Nocturnal Pollinators: A forgotten ecology?

In the post below I wanted to share what I have been working on in my independent study project. The project was about trying to establish a baseline for the diversity and importance of nocturnal pollinators, as they are a hugely under-researched group. Much of the focus of pollination research and media representation in recent years has been firmly on bees, and to a lesser extent butterflies, but the nocturnal component of the system remains unknown to many. I'll be giving a brief summary of the answers I found to my main research questions, and then talking about the relevance of this work in the context of this blog. I hope you find it as interesting as I did and, as always, please let me know if you have any questions in the comments!

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In the same train of thought as my earlier soil biota post, I feel that nocturnal pollination is another forgotten ecology - something critically important to both the ecosystem itself and to provision of ecosystem services but unappreciated as it isn't something we often see. The diversity of nocturnal pollinators and their importance within ecosystems are two questions to which current research does not provide a simple answer. Little is known about the scale and importance of nocturnal pollination services, largely due to the impracticalities of studying pollination in the dark. However, with the documented decline of known nocturnal pollinators throughout Europe and other continents (in particular, moths and bats), it is crucial that we reach a better understanding of their role in respective ecosystems. As some put it, we remain rather ‘in the dark’ about what happens after dusk.

Manduca sexta feeding from a Datura flower; Source. 

How many nocturnal pollinators are there and which taxonomic groups are they in?

Any number I gave you would be wildly innacurate. We can try to make estimations based on those species which have been observed, but a recurring issue throughout the research is the impracticality of observing things at night. Also there are taxonomic issues, particularly for invertebrates as I have discussed in previous posts. We don’t know what percentage of species we have described and many families, such as the Noctuidae moth family, are paraphyletic and contain genera not robustly assigned to subfamilies.

As for the taxonomic groups the pollinators belong to...

Lepidoptera: We know of 21 families of moths involved in nocturnal pollination. but from these some of the most important are the Noctuidae and Geometridae families which land on the flowers the same was as butterflies do but also the Sphingidae or 'hawk moths' which hover and reach the nectar with their extremely long tongues. Moths and the other insects I will discuss typically pick up pollen on their legs and wings when they visit flowers by accident and deposit it on subsequent floral visits. A few species of moth, however, are the only known insects to do this purposefully.

Hymenoptera: The family containing bees, wasps and ants. Bees are commonly thought of as diurnal pollinators but there are nocturnal bees which play an important role in desert environments. Wasps and ants are not well studied as pollinators, but we know that some species are involved in nocturnal pollination.

Coleoptera: Beetles are one of the most neglected groups in literature despite being among the first animals involved in pollination. There are several families of small beetles which are fairly well studied but we also know that large beetles, particularly scarabs, act as pollinators. Most beetle pollination is found in tropics and linked with commercially important palm trees.

Diptera: We know that flies are important pollinators and often considered second only to bees, but again they are neglected in a nocturnal context. They are particularly important in regions where bees aren't as capable, such as high altitude areas and alpine environments. The Syrphid family is considered most important among diurnal pollinators and likely there are members of this which act as nocturnal pollinators as well. Mosquitoes are actually important nocturnal pollinators, and are well studied in desert environments.

A cross section of  a cactus flower, showing how the bat pollinates it; Source.

Chiroptera: Although well known as nocturnal mammals, it is not often known that bats act as crucial pollinators. Over 500 plant species, including many tropical fruits, rely on bats. Similar to hawk moths, they hover in front of the flower, and stick their head and long tongues into the flower to reach the nectar reward – their heads get covered in pollen and they look very cute but are then effective vectors to carry this pollen to the next plant they visit.

Non-Flying Mammals: There are also mammals other than bats involved. Mostly within marsupial, rodent and primate families, these mammals make big contributions to pollination in Australia and South Africa. These nectarivorous mammals are very cute as well, with obvious nocturnal adaptations in terms of big eyes and ears. Similarly to bats, pollen gets stuck in their fur and they transfer it between flowers they feed on.

Squamata: : Lizards! There are 3 known nocturnal pollinators in this group, and all of them are geckos. Nectivory is quite well established among geckos so there is a huge potential for nocturnal that may have been missed. Research also suggests that nocturnality is ancestral state for geckos, so this further hints that these guys could be important nocturnal pollinators.

How effective are nocturnal pollinators in comparison to diurnal?

This graph is from data I collected and shows the number of studies which considered a certain pollinator more or less effective than the diurnal counterparts. The data was sorted into three categories: more effective, less effective and those which were unclear or considered equal. There isn't a straightforward answer – there is a fairly even spread between the three columns, and no one category is significantly larger than the other two. There is a potential for bats to be strong pollinators, as they have larger amounts of effective studies, but moths are seem equal in all categories despite some papers being written about biological reasons for their effectiveness. Other groups did not yield not enough data to make any sensible inferences, again highlighting bias issues within nocturnal research. What is clear, however, is that in many instances nocturnal pollinators are highly important components of the system.

How many plants are pollinated by nocturnal pollinators? Are they commercially important?

Again, this is a very difficult question. Perhaps the most sensible approach would be to consider pollination syndromes and make the assumption that if a plant displays adaptations for nocturnal pollination then it is nocturnally pollinated. However, the validity of pollination syndromes has been in question a lot incurrent literature, and is largely seen as outdated, so perhaps this isn't best approach. Alternatively, we could make the assumption that all plants with nocturnal anthesis are nocturnally pollinated, but again we know this isn't true, as some of these plants will self pollinate. In addition, there are some plants which have nocturnal-diurnal anthesis and are pollinated by a mix of daytime and night-time pollinators, so for most of we don’t know which of these are primarily reliant on nocturnal pollinators, if at all.

There is potential for nocturnal pollinators to make significant contributions to a limited set of agricultural plants. Many essential staple food crops do not rely on biological pollination whatsoever, such as corn, wheat, and rice which are all wind pollinated and  need no insect help at all. Other staple food crops, such as bananas and plantains, are propagated from cuttings meaning that they require no pollination of any form. Where we see nocturnal pollinations evidenced is mostly in tropical fruit crops including species of mango, banana, cocoa, palm, durian, guava and agave (used to make tequila). Bats and beetles are, of all groups, the most likely to be responsible for pollinating these crops. So, next time you eat some chocolate, say thanks to the bats!

Bats making their home in palm tree, which they also pollinate; Source.

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So, we've established that this is an extremely diverse group that is likely highly important commercially and ecologically. Therefore, the threats that they are currently under should be taken seriously. Unfortunately, due to the lack of research in general about nocturnal pollinators, there is an equal lack of literature considering threats and appropriate conservation measures. Whilst there are likely many more threats than this, and indeed many we are unaware of, I'll discuss one of the main, unrecognised, threats to nocturnal pollinators.

Light pollution
Artificial lighting has become a huge component of many urban areas, and has established effects on a lot of nocturnal wildlife. Moths are famously attracted to bright lighting, and whilst we use this to our advantage when using light-trapping to survey them, there is also evidence that urban lighting is effecting moths negatively. MacGregor et al. suggested that artificial night lighting could potentially limit reproduction and make moths more vulnerable to predation. Both of these impacts are quite well established with evidential backing, but there may also be impacts of their ability to see properly. Moth population declines are likely linked to artificial lighting in some capacity, though MacGregor et al. suggest that the risk goes beyond decline, but to species loss and changes in community assemblages. Other research has linked artificial lighting to declines in bat populations and disruption to ecosystem services.

Alongside other threats such as habitat loss, global warming and invasive species - many species of nocturnal pollinator, both in the UK and around the world are at risk. In the tropics, where bats and beetles provide crucial pollination services, the impacts deforestation and climate change have been felt severely and I don't doubt we will have already seen extirpations of pollinating species. It is an unfortunate situation where a combination of under-researched fields meet at a crossroads and we are probably losing pollinators before we have identified them, let alone studied their importance.

Moths below a streetlight; Source.

Merry Christmas from the "Santa Spider"

Merry Christmas to all my readers! I hope you're all enjoying a good festive break from work, university and life. Whilst I'm sure you all have better things to do today than read my blog, I thought I would bring some ecology in to your day if you're up to it! The spider below is colloquially known as the ladybird spider or 'Father Christmas' spider, which as you can probably guess, is due to the bright red, white and black markings found on the males. It's one of the UK's rarest and smallest spiders and suffered from habitat degradation throughout the 20th Century.

Eresus sandaliatus, apparently trying to sniff out a female with organs on his legs; Source.

The spider is somewhat of a conservation "Christmas miracle" and has been brought back from the brink of extirpation in the UK to a now thriving population. The spider went from an estimated 50 individuals remaining in Britain in 1993 to well over 600 in 2000. The spider makes its home in heathland, which is one of the UKs most threatened habitats, and over 90% of it has been lost to development and agriculture since 1800. In Dorset, there has been concerted conservation efforts to restore the spider populations as well as protect heathland habitats. At one site there were only 7 spiders left, but there are now thriving and have been released from this site into other areas, where they have successfully colonised. Workers from the RSPB used plastic water battles filled with moss and heather to create houses for the spiders where they could breed safely.

A cute and inspiring conservation story - I try not to be too pessimistic on this blog!

 Merry Christmas!

Tiny spider is tiny; Source.

Plastic water bottle houses, Source.

De-Extinction: Return of the Endlings?

This blog has looked at the extinction and extirpation of many species and admittedly, has been fairly pessimistic. However, it has yet to consider the growing phenomenon of 'de-extinction', perhaps there is room for a little optimism? Is this a realistic approach to conservation or is it a load of Jurassic Park wannabe nonsense? The idea based on using preserved or "ancient" DNA from several individuals of an extinct species and creating clones of each of them, we would be able to create a new and viable population of that species. There are cryo-zoos, such as the one in San Diego, which store frozen DNA of extinct species with the potential to form these clones. Much of the attention given to, and work within, de-extinction focuses on this cloning aspect, but other researchers have attempted to work through selectively back breeding a species from its genetically similar living descendants.

De-extinction efforts have already been made for many species that we have seen recent endlings of, such as the passenger pigeon, the Pyrenean ibex and the Tasmanian tiger, whereas some scientists are working on much older animals such as the woolly mammoth. However, 60,000 years is effectively the age limit for use of DNA, so dinosaurs won't be happening any time soon. The first de-extinction in history was the Pyrenean ibex, which was done in 2009 by creating a clone egg using the DNA of Celia, the (formerly) last ibex, which was taken shortly before she died in 2000. Unfortunately, the ibex was short lived and died within 10 minutes but scientists are planning to reattempt when cloning techniques have improved. This attempt, in itself, was an improvement on previous attempts in 2003 which had failed to produce an egg capable of surviving the full gestation period. Significant progress has also been made for the passenger pigeon, where DNA has been preserved in museum specimens. Unfortunately the DNA of these specimens is contaminated and fragmented due to the way they have been preserved and kept, as oppose to the ibex DNA which was stored in liquid nitrogen. However, it is still possible to reconstruct the genome by synthetic hybridisation of the DNA fragments with the genome of its closest living relative, the band tailed pigeon, which scientists are currently working on. This would then be used to create cells which contain passenger pigeon genes, which would then be injected into band-pigeon embryo with the goal to create a band pigeon which lays passenger pigeon eggs and acts a surrogate parent for it.

National Geographic cover of de-extinction issue; Source.

Since 2013, a team of scientists from South Korea and Russia have been working on the de-extinction of woolly mammoths.  There have been difficulties as although mammoths have been found well preserved, their DNA has not been intact enough to produce viable embryos for a clone based de-extinction. Alternatively, a second method has been investigated which involves the artificial insemination of elephant eggs with preserved woolly mammoth sperm. The elephant-mammoth hybrid offspring would be able to be cross-bred over several generations to produce near pure mammoths. Again, this has been unsuccessfully due to mammal sperm cells lose their potency after over 15 years in freezing. The major problem has been finding usable DNA, blood recovered from the 2013 carcass provides an apparently good chance of successful cloning - we will have to wait and see. Others are pursuing different routes to restoring the mammoth, Harvard geneticists are working on migrating components of the mammoth genome into the Asian elephant genome in order to create viable hybrids. Adrian Lister, a renowned mammoth expert, highlighted that there is a lack of suitable habitat remaining for any resurrected mammoths and that, as highly social animals, they would suffer from existing in very small numbers. However, a Pleistocene rewilding experiment known as 'Pleistocene Park' (not joking), could provide refuge for the mammoths and would also benefit from the grazing herd behaviours in recreation of steppe. Interestingly, Pleistocene Park also aims to prove that it was not climate change but over-hunting and other human interferences that lead to the disappearances of these grasslands and associated species during the Pleistocene. This could be a exciting new evidence in the debate surrounding the Pleistocene megafaunal extinctions.

Pleistocene Park in Siberia; Source.

As mentioned earlier, selective back-breeding from the closest living relatives of animals is another option for potential de-extinctions. This is being done for aurochs in Europe, based on genetic material taken from bone and teeth fragements. The last European aurochs were lost in 1627 after a long history of over-hunting and exploitation, but their descendants (most modern cattle breeds) are abundant throughout Europe. The genetic material provides a goal, so that cattle can be bred to try and reach as close to the original aurochs as possible, both phenotypically and genotypically. Early attempts resulted in the created of a new breed, Heck cattle, which are at best vague-lookalikes. Currently there are two projects, the TaurOs Project and the Uruz Project, which are competing to resurrect a true, or atleast very close to, aurochs within the next 20 years. Earlier this year, it was proposed that there could be the potential to bring back Lonesome George, or at least a genetically very similar species, by a breeding programme rather than cloning. Even if the animals themselves are clones, captive breeding, which has proved successful in many conservation efforts, will be a major part of de-extinction.

So, whilst it seems that de-extinction is scientifically possible, the bigger question is rather, should we actually be doing this? Proponents of de-extinction such as Stewart Brand would argue that we have the ability and the moral obligation to repair the damage we have done, so there is no excuse not to. Others such as Adrian Lister would say that efforts and resources should be focused on conserving currently endangered extant species. The lack of suitable habitat is also a concern for many species. I feel that whilst there is certainly value and appeal in resurrecting species and "righting our wrongs", it must be done carefully and must not detract the need for conservation efforts to currently endangered species. This is not an alternative to conservation. This is an unfortunate second best to not having lost the species in the first place.

Defaunation in Tropical Forests May Exacerbate Climate Change

When one considers the relationship between rainforest biota and climate change, thoughts tend to be that climate change has the potential to cause species loss and may present a serious threat to some of these animals. However, a paper published earlier this month turned this on its head by presenting new evidence suggesting that the loss of large mammals and birds in tropical environments through deforestation, hunting and other anthropogenic factors may actually exacerbate climate climate.

The logic behind this is placed in the role of these animals as biotic seed dispersal vectors. Large frugivorous mammals, such as the woolly spider monkey, are able to consume and consequentially disperse large seeds and fruits. Some seeds actually germinate preferentially after being passed through the digestive tract of a certain species, others such as the calvaria tree actually require to be digested to germinate at all. Large hardwood rainforest trees tend to have bigger seeds and fruits, meaning that they rely on these animals to successfully reproduce and disperse. Crucially, these trees are also those which store the most carbon from the atmosphere and are a major component of rainforest carbon sinks. Whilst they only made up 21% of trees included in the study, they are estimated to hold the majority of stored carbon in rainforests. Smaller softwood trees have their seeds dispersed by smaller mammals and birds but these experience less impact from hunting and the trees are less important carbon sinks.

How mammals and birds aid dispersal in a healthy vs unhealthy forest system; Source.

Large animals provide almost all of the seed dispersal services for hardwood rainforest trees, so play a crucial role in maintaining the rainforest carbon sink which stores 40% of the world's terrestrial carbon. Several of these animals are threatened by anthropogenic activity including deforestation, hunting and habitat loss, a brief look at the IUCN Red List will make this abundantly clear. Many of these threats are growing, for example, unsustainable hunting has increased in tropical forests in recent decades and threatens 19% of all tropical vertebrates, with larger vertebrates affected at disproportionately higher rates. Smaller vertebrates such as rodents are also impacted by defaunation of larger mammals and can become locally extinct in overhunted areas. Extirpations of large mammals in tropical forests, whilst a tragedy in itself, has clear potential to limit the ability of rainforests to act as carbon sinks. Whilst policy has mostly focused on limiting deforestation, more focus is needed on the conservation of large mammals through prevention of forest degradation and restricting hunting.  Between 7-17% of global carbon emissions could be at stake unless defaunation is prevented, which is a huge amount of CO2 to be at risk.

Look Deeper: Extinction Risks to Soil Biota

Earlier this week, we celebrated World Soil Day (4th Dec). One of the key themes in this years festivities was to highlight the need to increase research into soil ecology and underground ecosystems. In particular, to warn of the potential underground extinction risks that we have an very limited understanding of. A new collection of papers has been published in Nature as part of World Soil Day to highlight these issues among other soil related discussions. So, in accordance, I will be bringing these issues to my blog to give us all an education about soil ecology, as despite the relative neglect compared other areas of ecology, the soil and its biota are fundamental components of all terrestrial ecosystems.

In order to form conservation approaches for underground ecosystems, we need a clearer understanding of the diversity and functionality of them. We know that soils provide vital ecosystem services, particularly for agriculture, so there is clear motive for conservation action - regardless of a lack of moral motive, as concern for things small and dirty tends to be less. The extent of biodiversity below ground is hugely unknown, partially due to the impracticalities of studying these organisms due to their size and inaccessible habitat.  As shown in the graph below, taken from one of the new papers, the vast majority of what lives in the soil is under 1mm in size. What the graphs also shows, however, is the extreme abundance of these organisms - over 1kg of bacteria per meter squared is an insane amount of individuals! Aside from our poor understanding of the diversity, other challenges for understanding potential extinction risks include the lack of suitable models, the complexity and density of microhabitats within the soil and uncertainty about temporal and spatial scales. I'm not going into these here, but they are all detailed here if you're interested!

Soil biota, shown by coloured crosses, are generally very small and very abundant ; Source. 

The most important extinction risk factors for soil organisms are not dissimilar to those faced by their terrestrial counterparts. Habitat loss, a concept we are all familiar with in relation to aboveground organisms, can cause equal disruption for soil ecosystems, for example through the fragmentation of the soil surface via urbanisation. This has been shown to link to declines in abundance of nematodes and other soil biota. Equally, climate change and global warming pose a threat just as they do to terrestrial and marine biomes. Extreme drought events can cause devastation of soil based habitats, for example. Climate change is also thought to have some more complex impacts on soils which can be equated to habitat loss, due to the degree to which the soils are changed. It has been shown that the increased atmospheric CO2 concentrations lead to a reduction of nematode diversity due to the loss of pore spaces in the soil which are required by the organisms. Soil habitats are also impacted by agricultural practices, such as tilling, irrigation and fertilization which impact both soil structure and composition. It is thought that these factors drive constant habitat loss for components of the subterranean community. Although it is difficult, as mentioned above, to know the extent of these impacts, we do know that many of the susceptible species, such as earthworms and mycorrhizas, are of major functional importance to their own ecosystems and ours. There are also potential risks from invasive species, but at a microbial level more than invertebrate, which have likely been spread as a result of travel and tourism. Many of the soil biota are highly specialized in their niche, which is commonly considered to make them more vulnerable to both invasions and extinctions.

So there are considerable risk factors stacked up against soil ecosystems, much as there are against the terrestrial. There has, unfortunately, been very little conservation action in comparison. Some studies have already documented local extinctions of earthworms and various fungi due to the factors discussed above. So perhaps we should start taking some action? This, if any, is a good time to start. 2015 is the International Year of Soils, as declared by the UN General Assembly, after-all. This declaration was made with the intent to raise awareness of the life-supporting functions of soils and to promote the importance of soils in achieving a number of the new 17 Sustainable Development Goals. I hope that you've learned something about the oft-neglected but important goings on beneath our feet, and that in future you might give them a thought in conservation discussions.

Happy World Soil Day!