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Loss of Apex Predators

News & Views

Loss of Apex Predators in Dual-Apex Systems

By Tania Esteban, Samuel Ross, Jessica Rushall, & Louise Shuttleworth

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Apex predators are in global decline. The description of possible complex interactions between apices in dual-apex systems calls for further research.

Apex predators occupy the highest trophic level of an ecosystem, thus do not have natural predators themselves. They are capable of affecting ecosystem functioning through consumer-control and strong trophic interactions. There are currently unknown interactions between apex predators and mega-herbivores in systems where both are present. Because of this, the loss of apex predators from a ‘dual-apex system’ could affect communities in a highly complex manner. The decline of apex predators should be considered in systems with both mega-herbivores and apex predators. Tambling et al., (2013) explored this concept in an African ecosystem where lions (apex predators) and elephants (mega-herbivores) co-exist. In this article we discuss the potential effects of apex predator loss in this ecosystem.

trophic cascasde

Mega-herbivores perform important functional roles in ecosystems. For example, elephants alter plant community architecture through trampling and overgrazing1. Direct aggressive interactions between elephants and other animal species also occur in these systems2, highlighting the key role of mega-herbivores in influencing species dynamics. Elephants also have indirect impacts on other herbivores through exploitation competition over resources, and depending  on the  system,  are sometimes able to outcompete smaller herbivores1.

meg herbs 2 meg herbs 1

Figure 1. Weighted trophic interactions between species in the presence of apex predators: (a) with; and (b) without mega-herbivores. Interaction strengths are depicted by line thickness.

Lions are important apex predators in African ecosystems. They exert consumer-control, through predation on small and medium/large sized ungulate species, such as duiker and kudu respectively1. Like elephants, lions are classed as a flagship species because they are globally renowned, captivating, and of conservation concern. Lions are classed as vulnerable3, and are in decline because of hunting and persecution; diseases including CDV; and habitat loss due to agriculture and urbanisation4. If lion numbers continue to fall, large detrimental impacts on these ecosystems might be seen.

In multiple apex systems, interactions between apices are likely. Despite a lack of literature on the topic, there are potentially undescribed interactions between species occupying these apex roles.

Apex predators are likely to interact indirectly with other ‘apex consumers’ including mega-herbivores5. One of these indirect interactions can be facilitation by one apex on another; for example facilitation of predatory success of apex predators by mega-herbivores through environmental modification1. Another of these indirect interactions between apices would be the loss of one apex from the system. It is widely recognised that the loss of consumer-control has widespread effects, with the impacts of this loss propagating through the ecosystem. On a larger scale, trophic downgrading is a global threat, as systems are driven towards simplicity when consumer-control by apex predators is lost5.

In an African thicket ecosystem, Tambling et al., (2013) studied the interaction between lions (apex predators) and elephants (mega-herbivores). In this system elephants facilitate predatory success of lions through overgrazing and trampling of dense thicket vegetation. This allows access into the dense vegetation, which lions utilize because they are sit-and-wait predators. Lions will preferentially select for foraging habitats that maximise cover, over abundance or value of prey6. Therefore, modification by elephants facilitates an increase in encounter rates between lions and their smaller ungulate prey, as these  species predominantly inhabit this thicket vegetation1. In the absence of mega-herbivore facilitation, lions predominantly feed on larger prey species, as they do not have access into the dense thicket vegetation in which the smaller species reside [see figure 1].

As briefly discussed by Tambling et al., (2013), loss of apex predators in these systems could lead to multi-directional trophic cascades. Compared to unidirectional trophic cascades, impacts of predator loss can radiate through the system in a nonlinear manner. For example, apex loss could propagate down through trophic levels and ‘rebound’ back up towards the second apex (mega-herbivore) through changes in populations of smaller herbivores.

In a classic trophic cascade, apex predator loss results in increases in herbivore populations7. The extent of population responses to predatory release depends on ecosystem structure. In the African thicket ecosystem where mega-herbivores facilitate lion predatory success on small ungulates, if lions were lost from this system, the resulting population changes of small herbivores would be greater than in the absence of facilitation by elephants. Where elephants are not present, lions mostly cannot access small prey species that frequent dense thicket vegetation so they predominantly prey on larger ungulate species1, resulting in greater proportional population increases in larger ungulates if predatory release were to occur.

Following the exploitation ecosystem hypothesis, if consumer-control is lost, systems are limited purely by primary productivity so the extent of primary production determines trophic complexity8. If lions were lost from a dual-apex system, the ‘second apex’ would likely be affected, as mega-herbivores would face increased competition due to predatory release of other herbivores [See Fig. 2a]. Systems that support mega-herbivores face increased herbivory initially, so when apex predators in these ecosystems are lost, mega-herbivore populations are at greatest risk of collapse due to competitive exclusion of these species with low rates of secondary production9.

Although Tambling et al. (2013) studied facilitation in dual-apex systems, as far as we are aware there is no current research into the effects of apex predator loss in these ecosystems. The African thicket ecosystem should be used as a model for future studies into dual-apex interactions, as exploration of connections in this novel system was valuable. As briefly  outlined, complex multi-directional trophic cascades have not been widely recognised and described. If we are to gain valuable insight into the impacts of apex predator loss, we must research this area further, in different dual-apex systems, as currently little is known about the consequences of apex predator declines. Equally, the role of consumer control in structuring ecosystems is not widely recognised5. This further highlights the need to consider the effects of apex predator loss in ecosystems globally, and the importance of preserving all types of apex consumers in an increasingly downgraded world.

References

  1. Tambling CJ et al. (2013) Basic and Applied Ecology 14, 694-701.
  2. Slotow R, & van Dyk G. (2001) Koedoe 44, 85-94.
  3. Bauer H et al. (2012) Panthera leo: The IUCN Red List of Threatened Species. (available at www.iucnredlist.org). Updated 2014 (Accessed 01 December 2014).
  4. Snyman A et al. (2014) Oryx, 1-7.
  5. Estes JA et al. (2011) Science 333, 301-306.
  6. Hopcraft JGC et al. (2005) Journal of Animal Ecology 74, 559–566
  7. Pace ML et al. (1999) Trends in ecology & evolution 14, 483-488.Oksanen L, & Oksanen T. (2000) The American Naturalist 155, 703-723
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Demystifying Dementia

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This event was all about raising awareness about the devastating disease- Dementia. I really enjoyed communicating this fascinating but equally important scientific topic to a diverse audience, ranging from 4-90+. Science communication is becoming ever more so a prevalent skill for upcoming scientists who wish to elucidate their research and the work of others to an audience who have not been fortunate enough to conduct the research themselves or learn from those that have. Dementia is affecting older people every year as well as younger people (it was previously thought that 17,000 young adults had dementia, this was an underestimate and it has since been found that 40,000 have the Alzheimer’s disease). Dementia costs the NHS £26.3bn overall, and the government is considering imposing care tax to pay for the shortfall.

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This, I believe, is an injustice to the victims of a disease where no definitive cause has being established. It is wrong to enable health free care to patients with heart conditions for those who have led an unhealthy lifestyle, and deny the right of the elderly who have paid into the systems for many decades and led otherwise, healthy lives. I talked about the symptoms, causes, diagnosis and possible treatments successfully and reassuringly to the audiences, as well attempt inspire younger public members to keep fit and lead an active life… some inparticular were more eager than others! One girl would not stop having a go on the exercise bikes! I am a passionate sportswoman and really enjoy having a healthy lifestyle, and I wanted to share my experience with others and encourage them to live a fitter and more exhilarating life through exercise.

Brain

Before I go on, here are some quick facts about what Dementia actually is:

# 1 What is Dementia?

It is a set of symptoms as a result of several diseases such as Alzheimer’s, Lewey Bodies, Fronto-temporal and Vascular dementia which cause the typical set of symptoms such as:

-Loss of coordination

-Difficulty of remembering times during the day, appointments

-Difficulty with speech, slurring words

Uncoordinated movements

Confusion, fear and anxiety

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Depending on which disease has caused the specific set of symptoms, they can vary enormously. This is why it is VITAL to go to your GP to check this out. They will run a thorough set of checks: blood tests (to see if there is another cause, for example side effects of medication), CAT and MRI scans of the brain, physiologist will perform mental tests to see how the brain copes as well as other in-depth memory tests. There is plenty of info on their website: http://www.alzheimers.org.uk/

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The event was very rewarding and I believe the general public also felt that they had a great experience. The first day on the Saturday I was a little nervous, however as people began asking questions and showed genuine interest I really enjoyed myself, and Sunday I had “rehearsed” the talks. The range of different ages of general public members was large and certainly more interesting. What did work very well was the How brains work stand, with the rat/mouse/snail brains and neurone pipe cleaners, the children were simply enthralled and fascinated by these real life organs, and the younger children were delighted to have something soft and colourful to make and then take home. The adults, to my surprise, asked quite a lot of questions with regards to the symptoms and diagnosis of dementia on this table, which I had prepared for with the excellent notes provided on the Alzheimer’s society website.

The How Science works stall with the chromatography and gel electrophoresis was a bit hit, with the widest range of ages all participating on both activities. We had so many people at one point that we ran out of chromatography paper! We got the children to try a fusion of different patterns and colours from the chromatography which they loved, and the creating of a role play scientist really got them engaging with us and participating in the pipetting of the food colouring in the wells. The thought of dressing up as a scientist for many was the most fun out of the activities on the table, and parents enjoyed taking photographs of them.

Chromatograhy with salt

The multi-coloured chromatography designs were dried and stuck into their activity books to keep and show to their teachers; these booklets were most definitely popular and a good motive for the children to keep going around and get involved in all the activities. It was extremely rewarding to see the delight on their faces as they saw what they had created. When praising them for their work they were more willing to try out new activities and ask questions.

What didn’t work as well was the larger neurone which involved more children, it wasn’t as entertaining for them, and they felt slightly more embarrassed than doing the pipe neurones. I think in the future face painting would be a very good way to engage children and keep parents at the event for longer. BBC One show presenter Marty Jopson was also there with his children and wife, so that was a surprise! His children clearly had his love and passion for science, and were particularly good at the exercise bikes and blood pressure monitor testing.

marty_jopson_rdax_800x532

Having to tailor information for particular age group was initially challenging, but then as I gained more practice at it, I felt more confident in toning town the level of complexity for younger groups, then increasing it again for adults, and more so for academics. I certainly felt more confident in communicating with a broad range of people as well as approach people rather than wait and hold back for people to communicate with you. I never thought that I would be able to relate to children in a scientific manner which I did, and I truthfully felt rewarded when children were inspired and excited by the science we were explaining to them. I had to remember how to use my artistic side, having created a staggering 36 neurones! I really enjoyed myself and look forward to participating in some more, possible even consider leading an event now that I feel more confident.

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Having read up on Dementia and the diseases that cause it has giving me a new found interest in the science behind it, the proteins that cause such damage- talking to the PhD volunteers was interesting and I believe I have learnt a lot about the disease. It has inspired me to go on to do a 5k run for the Alzheimer’s society, and help those in need of care- it really is a good cause and I hope I can do my bit.

Here is the link to the Leeds University web page- the team of researchers are doing an AMZING job of trying to combat this deadly disease: http://www.stem.leeds.ac.uk/ai1ec_event/healthy-brains-leeds-demystifying-dementia/?instance_id=

River filming and solitary bees

Took the camera down to get some river shots to add to the doc which was rather refreshing. On my way down the road I also thought I could include the bones that the eagles incessantly drop and eat the marrow from the scattered remnants of old and sick goats that died on their last “paseo” across the vast Mijas mountain ranges.

bones on roof from eagle

I have never found out which are the ones that do such a thing, what a shot that would make! Many raptors do this: gaining access to the nutritious marrow which is often the only scraps left from an otherwise arid landscape. Also some scenes of a rather impressive algarroba tree.

Algarrobo tree

By the time I got the river, it was still rather stifling hot at 6pm, so I rapped up with a couple of river scenes and did a piece to camera on solitary bees. Originally I was going to one on ants, but seeing that they moved around at an impossible speed, I decided an over-worked bee would be slightly easier but no less interesting. The poor insect clearly had seen better days, it had literally worked itself into this state, as a solitary worker bee.

Me presenting bee

Most people have the perception that these ancient insects are primarily social, however, over 90% are solitary bees! The females will find crevices and cracks to construct underground nests, where they will lay their eggs. The food provided to the offspring in the form of pollen and nectar (the only diet of the bee’s having evolved down a different dietary route from their carnivorous ancestors, wasps). This food is gathered, but after no care is given after laying the eggs- unlike in the social colonies. The three social groups include bumble bees, honey bees and the stingless bees. They all exhibit eusocial behaviour, that is, they show the highest level of organization of animal sociality,  defined by cooperative brood care (including brood care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labour into reproductive and non-reproductive groups. The division of labour creates specialized behavioural groups within an animal society which are sometimes called castes . Eusociality is distinguished from all other social systems because individuals of at least one caste usually lose the ability to perform at least one behaviour characteristic of individuals in another caste.

bee 2

I noticed that the goat farmer had marked out all of his land with a pathetic little fence, and in doing so, taking a bit of our own land in the process. He was growing some rather withered looking melons and other unidentifiable crops. What a waste of land!

goat farmers farm, melon shot

He had entirely destroyed the back of the river, along with it all the vital berry bushes and habitat for nesting birds such as the stunning Nightingale and ground nesting birds such as they grey partridge. I actually heard a partridge on my way back up, no luck in seeing it though. All in all, quite a fun experience and got some good footage to edit, it’s a wrap!