Hunting - A Bear Necessity?

A nasty note on which to start the new year, but the US Fish and Wildlife Service (FWS) has announced that their intend to remove protection from Yellowstone's grizzly bear population in the coming year. As someone who has had a grizzly bear themed calender for the last two years, my immediate reaction to this is one of shock and disgust. For a moment, however I will attempt to step back from my bear loving self and take a look at the reasons behind this decision.

Adorable animal which should clearly not be hunted; Source.

For the past 40 years, the bears of Yellowstone have been protected by hunting and have enjoyed population increases and range expansion under this protection from the Endangered Species Act (ESA). This protection was not undue, the grizzly population suffered huge losses from excessive hunting during the 1900s which earned them a place on the IUCN red list. The recovery of their population, however, has put pressure of the US FWS to revoke their special status, from state officials. The proposed new system would involve handing over the management of bear population to state level, after the delisting would remove federal protection. The agreement places no limit on the hunting of bears outside of the central Yellowstone management area, and within that splits the bears between the three states which share the region - Wyoming, Montana and Idaho. There are some loose pledges to maintain the bear population in the management area above 600, but nothing concrete except an apparent need to shoot at things.

Arguably, the new laws would promote, rather than limit the killing of bears. There are underlying societal and economic reasons why there is such animosity towards bears, and other large carnivores. Whilst states would plead that bears area threat to humans, the reasoning is more likely to do with their role as competitors for big game. However, the problems of hunting these animals also have multiple dimensions. Culturally, they hold high significance for many native people who also live in the Yellowstone management area and have not been consulted in the decision to delist bears. Ecologically, there are many issues in play. Bears are, arguably, still in a very vulnerable position in Yellowstone and are dying in disproportionate numbers each year even with the protection of the ESA. For example, climate change induced drought and invasive species have extirpated one of the bears main food sources, the cutthroat trout, as well as damaging other food sources including Whitebark pines and elk. Grizzlys have very low reproductive rates, with huge amounts of parental investment, meaning that they are very slow to react to changes in the environment and colonise new territories. This means that they will feel the pressures of climate change more than most, causing their population to suffer alongside hunting.

My personal bias aside, I feel that there is not a great case for delisting the grizzly bear from the ESA protection. There is a very real chance that hunting would lead to extirpation outside of the Yellowstone management area, where there are no limits in place. Isolating the population within Yellowstone, whilst hunting them as well, could have disastrous impacts on then stability of the population as their numbers dwindle and their genetic diversity lessens. Let me know your thoughts below, but I feel that there is no necessity behind this law change, simply a demand for blood.

Could the removal of the 'ESA Safety Net' mean extirpation for Yellowstone's grizzlys?; Source.

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.

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.

The Mystery (or not) of the Megafauna

Between 50,000 - 10,000 years ago over 90 genera and many hundreds of species of megafauna went extinct in what have become known as the Late Quaternary Megafaunal extinctions. Megafauna, or for our purposes large mammals weighing over 44 kg, lived around the globe on all continents except Antarctica but today they persist only in Africa. The causes for this dramatic decline in species over a relatively short window of time is a contentious topic which has two polar ends: humans and climate. Some papers argue that humans were the overriding factor through a variety of impacts such as hunting and habitat destruction, whilst others maintain that climate change was the real killer.

Some of the Quaternary Megafauna; Source.

The megafauna were more vulnerable to extinction than other animals, which is in part why they suffered such extreme losses, whether they be from humans or climate. In general, animals of a large size are more vulnerable to extinctions due to larger ranges and lower population densities. Johnson argued, however, that is was not size but a slow life history (slow reproductive rates and few young) that made the megafauna more susceptible to extinctions. Due to the fact that they have long lives (and therefore later sexual maturity) and relatively few young, they are more vulnerable to sudden changes in climate and habitat because it takes longer for generations to pass and therefore longer for the species to adapt to these changes. This supports climate causes over human, as hunting hypotheses focus on body-size. Johnson also found that those alpine, arboreal and nocturnal species with lower reproductive rates experienced less extinctions, likely due to their reduced exposure to humans but there is no clear link to climate.

Barnosky et al. conducted a review of the evidence from a variety of fields. They found that in some areas, such as Eurasia and North America there was strong evidence that humans contributed to the extinctions but also that pronounced climate change had a significant role. In Australia, humans were almost exclusively responsible for the loss of 21 genera whilst there was scarce evidence for the influence of climate. In other areas of the world, South America and Africa, there was not sufficient evidence to make a judgement on the causes of the extinctions, despite the fact that South America experienced the greatest species loss of any continent. In Africa, there is a very low number of genera lost in comparison to other continents. Why? This is yet another unanswered question but we think it is due to coevolution of humans alongside the megafauna.

Assessment of causes of extinction on each continent; Source.

There are various hypotheses for human caused extinctions, but I will briefly discuss the most common ideas. 

1. Blitzkrieg

Whilst this is now considered somewhat outdated by most scientists, one of the first ideas about the loss of megafauna was that humans had hunted them to extinction at such a rapid rate that their populations did not have a chance to recover. First proposed by Martin, the hypothesis assumes that as the animals had not encountered humans before, they would naively not be afraid of them and therefore easily hunted. Martin sought to provide explanation for the fact that there were so few archaeological sites containing extinct megafaunal remains, as the hypothesis put the extinctions within the space of 500-1000 years so interactions between humans and extinct species would have been brief. There are, however, a number of issues with this hypothesis. There is a severe lack of archaeological sites where large mammals are associated with stone tools and Barnosky et al state that when the entire breadth of climatic and archaeological evidence is considered, that blitzkrieg scenarios can be firmly rejected in western Europe, Siberia, Alaska, and probably Australia and central North America. Additionally, Wroe et al. among others argued that prey naivete would not have been sufficient for blitzkreig, as this is really not how animals work - prey quickly learn to flee from new predators. Whilst we know that hunting and predation by humans did have an impact on populations, and of certain species in particular, we know fairly certainly that it was not a blitzkrieg.

2.Sitzkrieg 

The wittily named Sitzkrieg hypothesis refers to the slower, sometimes indirect impacts humans would have had on megafaunal populations other than directly hunting them. This includes habitat loss and fragmentation, use of fire, and the introduction of foreign species and diseases. This has proven difficult to quantify as, for example, we cannot pinpoint whether charcoal comes from human or natural fire events and it is also difficult to know the extent of habitat loss. We have seen in island communities that 'sitzkrieg' style events have caused extinctions through multiple effects and synergy with hunting. For example, black rats as a human introduced species have caused extirpations in island communities, but this has not been replicated on mainland. Some suggest a hyper-disease hypothesis in which extinction is a result of hyper-virulent diseases to which the native species have no resistance. Again, there is a lack of evidence to support this - we do not actually know of any such extremely lethal cross species pathogens, for example. In their review, Koch and Barnosky find that none of the indirect sitzkrieg models make strong predictions regarding the megafaunal extinctions. Of all, the factors, habitat alteration seems the most likely culprit but it is unlikely any sitzkrieg parameters were dominant causes of the extinctions.

Hyper-disease, plausible or silly?; Source.

As for environmental hypotheses, climate change is the prevailing theory but there are also some other weird ideas out there.

1. Climate change

Throughout the last 50kyrs, there has been a lot of fluctuation between warm and cold events in the climate, known as Dansgaard–Oeschger (D-O) events (rapid warming events) and Heinrich events (cold events).  These events are likely to have caused abrupt shifts in temperature and precipitation which would destabilise habitats and species ranges. In a recent paper, Cooper et al identified that many extinctions seem to coincide with D-O events, shown in the graph below. Additionally, Gill et al found that Sporormiella (a dung fungus associated with large herbivores) declines in correlation with D-O events and overall gradually throughout the period, contrary to the aforementioned blitzkrieg ideas. The other trend we see is a gradual warming from the last glacial maximum (26.5kya) to the Holocene (11 kya), after which temperatures remain relatively stable. This warming would have caused major ecological changes, in particular the reduction of tundra biome and taiga forests reaching further north. Some species, such as mammoths, were not adapted to these warmer, wetter forests and would have suffered from a decreased range and were likely unable to keep up with a shifting habitat due to their large size and slow reproductive cycles.

Light grey bars represent interstadial warming events and have a marked association with extinctions; Source

2. A comet?

The Younger Dryas impact hypothesis suggests that a barrage of meteorites hit the ice sheet in North America and created instability and caused the onset of the Younger Dryas. However, this is widely discredited as we have evidence (such as Gill's sporormiella) that tells us the megafaunal extinctions were not clustered around or after 12.9kya when the impact occurred. The event itself is disputed due to lack of typical bolide indicators found in sediments from that time. So, not really anything to write home about, but just letting you know what's out there. ;)

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In summary, as shown in the original graph by Barnosky et al, the evidence points towards a mix of human impacts with a background of climatic events as the drivers of megafaunal extinctions across the Northern Hemisphere Whilst the jury is still out for most of the Southern Hemisphere, Australian extinctions appear to be very closely related to human impacts, with little climatic correlation. We have a good understanding of what happened to many of these genera, as shown by the number of green circles representing 'robust evidence' in Barnosky's graph, but there is still room for improvement, particularly for understanding what happened in South America and Africa. It would be interesting to hear your opinions on all this, particularly if you disagree with anything I've said! As always, questions and debate and welcomed in the comments section.