Lessons from the Lion

            In the epilogue of Where the Wild Things Were, Stolzenburg proposes the question..."Are humans now functionally equivalent to large mammalian carnivores?" I would answer him yes, and that unfortunately we do not manage populations in the same beneficial ways as a natural predator (there are exceptions to this).  We are too efficient predators. If a hunter wants to remove entire populations in a short period of time, he/she has to technology to easily do so. Humans have the power to negatively impact populations by complete removal, where as natural predators are healthy and essential regulators of populations.

            Think about comparing the human predator to a lion. The priorities and hunting modes of each predator are both different and similar. In some cases, both the human and lion could be considered sit and wait predators. Imagine lions laying low in the grass and hunters posted in tree stands. However, hunting priorities of the human and the lion are very different in that the lion's contribution is sustainable. The lion goes for young, old, or weaker individuals, where as the human goes for the individual with genetic perfection. Thus, the human removes individuals that need to pass on their genes to keep the population fit and adaptable.  

            Since we did eradicate natural top predators from certain ecosystems, maybe it is now our duty to take the place of the top predators. I was recently watching an episode of Wild Ohio that was describing drastic declines in native wild flower populations due to over grazing by deer. Many parks in Ohio since the 90s decided to implement public hunting to facilitate declines in deer populations. The park ranger hosting this episode ended his segment with this statement..." It is much easier to find "volunteers" to hunt and manage deer than to participate in invasive plant removals". This ending statement is disheartening and implies that the hunters are concerned only about the benefits of hunting, for whatever reasons (food, profit, the "thrill"), and that conservation of the ecosystem is an after thought. Of course, this is not to be said about ALL hunters and there must be some hunters that consider themselves conservationists. 

Top down versus bottom up

Where the Wild Things Were discusses examples of ecosystems from the point of view of trophic cascades. Since this topic is new to me, I decided to dedicate this blog to a short review about top down versus bottom up forces. Bottom up is where primary producers and nutrients dictate community structure and diversity. It seems that ecologists predominantly think that consumers (ex. top predators) impact producers (ex. plants) but are not the key components driving productivity in ecosystems. Thus, most ecologists appear to prefer bottom-up control of species productivity and biodiversity. However, this topic is highly

debated and recent papers show that top predators can alter entire systems and convert habitats ( ex. overgrazing by herbivores due to lack of predators converting savannas to deserts). In these instances, studies show that top predators can benefit plants by controlling densities of herbivores. Most likely different ecosystems respond differently to both top down and bottom up presurres. These papers give several interesting examples that highlight the importance of top predators in ecosystem diversity. One study looks at "islands" in the Venezuelan rainforest with and without top predators (see Figure 4). This study shows that top down control highly effects community diversity. Islands without predators showed high densities of herbivores and seed predators resulting in a decreased number of seed recruitment and saplings. Another example can be seen in Western Atlantic salt marshes (see Figure 5). This study shows that marshes can be over run in the absense of the top predator the blue crab.  In this case, the prey of the blue crab is a snail who lives on fungus growing on plant tissue. Large numbers of this snail have been shown to deplete marsh vegetation and expose mudflat patches in the absence of the blue crab. Based on these papers, it seems like there is a combination of both top down and bottom up pressures in ecosystems. In some ecosystems, it seems that humans play a huge role in altering trophic levels by removing predators or top down forces resulting in loss of diversity and habitat integrity. 

Silliman, B. R. & Angelini, C. (2012) Trophic Cascades Across Diverse Plant Ecosystems. Nature Education Knowledge 3(10):44

Top predators: Active vs. sit and wait ambush

           Stolzenburg discusses extensively the detrimental effects of the removal of wolves from Yellowstone National Park. Tree saplings such as Aspen and Cottonwood were being consumed at a fatal rate by the over abundance of Elk. Once all wolves were removed from the park in the 1920s, Elk became more and more abundant on a steady diet of tree saplings. It was at this time that populations of these trees species were threatened to the point that they may not recover, all because the top predator (the wolf) was removed.

            The removal of wolves from Yellowstone shows the important role that top predators have on different ecosystem processes. I wanted to find other examples of the roles of top predators in ecosystems and came across a paper by Schmitz (2008) entitled, "Effects of Predator Hunting Mode on Grassland Ecosystem Function". This paper addresses the idea that top predators are essential to ecosystems while also introducing another interesting concept. Schmitz postulates that different modes of hunting of top predators can have differential cascading effects on ecosystem processes.

From Schmitz (2008)

            Schmitz distinguishes two separate modes of hunting; there are active hunters that have wide ranges and there are predators that "sit and wait" and ambush their prey. Active hunters may alter species densities by capturing and consuming, but may not cause chronic behavioral changes in prey. Alternatively, sit and wait predators can cause behavioral responses, or shifts in foraging, in prey because they must continually respond to ambush from predators in a set location. Schmitz hypothesizes that these two distinct predator modes will alter ecosystems in different ways.

            To test his hypothesis Schmitz used grassland ecosystems containing Solidago rugosa , a dominant competitive plant species, along with other herbaceous species (preferred by grasshoppers). Grasshopper species graze upon these plants species while being predated upon by two different predatory spiders; one that actively hunts, and one that sits and waits. Schmitz observed varying ecosystem responses when each type of spider was removed from his treatments.

            Schmitz's findings suggest that the actively hunting spider reduces the numbers of grasshoppers, thus having a positive effect on grasses and S. rugosa. Alternatively, the sit and wait predator may cause a foraging shift in grasshoppers from the preferred nutritious grasses, to the more common S. rugosa which could be considered the "safer" plant to forage. Ultimately, grasshoppers must choose between feeding on preferred grasses and quickly taking refuge from predators, or feeding on S. rugosa (the dominant plant). Overall, this paper introduces an additional variable (different hunting modes) that should be considered when analyzing the role of top predators play in ecosystems. 

The first bite: The beginnings of predator-prey interactions on our planet

            In Where the Wild Things Were, Stolzenburg discusses the very first predator, which was most likely part of the “primordial soup” that generated multicellular organisms. I imagine during this time there were intense and viscous predator-prey interactions. Cells were being engulfed entirely (eating your neighbor whole!) or sucked up by some sort of apparatus or appendage. See this quote from Stolzenburg...

            “It was a natural step or two beyond that for predator and prey to add  spermlike tails and fluttering cilia of rudimentary self- propulsion, the first glimpses of the chase.”

One of the best (in my opinion) endosymbiotic diagrams 
from Keeling (2010) The endosymbiotic origin, diversification and fate of plastids 

            Scientists have discovered evidence of this predation.  Plastids contain relict prey membranes, still present and observed in most all plastid-bearing organisms. For example, early glaucophytes (a small group of algae) retain an extra membrane containing peptidoglycan (only found in the cell walls of bacteria). This wall is likely a remnant of the cyanobacteria that was preyed upon by early glaucophytes. It is fascinating that we are able to trace this sort of ancient predator-prey interaction.

           

            It is interesting to think about what sort of environmental pressures led to the first predation of one single celled organism upon another. Even further, what steps led to the permanent integration of this prey cell? What sorts of genes were transferred and how many millions of years did it take? Was the beginning of multicellularity ultimately driven by predator- prey interactions? I believe that scientists are just beginning to answer these questions with the amazing advances in genomics.

Didinium preying upon Paramecium (sciencephoto.com)

            Can you imagine what the first endosymbiotic event looked like? Are there any examples of predation that we can compare it to today? I imagine it looked something like one of the experiments that Stolzenburg describes with Didinium preying upon Paramecium. Gause, a microbiologist from the 30s, added Didinium to colonies of Paramecium and watched as the Didinium devoured every last Paramecium. He then added sediment to the bottom of the jar. Didinium again consumed most Paramecium, however a few were able to take refuge in the sediment. This simple experiment is interesting from a predator-prey perspective for several reasons. It shows how environment also plays a role in these interactions. Also, how predators drive niche specialization by causing prey to take refuge in different environments.

WATCH Didinium hunt and eat Paramecium.....

http://www.youtube.com/watch?v=HlHihxqqXOE

or...

http://www.youtube.com/watch?v=rZ7wv2LhynM

            

Ancient shipwrecks

 Weisman illustrates the counter attack of nature if humans where to disappear. He also describes areas of the planet where humans once existed, but nature prevailed, as if we really did disappear. Shipwrecks can be eerie, remind us of the power of nature, and also gives us a glimpse in the past.

One of the most rare shipwrecks ever discovered is the Kyrenia Ship, an ancient Greek ship that was discovered off the coast of Northern Cyrpus. Wiesman describes the watery scene in detail. It is amazing what can be preserved in the absence of oxygen; the Kyrenia ship is the only example of a perfectly in tact merchant ship.

The ship’s hull was discovered by Andreas Cariolou perfectly intact, although the wood needed to be injected with polymers or else it would disintegrate when exposed to air. The hull was constructed of the Aleppo pine, a pine that is native to the Mediterranean and held together by copper nails, resistant to rust. 

The Kyrenia ship was known to carry wine, olives, and almonds. Interestingly, scientists were able to carbon date the almond seeds and date the ship to over 2,300 years old. I wonder if there will ever be a time in the future when someone will carbon date the seeds agriculturalists use today.  Will future humans even need seeds? It is interesting to imagine current humans as an ancient population and what future generations would think of us.

How did this ship go down you might wonder? It is difficult to determine the fate of this ship because it was found underwater in pristine condition. There were no signs of battle wounds. Scientists speculate that piracy or simply old age might have contributed to the sinking of this fascinating ship. The Kyrenia ship is considered an archeological treasure, still giving us much information about the past. To learn more about this ship check out the BBC documentary.