directly (through predation/lethal) or indirectly (risk effects/non-lethal [34]).

Figure 3: Indirect impacts of apex predators on different ecosystem function and processes (Source: Estes et al [10]).

Indeed, this is the case with sharks, where the importance of risk effects might be underestimated [26]. In terrestrial ecosystems, the ‘landscape of fear’ as well as direct predation by wolves is being taken into account in studies of natural systems, (eg: Białowieża Forest, Poland) in order to consider the nonlethal effects on herbivores [32]. Proposals by Manning et al., [34] suggest that controlled experiments in the Scottish highlands would provide much needed data and viable evidence for their reintroduction. However, public opinion is often divided in terms of reintroductions [37], and the funding and costs of trial experimentation are deemed wasteful [32].

The nature of predicting ecosystem response with the removal of a keystone is also very difficult when taken from a stable environment- where prior knowledge of the response in unknown [36]. Only a few studies have examples of networks that are partially mapped [5], and the substantial lack of data on a range of ecosystems makes management difficult [36]. Much earlier research does not indicate the strength of each trophic link, thus it is difficult to compare to the current consistent and empirically accurate data. Even when disrupted, other factors such as intraspecific competition can alter the response, and may take many years for the effects to propagate in the ecosystem [10]. Current strategies by the US Endangered Species Act fail to incorporate this [41].

Possible solutions?

It is vital that scientists are able to quantitatively asses the relative contribution of each proposed keystone [36]. Only then can policy makers implement management strategies that target and focus on protecting species that have the most important functional role- rather than the rarest specie [27]. We must also therefore demonstrate their functional importance before policy-makers act on the impetus of the analogical term of a keystone [7]. Of equal importance is understanding the connectivity of networks as well as attempting to mitigate the threats facing keystone apex predators. The geographic spatial scales at which natural or previously manipulated experimental removal experiments varies enormously, thus must also be considered in future reintroductions and management plans [39].

panda

As already established, complex ecological concepts are hard to manage as many factors feed into the function, stability and persistence of food webs; including biotic and abiotic factors [10]. It is clear how important abiotic interactions greatly influence ecosystems and community structure and function, and must be considered if we are to manage and mitigate the effects of current and future climate change [19]. Therefore, as the fifth assessment by the IPCC suggests, anthropogenic climate change policy should focus on mitigation by following resilience pathways and realising adaption measures towards a more sustainable future [24]. If we are to reduce the number of extinctions, policy must also address the source of the problem; fossil fuel consumption, to mitigate the severe effects it could have on vulnerable keystones and their habitat [24].

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Other concepts such as network theory have helped explain how the systematic targeting of particular keystone individuals is far more destructive than random removal [36]. Therefore fisheries must implement this into their harvesting methods and reduce their impact on sharks by implementing annual moratoriums to prevent over harvesting. This will require international cooperation to account for the spatial movements of these keystone predators [44].

Conclusion

The threats facing keystone species may arguably have the greatest impact upon ecosystem function and stability globally [10]. Keystone predators in particular play an important role as their loss is a cause of many secondary extinctions [21]. The complexity of these networks cannot be undermined, and scientists must now be able to predict and further assess why certain keystone species are more robust or more at risk from collapsing early on than others. This will determine which species will have the greatest impact upon the stability and function of communities [46]. Additionally, completion of fully described networks will need to be of a multidisciplinary manner, in order to expand upon the current knowledge of these systems. Mitigating the threats as well as assessing the success of keystone reintroductions in influence levels of biodiversity is also key [44]. The reduction of harmful human activities is also necessary in order to prevent future extinctions and declines in biodiversity [24]. Ultimately, the solutions to the challenges facing keystones and ecosystem function are not simple. However, further knowledge of how these systems work and the implementation of efficacious management strategies will lead more efficient restoration and protection.

cameleon Animals

 

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