Social ‘Meltdown’ in the Demise of an Island Endemic: Allee Effects and the Vancouver Island Marmot

The Allee effect is a biological phenomenon originally proposed by Warder Clyde Allee. This phenomenon is characterized by a sharper decline in an already diminishing population once it is reduced past a certain threshold. The effect is driven by a shift to an inverse density-dependant relationship; the population becomes so small that, rather than increasing, it shrinks as population density decreases. Although the Allee effect has been observed in some controlled experiments, it is rarely documented in nature and attempts to stimulate it outside of a highly controlled environment are often impractical and unsuccessful. Despite this, Brashares et al. (2010) have conducted a study in which they not only observe the Allee effect take place naturally in the population of the Vancouver Island marmot, but also document the causes which induce it. This makes theirs one of few papers to present empirical evidence of the mechanisms of the Allee effect in a wild population. Their results indicate that some of the actual causes of population decline as density decreases are: larger home ranges and increased difficulty in finding mates, diminished ability to detect and evade predators, and a decrease in foraging, either to make more time for vigilance or because a more bountiful environment was compromised for a safer one. Further knowledge of the mechanisms of the Allee effect, and the thresholds at which populations reach it, may be very important for population forecasts and conservation in the face of oncoming climate change. —Emily Cole
Brashares, J., Werner, J. R., Sinclair, A. R. E., 2010. Social ‘meltdown’ in the demise of an island endemic<!–[if supportFields]> XE “endemic” <![endif]–><!–[if supportFields]><![endif]–>: Allee effects and the Vancouver Island marmot. Journal of Animal Ecology 79, 965973.

Brashares and his colleagues conducted their study, in part, through the use of the behavioral observations of the Vancouver Island marmot (VIM) gathered by D. C. Heard in 1973, 1974, and 1975. At that time the population of the VIM was stable at about 350 individuals. Using these observations, and a contemporary set that the researchers collected themselves, Brashares et al. were able to make a comparison between the behaviors of the VIM of a stable population, and those of an inverse density-dependant population. They also drew from observations of contemporary congeners of the VIM at stable populations. In order to reduce bias and error, the researchers used the same methods as Heard when collecting and analyzing data whenever possible. Heard collected his samples in the Nanaimo Lakes area of Vancouver Island. Brashares and his fellow researchers also made observations at the Nanimo Lakes area, as well as an additional site, Mt Washington, from 2002 to 2005. Over this period they observed a total of 38 individuals, which at that time comprised 70% of the population. The researchers made their observations by means of binoculars and spotting scopes, and were always 40300 m away from the animals. They also gathered data from radio transmitters implanted into the marmot’s ears, which allowed for effective tracking. A. A. Bryant describes the implantation of these transmitters in his 1999 report, Metapopulation ecology of Vancouver Island marmots. Many of the marmots were already embedded with the transmitters, however the researchers did implant a small number each year to compensate for deaths. 
The researchers found drastic differences in the behaviors of the populations of the 1970s and the 2000s. The contemporary marmots exhibited much larger home ranges, those of males up to 45 times larger and females 30 times larger than those of the past. Social behavior was widely varied as well, with the marmots of the 2000s interacting with each other at less than one twentieth the rate of their ancestors.  In addition, when they did interact, they demonstrated significantly fewer greetings, and significantly more aggressive behaviors such as fighting and chasing. Finally, modern marmots were far more active during midday than historic, and far less active during morning and evening. They devoted more time to belowground activities and when aboveground, more time to vigilance. In total, modern marmots spent less than 15% of the time foraging that their 1970s counterparts did.
The researchers believe that these behavioral changes are, for the most part, related to the modern decrease in population and population density of the VIM. They argue that the increased home ranges are a result of the increased distance between colonies, which forces the marmots to travel farther in search of both mates and safety. In addition, their social behaviors are perceived as a possible result of natural selection for personality types more fitted to a less populated environment. Finally, the marmot’s shift in time management is also viewed as a development of their more unaccompanied lifestyle. A separate historic study, Schwartz and Armitage (1997), demonstrated that solitary marmots spent up to twice the time on vigilance that their more social counterparts did.
While it is rare to see the Allee effect manifest in a wild population, the Vancouver Island marmots appear to be a clear case. In addition their behaviors suggest the mechanisms by which low population density depletes small populations. As the Allee effect represents a sharp positive feedback cycle, it is easy to see how more research on its mechanisms and the population thresholds at which they come into effect could benefit species conservation. Especially in the anticipated environmental changes ahead.  

When Climate Change Affects Where Birds Sing

While the effect of climate change on animal behavior is a known and visited topic, rarely do researchers delve into the effects of climate change on sub-categories of animal behavior, such as communication. In this experiment Møller (2010) studied the effects of climate change on sound through documenting changes in the height of song posts selected by songbirds. This was the first experiment to study the effects of climate change on vocalizations. Møller hypothesized that an increase in air temperature could alter sound absorption and through this, affect birdcalls. He also predicted that vocal communication could be affected by a change in plant phenology<!–[if supportFields]>XE “phenology” <![endif]–><!–[if supportFields]><![endif]–> brought on by temperature change and an increase in rainfall. Møller believed that these effects would manifest themselves in an overall change in song post height. He also believed, however, that these changes would be complicated by several variables, namely, sexual competition, susceptibility to predation, height of surrounding vegetation<!–[if supportFields]> XE “vegetation” <![endif]–><!–[if supportFields]><![endif]–>, and migration. To test these hypotheses Møller collected two sets of data on songbird post height, 20 years apart. —Emily Cole
Møller, A. P., 2010. When climate change affects where birds sing. Behavioral Ecology (Advance Access Publication).

Møller chose the village of Kraghede, Denmark to serve as the study sight. He collected data during the months of April, May, June, and July from 1986–1989 and then again in 2010. The area was 25km2 and consisted of farms, houses, open fields, hedgerows, woodlots, shrubs, and trees. The exact same area was studied during both periods of the experiment. To gather data Møller walked through the area recording no more than a single individual at each site. This was to avoid recording one bird as two. Birds don’t travel much during their breeding season so this was most likely an effective method. Møller recorded both the position of the bird on the vegetation<!–[if supportFields]> XE “vegetation” <![endif]–><!–[if supportFields]><![endif]–> and the maximum height of the vegetation using his own height as a comparison. He recorded all height values in multiples of his own height. In order to verify this method he used a hypsometer, an instrument that measures height, in addition to his visual judgment for 300 observations. The results of the two separate methods were extremely close. Møller collected mean temperature and rainfall data from April through August 1971–2010 for his study from the Danish Meterological Institute.
          Møller expected that song post height would depend on many variables, the first of which being song post habitat. He felt that species living in habitats with higher vegetation<!–[if supportFields]> XE “vegetation” <![endif]–><!–[if supportFields]><![endif]–> would necessitate higher song posts. To compensate for this he rated habitats on a three-point scale using 0 to represent grassland<!–[if supportFields]>XE “grassland” <![endif]–><!–[if supportFields]><![endif]–>, 1 to represent brush and scrub, and 2 to represent forested areas. If a species fell into both categories he assigned it the higher number.
In addition Møller predicted that the results would be affected by sparrowhawk predation, with more susceptible species showing lower song post heights. Thus he employed another numerical scale where 0 implied a species of bird was consumed as much as would be expected from it’s abundance, +1 implied that it was being consumed 10 times more frequently than would be expected from it’s abundance, and -1 implied that it was being consumed 10 times less frequently than would be expected. A higher number implied that a species was more susceptible to predation and would most likely have a lower song post height.  
Møller also hypothesized that song post height would be influenced by sexual competition within a species. He thought that species with higher levels of sexual competition would exhibit higher song post heights. He anticipated two situations in which a species would experience higher levels of sexual competition: species with growing population trends, and species in which the male and female were different colors.
Finally Møller anticipated that the results would be influenced by whether a species of birds migrated or not. He believed that migrating species were less likely to quickly adapt their phenology<!–[if supportFields]> XE “phenology” <![endif]–><!–[if supportFields]><![endif]–> to a changing environment than their residential counter-parts, and thus more likely to experience impaired environmental conditions. To account for this he recorded an estimate of each species migratory distance by averaging the northern most and southern most latitude for both the breeding and wintering locations and then subtracting the wintering mean from the breeding one.    
Møller found that many climatic aspects for April–August did indeed shift from 1971–2009. The mean temperature increased by 2 °C or almost 20% and annual precipitation increased from about 250mm to about 300mm or by about 30%. Møller concluded that such a change in temperature and rainfall would only produce negligible changes in sound absorption, if any, and thus discarded his hypothesis that this would affect song post height. However, song post height did increase on average 1.2 m, with species deemed more susceptible to sparrowhawk predation showing a smaller increase than those less preyed upon. While Møller did not find any significant changes in relation to migration, species anticipated to have higher levels of sexual competition showed a larger increase than others, as did those singing in higher vegetation<!–[if supportFields]>XE “vegetation”<![endif]–><!–[if supportFields]><![endif]–>. Møller stressed that this was not simply a case of birds singing in higher vegetation having higher options for song posts than those in lower areas, such as grassland<!–[if supportFields]> XE “grassland” <![endif]–><!–[if supportFields]><![endif]–>, because such areas often contained barns and other high posts. He found his results to be consistent with the idea that changes in plant phenology<!–[if supportFields]> XE “phenology” <![endif]–><!–[if supportFields]><![endif]–> led to this increase in height. This article is an excellent example of the broadness of variables that need to be examined when anticipating the effects of climate change. 

Predicting the Effect of Climate Change on Aggregation Behaviour in Four Species of Terrestrial Iso-pods

On the subject of biological organisms and climate change some topics are studied more than others. Changes in territory, migration, morphology, and breeding patterns are all frequently examined, however less often studied are animal behaviors that attempt to cope with extreme climate through modifying it. Hassall et al. (2010) performed one such study in which they investigated the ability of woodlice to alter their microclimate by aggregating, or gathering together in tight groups. This behavior allows the woodlice to reduce their individual water-loss, both by decreasing the area of their bodies exposed to the air, as well as by creating a moister microclimate around the group. The researchers studied the tendency of the lice to aggregate in environments of altered temperature, humidity, and vapor pressure deficit (VPD), the difference between the current level of moisture in the air and the amount it holds at saturation. The scientists found that those species of woodlice more physically disposed toward water loss gathered together more frequently at higher temperatures and lower humidities, indicating an ability to adapt to climate change, through the technique of altering microclimate. —Emily Cole
Hassall, M., Edwards, D. P., Carmenta, R., Derhé, M. A., Moss, A., 2010. Predicting the effect of climate change on aggregation behaviour in four species of terrestrial isopods. Behaviour 147, 151164.

Hassall et al. studied four different species of woodlice: Armadillidium vulgare<!–[if supportFields]> XE “Armadillidium vulgare” <![endif]–><!–[if supportFields]><![endif]–>, Philoscia muscorum<!–[if supportFields]> XE “Philoscia muscorum” <![endif]–><!–[if supportFields]><![endif]–>, Oniscus asellus<!–[if supportFields]> XE “Oniscus asellus” <![endif]–><!–[if supportFields]><![endif]–>, and Porcellio scaber<!–[if supportFields]> XE “Porcellio scaber” <![endif]–><!–[if supportFields]><![endif]–>. A. vulgare, which is native to drier habitats than the other species, was the best equipped for preventing water-loss. O. asellus and P. muscorum were the least protected and P. scaber possessed an intermediate level of fitness. The woodlice were collected from two different areas. O. asellus was collected from Norwich, UK in January of 2006 while the remaining species were collected from Corsham, Wiltshire, UK in August of 2006. Throughout collection the woodlice were kept at a constant temperature of 17 °C.
In order to test the tendency of the woodlice toward aggregation, the researchers placed ten individuals into a petri dish which was divided into eight equal segments with a marker. The largest and smallest 5% of the population were not used, and age and gender were allowed to fluctuate randomly. The lid of the petri dish had a hole cut into the top, which allowed air to circulate, and the dishes were placed into an environmental chamber, highly controlled for humidity and temperature, for 20 minutes. At the end of the experiment the dishes were carefully removed and the number of woodlice in each segment was counted. In the event that a woodlouse lay in two segments, it was counted as being in the one that over half its body was in. If the louse was exactly between segments it was counted as being in the segment in which it’s head lay. When woodlice were found sharing a segment it was interpreted as aggregation. The researchers performed two different sets of tests, testing P. scaber with O. asellus as well as with P. muscorum and A. vulgare. The two separate groups were tested at different temperatures and humidities.
Hassall et al. hypothesized that aggregation would increase with decreasing humidity and also with increasing temperature, even at a constant VPD. They also predicted that the species which possessed more physical adaptations to prevent water-loss would aggregate less frequently. Their findings were supportive of their hypotheses. They found that, with the exception of the woodlouse most adept at water conservation, A. vulgare, all of the species aggregated significantly more at lower humidity and at higher temperatures. P. scaber, the species, which after A. vulgarewas most water-loss resistant, aggregated less frequently than O. asellus and P. muscorum. The researchers saw no significant difference in aggregation resulting from fluctuating VPD, which suggests that the behavior is closely related to temperature. This in turn indicates that woodlice will respond to climate change by aggregating more frequently. As different species aggregated more frequently than others, these responses will most likely be species specific. The extra time spent aggregating may come at a cost to foraging or reproduction, and the fact that this behavior necessitates several individuals to be viable, could spark an Allee effect, should the population slip beneath a certain density. Further study is needed to better predict the effects increased aggregation would have on the terrestrial isopod population.

Climate Change-Induced Hybridization in Flying Squirrels

While there are many studies examining the effects of human activity on biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>, fewer examine the anthropogenic effects on the evolutionary mechanisms that govern biodiversity. This study, conducted by the research team Garroway et al. (2010) takes a closer look at one such mechanism: hybridization. For this experiment, the researchers examined the DNA of two separate species of flying squirrel, Glaucomys volans<!–[if supportFields]> XE “Glaucomys volans” <![endif]–><!–[if supportFields]><![endif]–> and Glaucomys sabrinus<!–[if supportFields]> XE “Glaucomys sabrinus” <![endif]–><!–[if supportFields]><![endif]–>. Though the two species classically reside in habitats that are close but not overlapping, a recent series of warm winters, brought on by global climate change, led G. volans to expand it’s territory 200 km north, and into that of G. sabrinus.The researchers hypothesized that this would create instances of hybridization between the two species. They found that not only were there examples of genetic hybrids between the two species but that there was also evidence of backcrossing without extensive introgression, implying that the hybridization was recent and therefore an indirect result of the recent climate change. This is likely the first report of contemporary climate change acting as a catalyst in the creation of new hybrid<!–[if supportFields]> XE “hybrid” <![endif]–><!–[if supportFields]><![endif]–> zones. —Emily Cole
Garroway, C. J., Bowman, J., Cascaden, T. J., Holloways, G. L., Mahan, C. G., Malcolm, J. R., Steele, M. A., Turner, G., Wilson, P. J., 2010. Climate change induced hybridization in flying squirrels. Global Change Biology 16, 113–121.

The researchers collected specimens through live trapping in two separate locations. The first was Ontario, Canada<!–[if supportFields]> XE “Canada” <![endif]–><!–[if supportFields]><![endif]–> where they designated 26 different sites ranging from the north shore of Lake Erie to the southern edge of the boreal<!–[if supportFields]> XE “boreal” <![endif]–><!–[if supportFields]><![endif]–> forest<!–[if supportFields]> XE “boreal forest” <![endif]–><!–[if supportFields]><![endif]–>, which encompassed the original upper bound of G. volans’s habitat prior to its 200 km northward expansion.  They collected specimens here from 2002–2004. They also conducted live trapping at 19 sites in Pennsylvania<!–[if supportFields]> XE “Pennsylvania” <![endif]–><!–[if supportFields]><![endif]–>, USA . The results from this study site showed that all remaining G. sabrinus populations in the state were coexisting with G. volans, indicating a widespread shift in habitat.
Once the squirrels were trapped, the researchers obtained their DNA through removing 20–30 hairs and suspending them in a solution at 37 °C for 12 hours. After processing the DNA the squirrel’s genotypes were analyzed and scored. Each animal was assigned a Q value, which represented the amount of that individuals genome devoted to a certain species. An individual was defined as highly assigned to a species if it’s Q value was greater than 0.95 for that species. Hybrids were defined as individuals with Q values greater than 0.20 but less than 0.80.

Using these criteria, the researchers discovered a total of 11 hybrid<!–[if supportFields]> XE “hybrid” <![endif]–><!–[if supportFields]><![endif]–> squirrels, which constituted 4% of the population sampled. They also found squirrels with Q values high enough to be assigned to one species but which also contained genetic markers for the other species. These were assumed to be the offspring of hybrids who had crossed back again with the parental species, or possibly, but less likely, with another hybrid. They were taken as evidence of hybrid fertility. As there were instances of extensive introgression the researchers concluded that the hybridization was recent and most likely an effect of the new habitat boundaries. While the researchers conceded that hybridization can be a positive result if it aids in adaptation, they also stated that it is generally considered a negative process as it results in a net loss of biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>. This article exemplifies some of the effects that can be expected when a species copes with climate change through migration rather than adaptation. 

Resting Time as an Ecological Constraint on Primate Biogeography

The act of resting is not often treated as an aspect of animal behavior that directly impacts survival, and is more frequently perceived as time that could be used for other activities. While this is true of some resting time, animals do need a certain amount, known as enforced resting time, to perform necessary biological processes such as regulating body temperature (thermoregulation) and digesting food. In turn, the amount of resting time an animal requires can affect where it is able to live. In order to demonstrate this, Korstjens et al. (2010) performed an analysis of climate and common animal behavioral data. The team of scientists chose to focus on primates for this analysis because they are frequently studied, and have a wide range of dietary specializations and geographic distributions. The scientists compared observation data on primate resting times with dietary needs as well as social groupings and climate data. They found that while the percent of the day a primate spent resting was significantly affected by social group size, annual temperature variation, and the percentage of leaves in the primates diet, only temperature variation and percentage of leaves significantly affected enforced resting time. In addition, the researchers found that the minimum amount of enforced resting time a primate required affected it’s geographical location. These discoveries bring new insight to

models that predict how a species will fair with the oncoming climate change.—Emily Cole

Korstjens and her partners chose data sets for this analysis based on several parameters. The data had to include observations on resting time, diet, and group size, and had to have been carried out over 8 months or for multiple seasons. If a data set failed to meet these requirements it was not used. The scientists then compared these data to several climatic variables, including average annual rainfall, average annual temperature, variation from month to month of rainfall, and monthly variation of temperature. These data were either gathered by the same scientist who made the primate observations, a colleague or, in the absence of these, through the Willmott and Matsuuras climate model<!–[if supportFields]> XE “climate model” <![endif]–><!–[if supportFields]><![endif]–>.
The scientists found three parameters that significantly affected resting time. Dietary needs, specifically the amount of leaves consumed, were one. Primates who’s diet was made up of more than 33% leaves (folivores) needed far more resting time than those who consumed fewer leaves, presumably to aid in digestion. The monthly variation of temperature was also found to have a significant effect, especially on folivores, with higher variation leading toward more resting time probably because more thermoregulation was required. It was also hypothesized that temperature could affect the quality of the foliage consumed by the primates, thus heightening it’s impact. The size of the social group the primates participated in also significantly affected resting time, however the researchers argued on theoretical grounds that this only affected uncommitted resting time and not the enforced resting time of interest.
From the data, the researchers were able to extrapolate an equation that predicted the minimum amount of enforced resting time a generic primate would require based on monthly temperature variation, the constraints placed on this by mean annual temperature, and the amount of leaves in the primates diet. Using their equation, the researchers found that the predicted resting time was significantly higher for areas in which primates were absent, than for areas in which they were present. This implies that resting time does influence geographic distribution. This is most likely because places that require too much enforced resting time draw time away from other vital activities, such as foraging. The researchers found that almost any area that required more than 33% of the day for rest was uninhabited and inferred this to represent the maximum enforced resting time, above which it would difficult for a species to sustain itself.
Using their new-found equation, the researchers went on to predict the enforced resting times for primates that would be needed in scenarios of climate change where the mean temperature would rise by 2 °C or 4 °C. They found that nonfolivore distributions would remain relatively unaffected in the 2 °C scenario, while African folivore distributions would be largely affected in either case. South American folivore distributions, however, would remain largely unaffected in the 2 °C scenario as well. The scientists hypothesized that this was due to the fact that South American primates are largely arboreal, while their African counter-parts are often at least semi-terrestrial.
The findings imply that enforced resting time plays a key component in both the survival and distribution of a species. As such, this paper presents yet more important aspects to consider when predicting the effect climate change will have on animal behavior and, ultimately, biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>.

Colobus Monkey Parasite Infections in Wet and Dry Habitats: Implications for Climate Change

The effect of climate change on animal behavior is an often-studied phenomenon, however the effect of climate change on animal relationships is a less frequently examined sub-topic. In this experiment, Chapman et al. (2010) studied the host parasite relationship and the likely changes it will encounter, should climate change grow more severe. Using the colobus monkeys of Kibale National Park in Uganda as a model, the researchers created a comparison between the monkeys frequenting wet habitats, and those that preferred drier ones. The researchers took fecal samples from the monkeys and analyzed them for gastrointestinal parasites. Two forest sites were chosen for this experiment, Kanyawara and Mainaro. The monkeys were studied in three groups, those who frequented the wet lowlands and dry highlands of Kanyawara, and those who frequented the highlands of Mainaro only. The researchers found that in all cases, the moneys in the wetter areas did show increased instance of intestinal parasites. The effects of parasites such as these on the colobus population have yet to be determined, however some theories suggest that they could be extreme. As climate change is expected to make some drier areas wetter, these findings have implications for the future of colobus monkeys and many other animal populations as well.¾Emily Grace Cole
Chapman, C., Speirs, M., Hodder, S., Rothman, J., 2010. Colobus parasite infections in wet and dry habitats: Implications for climate change.  African Journal of Ecology (In Press).

The researchers chose two study sites for their difference in rainfall per year, but also for their similarities in forestation. While Kanyawara is 30 km north of Mainaro and receives 361 more mm of rain, both sites have comparable biodiversity of the tree community with similarly sized trees, although the species content of the two forests does differ. Primate densities at each site were generally alike, with the exception that Cercopithicus mitis was not present in Mainaro.
Fecal samples were collected from groups of moneys that frequented the highlands and the lowlands of Kanyawara, and also those who frequented the highlands of Mainaro. As colobus monkeys have a small home range, it is unlikely that one group visited both areas. Samples were only collected in May and June of 2005 and 2006 to avoid a seasonal skew of the results. Prior to processing, the samples were stored in a solution of 10% formalin. They were then processed using sodium nitrate and evaluated visually for intestinal parasites.
          The researchers found that the monkeys living in wetter areas showed higher amounts of gastrointestinal parasites. The prevalence of specific parasitic species such as Trichuris sp. was found to be higher, the wetter the area. In addition, the species richness of the parasite community was found to be higher in the lowlands of Kanyawara than in the drier highlands, while both of these areas exhibited higher species richness than the drier Mainaro site.
          While it is not proven that gastrointestinal parasites have severe effects on the populations of their hosts, some studies have suggested they do, especially when their hosts are pressed for food. Chapman et al. also offer up the postulate that since climate change has been shown to alter growth patterns in plants, sometimes inducing food scarcity, it could exacerbate parasitic effects. In any case, the effects of climate change on the host parasite relationship is certainly relevant to the future of many animal populations.

Squeezed at the Top: Interspecific Aggression May Constrain Elevational Ranges in Tropical Birds

The effect that climate change will have on many endangered species is currently a hot topic in the field of environmental analysis. While many sophisticated predictions are being made in terms of the abiotic impact climate change will have, rarely do researchers take biotic effects into account.  Jankowski et al. (2010) performed an experiment that explored one possible biotic aspect that will influence species survival in the event of a temperature change, namely, niche habitats and the species interactions that maintain them. The researches studied tropical birds in the Cloud Forests of Costa Rica, who are known for their strict elevational distribution. By playing pre-recorded bird songs to target birds, the researchers tested the hypothesis that the birds use interspecific competitive interactions to enforce their spatial boundaries. The results the researchers obtained indicated that the bird’s ranges were enforced as a result of interspecies competition, and that when combined with the effects of climate change, this dynamic could lead some species to extinction far sooner than anticipated through abiotic considerations alone.¾Emily Grace Cole

Jankowski, J., Robinson, S., Levey, D., 2010. Squeezed at the top: interspecific aggression may constrain elevational ranges in tropical birds. Ecology 91(7), 1877-1884.

  While the mechanism the birds use to maintain their range is still in debate, this is the first study to provide experimental evidence supporting the theory that the birds use interspecific competition to maintain their elevational boundaries rather than phenotypic specialization or some other attribute. Jankowski et al. experimented with five species of bird, two of which were known to inhabit lower forest elevations: the White-breasted Wood-Wren and the Orange-billed Nightingale-Thrush, two of which inhabited higher forest elevations: the Gray-breasted Wood-Wren and the Slaty-backed Nightingale-Thrush, and one, the Black-headed Nightingale-Thrush, which inhabited a narrow strip between the other two Thrushes. Each of these birds has been known to maintain strict elevational boundaries and is highly subject to species replacement.
In order to discern whether these birds were maintaining their elevational distribution through species interactions, the researchers played pre-recorded birdcalls, both from birds of the same species and from birds of a different species but the same genus, to the target birds. The target bird’s behavior was observed and recorded before the recordings, after the first recording, and after the second recording. The researchers established the extent of each species’ territory by listening to birdsong and watching individual birds’ movements. They played the recordings to birds at varying distances from the edge of their territory, to see if they exhibited a distance-based change in behavior. A recording of either the Golden-crowned Warbler or the Lesser Greenlet, which are both known to cohabitate at many elevations, was also used as a control. No differences were found between the target bird’s behavior before this recording and after it however, so these behavioral observations were added to the general pool of uninfluenced target bird behavior.
          The researchers found that the birds of each genus responded aggressively to the songs of birds from the other genus, indicating that there was interspecies competition. In addition, in almost all the species, aggressive reactions grew stronger closer to the edge of the territory where the chances of meeting an outside bird increased, indicating that the aggressive behavior was learned, and therefore flexible, allowing for responses to change based on population density, etc. Finally, it was detected that certain species showed more aggression in their reactions toward the birdsong of other species than vice versa. This demonstrates a certain interspecific dominance, which could have large repercussions should the climate change. If, for example, the higher elevation species was subordinate and warming were to allow lower dominant species to expand into higher elevations, the subordinate upper elevation species would then be forced into an even smaller amount of land, possibly too small to sustain it’s population. In an alternate scenario a dominant upper elevation species could prevent the expansion of a lower elevation subordinate species, squeezing it between the dominant species’ territory and the increasing temperature. In this case at least, biotic factors play a key role in anticipating the effects of global warming on endangered species.    

Study and Design of a Hybrid-Diesel-Compressed Air Energy Storage System for Remote Areas

In Canada it is estimated that throughout the country, over 200,000 people live off of the grid, and require electricity from other sources. Most of this electricity is supplied through small, localized power plants containing diesel generators. This situation is not ideal for several reasons. Primarily, diesel itself is not the most efficient or inexpensive way of generating energy. However local power plants in Canada suffer other economic stressors too; it is far more expensive to run a small power plant than it is to run a large one, and the costs and risks associated with the transport of the diesel to the plant add further financial burdens. Some locations are more remote than others, and this is reflected in the cost of fuel transport, however as Canada has a uniform price for energy, some plants lose much more money than others. For all of these reasons these small power plants expend more money than they receive, and need to be subsidized by the Canadian government. On an additional note, diesel also releases a high amount of greenhouse gas. Diesel electricity production emits 1.2 million tons of greenhouse gas per year in Canada alone. Ibrahim et al. (2009) conducted a study in which they attempted to mitigate many of these issues through hybridizing the current diesel generators with a combination of wind turbines and a compressed air storage system.  While it was already known that the addition of wind turbines to these generators could cut fuel consumption modestly, the authors found that with the added addition of a well-designed supercharger fueled by the compressed air storage unit, they could reduce fuel consumption at a much higher rate.¾Emily Grace Cole

Ibrahim, H., Younés, R., Ilinca, A., Dimitrova, M., Perron, J., 2010. Study and design of a hybrid-diesel-compressed air energy storage system for remote areas. Applied Energy 87, 17491762.

 While wind-turbine, diesel-hybrid generators did exist before Ibrahim and his colleagues conducted their study, they have many known disadvantages. Low penetration systems, in which the overall energy derived from wind is no more than 1015% are viable, however a larger amount of wind energy usage would lead to even more reduction in fuel consumption. The issue lies in the unpredictability of wind energy. In higher penetration systems, where the overall percentage of wind energy contribution is higher, the generator must often be left on so that in the event of a loss of wind it can respond quickly and deliver energy. This is a major fuel drain, as the generator can remain on for long periods of time, serving no actual purpose. Energy storage is a solution to this, as it allows the wind turbines to harvest and store excess energy when they are producing more than their load demands. In this scenario, the generator can then be powered down, and energy reserves can be drawn on from storage in the event of fluctuation. However the current storage systems have their flaws as well. Some systems use hot water to store energy quickly but hot water is difficult to convert back to electricity, and the reserves must be quickly accessible. Batteries are used as well, but they are expensive, need to be maintained, and are difficult to dispose of. Fuel cells are a possibility too, but they are not commonly used, as they are expensive and technically challenging. Compressed air does not have these disadvantages. It is clean and it converts back to electricity efficiently and quickly.
The addition of compressed air storage to wind-diesel-hybrid systems alone would increase wind penetration and therefore cut down on fuel use, however compressed air has another advantage in that it lends itself to supercharging. Supercharging is a process which facilitates the injection of air into the combustion chamber of the diesel generator, giving it greater power for the amount of fuel it uses, leading to an overall decrease in the amount of fuel it needs. Ibrahim and his colleagues designed several possible models for implementation of the supercharger into the existing Canadian diesel generators. The models varied in their use and placement of the compressed air, as well as their number of turbines. They were all thought to bring different advantages and disadvantages. In order to select which model to proceed with in the study, the researchers came up with a weighted rating system based on the following criterion, in order of descending importance: efficiency, simplicity, adaptability with the diesel engine, cost, control system, and reliability, system 1, which relied upon one turbine directly connected to the supercharger shaft, was judged to have the highest score.
When Ibrahim and colleagues experimented System 1 in practice, they found that it led to a significant fuel saving, as the generator could be made to work at 25-30% of it’s original fuel consumption.