Friday, May 10, 2013

The effects of the butternut canker on the population of butternuts in North America

            For my ecology and management of invasive species class, we were required to give a presentation on an invasive species in North America.  For my presentation, I chose the butternut canker.  The canker, Ophiognomonia clavigigenti-juglandacearum, is actually a fungus that infects trees through any sort of scar or wound and quickly kills the branches it infects before eventually killing the tree.  The butternut canker is a prime example of just how devastating and unstoppable an invasive species can be if given the right environmental conditions. The fungus uses multiple vectors to travel from individual to individual; these vectors included rain and wind dispersal, insect dispersal, and seed dispersal.
            The butternut canker uses rain dispersal to move from their initial cankers on the lower branches of the crown to infect the stem of the tree; once an individual’s trunk has been infected, it usually dies within a matter of years.  Rain dispersal can also lead to infectection between trees when coupled with wind.  Butternut canker spores can be transmitted via aerosols, or tiny droplets of rain, which can travel up to 40 meters away from the tree.  Winds can also disperse spores a similar distance on their own.  What is truly terrifying is the fungus’s capability to disperse under prime conditions.  When temperatures are cool and there is a high relative humidity, spores have been found to travel over 100 meters away from the parent tree.
            Another common pathway that the canker uses to disperse its spores is via insects.  Beetle species such as the butternut circulio have bee found to carry as many as 8 million spores on one individual. In addition to this, the circulio creates both feeding and ovipositor wounds in butternut trees, providing the fungus with a direct route to infection of the host tree.
            The last method that the butternut canker uses for dispersal is through infected seeds.  The canker can survive in seeds at low temperatures for up to 18 months.  This is dangerous for 2 distinct reasons: first, it kills the young butternut while still a seedling and secondly, creates a new platform for the fungus to further transmit the disease. The fungus can live on dead trees for up to 20 months, meaning that it was plenty of time to disperse from a dead host tree to a new butternut nearby.
            Combating such invasive species is an incredibly difficult, uphill battle; no matter how much effort is put in to stop its spread, the fungus is already established in the United States and has been found across almost the entirety of the butternut’s range.  At this point, conservation of healthy butternuts is the only chance we have in preserving pure butternut trees in the wild; there have been hybrids of butternut and Japanese walnuts that are much more well adapted to resist the canker, but very few butternut trees have similar resistance.

Ecological Meltdown in Predator-Free Forest Fragmentations

             For my community ecology class, we read a paper regarding the ecological meltdown of multiple predator-free islands created via a hydroelectric plant in Venezuela. No top predators reside here, as the islands are separated from the rest of the tropical forest surrounding them.  This has left only predators of invertebrates, seed predators, and herbivores.  The effects have been extremely noticeable and have begun to create completely different communities from the ones found on mainland close by.
            The lack of vertebrate predators has caused for the density of herbivores to skyrocket to 10-100 times greater than can be found in the mainland forests.  Due to this high number, it is believed that top predators are key in limiting herbivore populations on the mainland.  These herbivores have done extensive damage to the local populations of seedlings and saplings from the canopy trees.
            While these species are usually maintained via top-down regulation, the lack of species above them on the food chain has enabled their populations to grow at exponential rates.  This will most likely occur until they become restricted again, this time via bottom-up regulation.  Eventually, the populations will be so large that the amount of vegetation currently on the island won’t be enough to maintain them.  Depending on how rapid this transition is, it is possible that some of these species will undergo the bottleneck effect.  This can be devastating to a species, as it is usually accompanied by a large loss of genetic diversity.
            These island communities are completely circumstantial and don’t provide much information in terms of successional processes in the tropical rainforest.  That being said, they do provide an extremely interesting look at how the removal of any given species can cause widespread changes to an ecosystem.  It will also be interesting to see how the transition into bottom-up regulation takes place and whether it is as drastic as it has the potential to be.


Spring Phenology

            We recently completed a lab in my forest ecology class about the timing of tree budburst in Jericho Research Forest.  The idea of the study was to look into how different trees respond to the onset of additional light in the spring.  When walking through the forest in early spring, it is very clear that different species are on their own schedules in terms of blooming; the first week we were out in the forest, approximately 75% of the trees showing signs of bud development were red maples.
            Such differences in tree phenology show how each species has a niche within the plant community.  Trees that bloom early in the season are able to absorb some extra light energy without the competition of the other canopy trees later in the season.  This is especially important for species that aren’t dominant trees in the overstory.  On the opposite end of the spectrum, there are also species that hang on to their leaves late into fall as to soak up the final rays of light before winter. Species such as American beech often won’t even release all of their leaves, and some stay on the bud for the duration of winter.
            We found higher amounts of saplings and seedlings budding than canopy trees.  While this is just speculation, I think that this could be related to the higher levels of light energy that they can receive earlier in the season, as the canopy trees aren’t shading them from the sun yet.  By budding early, they can take advantage of as much solar radiation as possible before they are stuck in the under the canopy once again.
            An interesting wrinkle to this experiment is the effect that climate change has already begun to have on spring phenology.  Studies of other New England forests over the course of 10+ years have shown that budburst is becoming slightly earlier every year.  With longer growing seasons, trees will be able to keep their leaves for a lengthier period of time.  This additional growing season will likely have an effect on the habitat range of different tree species.  

Invasional Meltdown on an Oceanic Island

             Invasive species can be one of the most disruptive disturbances possible for an ecosystem to encounter.  Once such a species has established itself within a community, the likelihood of effective management against it becomes minimal.  For my community ecology class, we were required to read a paper about the invasion of alien crazy ants (Anoplolepis gracilipes) on Christmas Island.  The ants have caused a catastrophic shift in the island’s ecosystem, and displaced the native keystone species.
            Before alien crazy ants invaded Christmas Island, the red land crab was a keystone species of sorts. It fed on the ground vegetation and seedlings in the understory of the local tropical rainforest, and did so extremely effectively.  This changed drastically with the introduction of the crazy ant.
            The crazy ant has been so impactful on the ecological community for many reasons. First, the ecosystem in place was a very simple one, making its susceptibility to potential invasions much higher and more devastating. This was compounded by the fact that the crazy ants routinely swarm and kill land crabs they come in contact with.  With the thinning of the crab population came the regrowth of the forest’s understory; species diversity has risen on Christmas Island since the introduction of the alien crazy ants.  Additionally, litter breakdown on the forest floor has decreased drastically.
            The crazy ants have also had an extremely negative impact on the canopy trees within the forest.  The introduction of crazy ants coincided with the introduction of a species that they have commonly had a mutualistic relationship with: the scale insect.  Scale insects congregate in canopy trees in high densities and generally lead to the introduction of sooty moulds. The mould leads to canopy dieback, and in some cases, the death of the tree itself.
            Since the introduction of the alien crazy ant on Christmas Island, the entire ecosystem that was in place has completely collapsed. The red land crabs that were once the keystone species keeping the forest floor clear of saplings are much less common than they were in the past, and the forest canopy that was once full has become fragmented due to the infestations of scale insects.  While it is extremely difficult to stop such invasions from happening, more effort needs to be placed into the development of effective management strategies for stopping the spread of invasive species.


The effects of nitrogen deposition on the carnivorous pitcher plant, Sarracenia purpurea

           I recently had a lecture on the effects of Nitrogen deposition on the northern pitcher plant, Sarracenia purpurea.  Through the burning of fossil fuels and the use of synthetic fertilizers, nitrogen oxides, nitrate and ammonium levels have risen over the past 100 years.  This has had an adverse effect on many different plant species, carnivorous species in particular.  Changing nitrogen deposition has led to changes in northern pitcher plants on both individual and population levels.
            Northern pitcher plants are perennials found in low-nitrogen peat bogs.  With a lifespan of 30-50 years, they live for an extremely long time in terms of most herbaceous plants.  Because of their low-nitrogen environment, pitcher plants rely on capturing arthropods in their water-filled pitchers as a source of nitrogen.  In fact, they aren’t the only species that rely on these arthropods; there is an entire community of insects and spiders that live inside of the pitcher plant’s pitcher. 
            To determine the effects that increased nitrogen levels had on the pitcher plant, my professor designed two separate experiments to compare the effects of anthropogenic nitrogen and nitrogen derived from prey species.  Through these experiments, he found that anthropogenic nitrogen led to changes in growth and morphology.
            The first experiment was centered on adding nitrogen and phosphorus to the plants anthropogenically.  It was found that instead of focusing energy on building their pitchers, pitcher plants exposed to larger amounts of nitrogen and phosphorus had larger phyllodia, which are their photosynthetically active leaves, and less shapely pitchers. The change in pitcher shape also led to lower levels of prey intake.  Additionally, they showed an increase in flowering probability.
            The second experiment that was executed was to test the effects of increasing nitrogen via prey intake. For this experiment, it was found that increasing nitrogen had no effects on the morphology of the pitcher plant.  These 2 experiments along with other studies have led people to believe that pitcher plants are now being limited nutritionally by phosphorus instead of nitrogen.
            The levels of nitrogen and phosphorus that pitcher plants are exposed to from a young age has also led to a decrease in juvenile survivorship, as well as lower population growth rates. This has made the population increasingly unstable; recent estimates have suggested that with not change to current nitrogen and phosphorus levels, the pitcher plant will likely be extinct within 650 years. If nitrogen levels continue to rise, that date could decrease to less than 100 years. 
            What must be considered is that pitcher plants aren’t the only plant species effected by rising nitrogen levels, and it is important that we realize the danger that many ecosystems as a whole face in the coming years.

lecture powerpoint:

Wind Power Proposal

There has been much debate recently regarding Vermont’s wind power suitability and the potential expansion of our wind power program.  Currently, there are 3 operating wind farms in the state with 3 more scheduled for future construction.  While public support is high for these projects, opposition groups have been very vocal against building any such turbines along Vermont ridgelines.  Even with such resistance to new wind power programs, Vermont’s overall interest in alternative energy sources is pushing this process forward, meaning that finding potential locations to place such turbines is imperative.
            The plan for creating a model for potential turbine sites is very similar to the locating a new town lesson found in the Dinamica instruction manual.  By narrowing possible sites via current land use cover, we can ensure that any locations won’t pose a direct threat to any important natural habitats. Additionally, sites will be restricted based on feasibility of construction, meaning that any areas that contain slopes too steep for truck access won’t be considered.  Lastly, wind power potential will be considered so that areas with high energy outputs will be preferential to those that would yield smaller figures.
            The functors that would be used to accomplish this map are a combination of Calculate Map and Calculate Categorical Map functors.  The calculate map functors will be used first to select data from the slope and wind energy maps and eventually to combine these inputs into a single map. The categorical map will be used to choose specific land use types that will be preferential to future wind power use.
            As society continues its search for viable energy alternatives to fossil fuels, renewable sources such as wind and solar power will continue to gain momentum due to their minimal toll on the environment.  This being said, one aspect that remains difficult to measure is the effect that any wind turbine would have on migrating bird populations that stop in Vermont on their paths north and south. Turbines have been documented as potential risks to local raptor populations, so it would have to be ensured that responsible planning occur to minimize any negative effects the turbines might cause.

Tuesday, March 19, 2013

The effects of changing polar climates on the world's ecosystems

            For the past 10-20 years, the shrinking of the polar ice caps has been an important ecological issue. These sheets of ice provide important services to many arctic and Antarctic animals.  The shrinking caps have endangered the livelihoods of many mammals such as polar bears, which rely on the ice sheets to be able to hunt in the Arctic Ocean.  New studies have estimated the total amount of ice that has been lost over the past 20 years.
            According to studies that have taken place from 1991 to present, both the Arctic and Greenland ice sheets have lost humungous amounts of ice.  To be exact, the Antarctic ice cap has lost 1,320 billion metric tons while the Greenland ice sheet has lost 2,940 billion metric tons.  This has caused the oceans to rise 11.1 millimeters, which constitutes 1/5th of the total sea level change over that time period. This doesn’t even factor in the losses taken on by ice sheets in Alaska, Canada, and Patagonia. In addition to the sheer amount of ice being lost, this shrinking process has accelerated to five times what it was in the 1990’s.  These changes made me think about the effects they might have on both arctic and aquatic ecosystems.
            The first effect that these changes will likely have is to decrease the temperatures of the oceans, albeit ever so slightly. The higher volume of water will heat at a slower rate than before. Additionally, there will be even less energy that makes it all the way to the benthic zones of the oceans, as the distances from ocean surface to bottom increases.  This eventual cooling of the oceans should have an impact on terrestrial climates as well; many climatic functions are affected by oceanic temperatures and cells that are created by air rising off of the ocean.  This decrease in temperature could potentially lead to colder temperatures at night in coastal regions, as well as cooler breezes during the day.
            While it is still too early to know the exact effects of the melting ice sheets at the poles, there is no doubt that there will be noticeable changes to numerous ecosystems across the globe. As these changes begin to take place, it will be extremely important both ecologically and economically to try and find solutions to any of the negative effects that these changes bring.