The peacock spiders

Within the salticid subfamily, Euophryinae, are a number of genera with complex mating rituals and males with elaborate ornamentations on their bodies that are used in the act. Of these, the genera Saitis and Maratus are characterised by an elongated leg III that is used by the males in signalling to the females as part of their mating displays. Maratus, which are endemic to Australia, have especially attractive males as they have taken this ornamentation further by having flaps or extensions on their brightly coloured abdomens which fold out during the height of the mating display. The abdomen is raised and displayed to the females (along with the raising of their leg III) in a manner similar to that of a strutting peacock. This has earned them the common name of peacock spider.

A few years ago I had the opportunity to photograph these spiders, but unfortunately I did not capture any mating displays. Recently, a paper was published on these remarkable little salticids that describes in detail their mating behaviour and has an amazing series of accompanying photographs, especially of Maratus volans. Photos of other species, such as M. pavonis, are few and far between and I was lucky to have a few of my photos used in this paper. You can download the paper here (~8.5mb).

Last week I was able to get out to try and find these spiders again, and was lucky to find them in the same area where I photographed them three years ago. This time, although I did not observe the full mating display of the male, I was at least able to capture some signalling by the males using their leg III and observe some interesting interactions. Click through to see more photos, read more information and observations on these remarkable spiders. Hopefully one day I will be able to photograph a full series of the entire mating display.

Spider guilds

When faced with seemingly random species loss as a result of disturbance, it often helps to place the focus organisms into guilds or functional groups to better understand the factors mediating their populations and how this impacts upon ecosystem function. In the case of spiders, this approach may help reveal how, and to what extent habitat structure or prey availability affects the distribution, diversity and abundance of the spider community in question. Although the terms guild and functional group are more or less used synonymously in ecological literature, they actually refer to different suites of organisms. Guilds are groups of species who share similarities in how they share or use a resource (such as food or habitat structure), whereas functional groups are concerned with the similarity in how a particular resource is processed in relation to ecosystem function (i.e. nutrient cycling). See Blondel (2003) for a review on the subject.

Why guilds? Spiders are all obligate predators of other arthropods (i.e. they all provide the same ecosystem service), but differ in their foraging methods and the way in which they utilise the environment to capture prey (e.g. active hunters vs. web builders). Hence the term guild is more applicable to spiders. Care needs to be taken, though, when defining guilds within the context of the study to ensure that the similarity in resource use will accurately reflect the changes one is measuring. Often, studies partition species a priori without utilising any quantitative methods and end up with nothing more than parallels of taxonomic groupings that have little use in making ecological comparisons.

There has been any number between 2 to 11 spider guilds purported by a number of authors, relying on differences in foraging method, spatial and temporal preferences, but also heavily drawing from taxonomic groupings. A study by Uetz et al. (1999) utilised a quantitative analysis of ecological characteristics of spider families as an alternative approach to guild classification. By looking at foraging manner, web type, microhabitat use, site tenacity and diel activity and subjecting these characteristics to a hierarchical cluster analysis, they were able to produce a dendogram (see below) that allowed guilds to be assigned on the basis of the similarity between spider family clusters. In making comparisons of spider guild composition they found that “patterns of similarity in guild composition suggest the possibility of plant habitat structure as an influence on the spider community”.

I have modified this guild classification somewhat to accommodate the different spider families found in Australia. I have also split guilds where I felt it could afford me a higher resolution when comparing habitat utilisation. Where particular spider genera differ in their primary foraging method from their representative family, I have placed them in their respective guild.

Ground runners: Corinnidae, Cycloctenidae, Dysderidae, Gnaphosidae, Lycosidae, Miturgidae, Nicodamidae, Zodariidae, Zoropsidae

Foliage runners: Clubionidae, Zoridae, Cheiracanthium

Trunk runners: Hersiliidae

Rock runners: Selenopidae, Trochanteriidae

Ambushers: Philodromidae, Pisauridae, Scytodidae, Segestriidae, Sparassidae, Thomisidae, Arkys

Stalkers: Lamponidae, Mimetidae, Oxyopidae, Salticidae

Sheet web builders: Agelenidae, Amaurobiidae, Cyatholipidae, Desidae, Hahniidae, Linyphiidae, Oecobiidae, Psechridae, Styphidiidae

Space web builders: Dictynidae, Pholcidae, Theridiidae, Cyrtophora

Horizontal orb weavers: Tetragnathidae, Uloboridae

Vertical orb weavers: Araneidae, Nephilidae

Line web builders: Miagrammopes, Ordgarius, Phoroncidia

Net casters: Deinopidae

Using guild classifications such as these should give me an insight into the differences in habitat utilisation between guilds and why, as an indirect result of the effects of salinity on riparian vegetation, there is a shift in the composition of spider guilds in my study area.

Say 2,3-Benzopyrrole!

Hokay, my poor attempt at ant humor aside, I wanted to share a recent portrait I took of a surprisingly cooperative Myrmecia worker. Now, those that are familiar with these ants will know how difficult they are to approach – they are very alert and aggressive, and do not hesitate to attack any intruder, regardless of their size. While searching for more elusive Myrmecia species, I came across many a colony of these more common and conspicuous (+20mm) bullants, but none presented themselves with any opportunity for a photograph, being too active and all. Eventually I found an individual that was in a more favorable state, and she let me get in nice and close. This particular worker, while still alert and interested in defending her colony, didn’t continuously charge at me like the others, but carefully and seemingly purposefully watched me from a nearby granite rock. Of course, it probably just came down to the fact that it was a cold Winters day and this worker had not reached optimal operating temperatures! Anyway, I managed to capture a few different ‘facial expressions’ (at close to 4:1x lifesize), but settled on the image below as my favourite. It definitely holds true to their usual behavior!

Previously, whenever I wanted to photograph these wonderful ants, I would head out late at night to some local bushland where I knew some larger colonies were. Even though this particular species does not seem to actively forage at night, there were always a few workers patrolling the nest entrance. Being much cooler though, you could quite safely approach the workers without worrying too much about being stung and get in nice and close for some portrait work. Of course, it is always a good idea to keep watch on the other workers, just in case one decides to attack. Thankfully I have never been stung while photographing these beauties. Enough talk, though – below are a couple of my favorite older portraits of these charismatic Australian ants. Enjoy.

Hi!

Many thanks to Alex and Roberto for their warm welcome to the blogging world. They both have wonderfully interesting blogs and it was very kind of them to throw some hits my way. I have especially been a fan of Alex’s ant photos for a long time, being a myrmecophile myself, so it means a lot to have him link to me.

A big myrmician hello (try to imagine the Podomyrma ant above is waving at you) to all the people who have dropped by via Myrmecos or Archetype. There isn’t much hapening on this blog yet, but hopefully it fills out nicely in the coming months. My aim is to find a nice balance between posting about ideas for my project and sharing interesting natural history moments via my photos. Also, if you yourself have an interesting blog I don’t know about or know of another that I should check out (especially anything about spiders), please let me know. I am quite new to the blogging circles so am still finding my way around. Although, checking out everyones blogroll helps heaps in that department.

Happy adventuring.

Myrmecia: not as invincible as I thought

I had always thought of Myrmecia ants as the kings queens of the jungle undergrowth. They are highly aggressive ants, with extremely good vision, a powerful pair of mandibles and a potent sting at their disposal. It is hard to imagine any other predatory arthropod taking one on and coming away unscathed. Of course, in the ant world numbers are king – you can see a series of images I photographed of Podomyrma ants who had captured and were dismembering a Myrmecia worker, here. Nonetheless, they are a formidable adversary, so you can imagine my surprise when I happened across the scene below.

The culprit is a bark-dwelling thomisid in the genus Tharpyna. At one third the bullants size, it is a most impressive feat on the part of this spider. Click through to see the photo at full size and read more about what may have transpired.

Observational studies in ecology

Strictly speaking, sound ecological studies always involve some level of experimentation. However, in cases where no baseline data exists for the system in question, one has to resort to observational studies to determine all the factors involved. Conversely, one cannot depend on experimentation alone – you must understand the responses of your variables in the context of all possible factors. Controlled experiments, by their very nature, must exclude certain factors in favour of others.

The majority of my work done thus far has been observational and correlative, and although it has provided evidence of a number of pathways by which salinity can act to reduce riparian ecosystem function, further study is required to confirm these pathways and determine the exact causal mechanisms involved. This will require controlled experimental studies; the typical process by which causation is demonstrated, although even randomised experiments do not provide complete assurance of causal inference (Shipley 2000). This by no means dismisses the significance of field observational studies such as mine; observational and experimental studies in ecology should be complementary. Naturally assembled communities are determined by natural environmental variables and follow natural species assembly rules. Hence, they can differ from synthetic experiments in their response to changes in diversity as they take into account the inherent complexity found in natural systems (Diaz et al. 2003).

Observational studies provide a unique insight into the complexity of natural mechanisms and processes involved in determining how an ecosystem functions, and are necessary if one is to take a holistic approach in ecological work. Indeed, these are the very kinds of studies that have most commonly been employed in the past in spider ecology (see Bell 2005). However, it is important to note that one should not over overstate the results of such studies as they are not an explicit test of a hypothesis, but rather use them as the basis for additional experimental work.

After having collected much observational data, the next step is to follow it up with some good experimentatal manipulation to better ascertain the causal mechanisms at play. For me, this will most likely involve removing habitat diversity and vegetation structure in plots and looking at how different groups of spiders respond. They should, of course, respond according to the types of habitat they prefer – that is, loss of their preferred habitat should see a loss in the diversity and abundance of those spiders that utilise that specific habitat. These changes can then be related to the differences in vegetation, both within and between saline and non-saline sites, to give me a clearer indication of why I am seeing such marked changes to the spider community. Removal experiments are one possible way in which I can achieve this and gain a better insight into such disturbances as stream salinity and how they impact on terrestrial arthropod communities.

It’s in the way that she poses

When photographing ants, one of the things I hope for, besides the ant actually sitting still long enough for a shot, is that it will take up an interesting pose. To me, this makes for the best photos because it has a greater impact and presence than that of a regular photo. Of course, you can’t go past a photo with great technical details, but there is something special about a good pose that brings out the “character” of the subject – it may be in the way the ant holds its head, the arrangement of its limbs, or its position in relation to its surroundings.

Obviously you must take into account the composition as well: the depth of field, choice of magnification, focal point/plane, and the (presence/absence or type of) background are all important factors to consider. This of course requires some extra patience on the part of the photographer – it may take some time before the ant is in a favourable position – but it is definitely worth the trouble. I guess we are lucky in a sense, that ants are quite photogenic and are easily anthropomorphised, which makes them easier to relate to and enjoy photographs of.

Now, I am no master of composition by any means, but I like to think I have a few photos that stand out from the usual “snapshots” you can see in macrophotography. Below are some photos of ants I have taken that I am quite fond of (click through to see them at larger sizes).

Enjoy.

The project

Habitat destruction is a major contributor to global species loss. Often, the ecosystem in question and the fauna found within are poorly known, so that when such disturbances occur there is limited information available from which to draw on for successful conservation and rehabilitation programs.

Dryland salinity, as a result of large scale clearing for agriculture, is a significant anthropogenic disturbance in arid countries, especially Australia. Catchment areas are usually the first to be affected, however considerably little is known about the effects of stream salinisation on riparian terrestrial ecosystems. As part of my Honours project, I compared the diversity and abundance of the terrestrial arthropod fauna from both saline and non-saline sites of a stream that had its catchment area completely cleared, near Collie, Western Australia. Terrestrial arthropods play a critical role in the functioning of any ecosystem, so that any changes to them have the possibility to disrupt the numerous services they provide. My findings indicated a significant reduction in both the diversity and abundance of the terrestrial arthropod fauna. Looking at the results, it was apparent that this was primarily due to the predatory species, especially spiders. This is not surprising given that spiders are known to be dominant invertebrate predators, and that higher trophic levels are much more susceptible to change.

Previous work has also demonstrated changes to plant species diversity and composition at the same site. These correlations obviously posit a number of different hypotheses. Feel free to peruse my Honours thesis for further details and to get an idea of the other questions I am interested in.

One of the aims of my PhD project then, is to understand the (indirect) mechanisms by which salinity is acting to produce this change to the terrestrial arthropod community, especially the spider fauna. I am focusing on web-building and foliage-dwelling spiders so that I can ascertain the extent to which changes to their habitat (vegetation) impact upon the spider community. Do spiders require high plant species diversity per se, or is the reduction in number of species at higher salinities due to plant-mediated effects on their prey? Consequently, habitat diversity, vegetation structure and prey availability are of interest to me and these are the factors I will be concentrating on and manipulating in order to try and understand why I am seeing a change in the spider fauna at my study site.

As part of this project, I will hopefully become more familiar with the spider fauna of the southwest of Western Australia. This will mean more photos, be it via my camera or the microscope, hopefully culminating in a small field guide of my study area. I will probably also try and add a species list to this blog, eventually, with each taxon linking to a photo of it.

Stay tuned…