April 20, 2012
A comparison between Catalina and Santa Cruz Islands
One characteristic shared by the two islands is how susceptible their ecosystems are to disturbance, as exhibited by the crashes of their island fox population. Although different in cause, each demonstrated that a small island ecosystem, evolving under sheltered protection from mainland disturbances can create unique and fragile ecosystems that do not handle major disturbances well. This is largely due to their relatively small gene pool of the population and small geographic range.
Island Fox
In other more traditional geographic regions, a disturbance in an ecosystem that leads to a population crash can often be followed by an easier recovery. Either there is a large enough, well-adapted surviving population that can repopulate, or organisms from another region can gradually be reintroduced into the area. However on an island, often neither is possible. If the species experiencing the crash is endemic, then it is possible that the crash will result in the species extinction as no other existing members of the species exist in the world. Even if some individuals survive the initial disturbance, with the population, small to begin with, may leave so few survivors that the gene pool does not carry enough diversity for a proper recovery and the species may die out. As such, a disturbance in an island ecosystem is much more likely to lead to species extinction.
On Catalina Island, the collapse of the fox population was primarily due to the introduction of the canine distemper virus. In 1999 an outbreak occurred causing the population to drop from 1300 to only 100 animals. The outbreak swept across the west side of the island but fortunately did not reach the eastern island, which was separated by a narrow isthmus. In 2000 the Catalina Island Conservancy and the Institute for Wildlife Studies instituted the Catalina Island Fox Recovery Plan, which consisted of monitoring, captive breeding, vaccination, and relocation of the foxes. The program was a success and by 2004, the population had climbed up to 300. Although it is not entirely known how the virus was introduced into the population, one theory is that it was brought to the island by an infected domesticated dog or a stow-away raccoon.
Feral Pig
On Santa Cruz Island, a collapse also occurred, but for different reasons. Over-predation by the golden eagle, an exotic species, was discovered to be the primary cause. However indirect blame could be placed on the human introduction of pigs to the island. A study by Roemer et. al. indicated that the colonization of Golden Eagles onto the island could only be sustained by the existence of a feral pig population. However, even though the foxes alone could not sustain the eagle population, they were much more affected by eagle predation than the pigs. The foxes were ill adapted to evade eagle predation and as such faced possible extinction.
Golden Eagle
Like the island fox’s unfortunate fate at the hands or claws of introduced species and viruses, many native and endemic plant species on both Catalina and Santa Cruz islands have suffered from human introduced grazers. While both islands have gone under some form of plant restoration from the damages done by past-introduced grazers, Catalina currently still has resident populations of non-native grazers while Santa Cruz Island does not. This provides an interesting contrast between the islands because there are many similar native plant species that exists on both islands but in different quantities and manifestations. Through this comparison one can clearly see the tremendous impact that grazers have on the plant communities of the Channel Islands.
Catalina Island Bison
Catalina currently has a small population of 150-200 bison that roam the island. The bison population is controlled both by a birth control that limits the number of calves a female bison can have a year and by shipping the bison back to the mainland to supplement mainland herds on tribal lands. The birth control method was introduced in 2009 and was greeted by animal rights activists who opposed the Catalina Conservancy’s earlier eradiation of feral goats and pigs with high power rifles from helicopters. The Los Angeles Times reported that the birth control option for controlling the bison herds was suggested by an animal activist Avalon shop owner named, Debbie Avellana. Other non-native grazers that continue to roam the island are mule deer that are kept under control by recreational hunting as well as the Conservancy, and a very small population of black buck antelope. Historically Catalina was used for grazing goats, pigs, sheep and cattle but have since been irradiated.
Catalina’s current native plant population has suffered as a result of the current non-native grazers on the island. The effect of the grazers can be seen all too clearly in the example of the native Giant Coreopsis (Coreopsis gigantea). On Catalina this “Dr Seuss plant” is only found with in the confines of the Ackerman Nursery where grazers are kept out. There are also reports of some wild species on the sea bluffs or steep gullies of the island where grazers can’t get to them. On a whole plants on Catalina tend to be bush-like where they otherwise would be more like trees. The only “trees” you will find on Catalina are either non-native or are the native toyon, lemonade berry, sugar bush or Catalina Cherry trees because they are so resilient. Some native plants have changed their pollination season to try and outcompete not only the grazers but also invasive plants.
Restoration on Catalina is difficult because there is a permanent human population there and the island attracts around a million tourists a year. This constant stream of visitors means the potential for foreign species introduction is more likely. Fennel is still a problem on the island being an aggressive invasive species, but a management strategy including weeding around campsites and populated areas outward seems to be working in its early stages. Another invasive species is the eucalyptus, which was brought to the island on purpose to beautify areas like Avalon and was a favorite of the Wrigleys. Santa Cruz Island also struggles with both eucalyptus and fennel.
Tourists in Avalon
Santa Cruz Island does not have any non-native grazers currently living on the island. Historically Santa Cruz Island was a ranch raising some of the most well known beef and sheep products on the west coast. Since then it has been brought under the control of National Park Services and the Nature Conservancy. The only human presence is that of campers and eco-tourists, and researchers. There are a few people that live there to maintain the research and historic ranch facilities. These conditions have allowed a recovery of many native plants and allows for these plants to grow large and where on Catalina you may have a sparse bush, on Santa Cruz Island you will have a large bush as tall as a man. On Santa Cruz Island, Giant Coreopsis and Bedstraw are significantly more common than on Catalina as are buckwheats (including one species of buckwheat that is endemic to Santa Cruz Island), Manzanita (also including a endemic species), and Sunflower bush. Santa Cruz Island has around 600 native plant species.
Santa Cruz Island Landscape
These cases, exhibit how island ecosystems are incredibly susceptible to disturbances, which can often be brought upon by the interference of humans. In the case of Catalina Island Fox, the introduction of a virus, possibly by a colonizer’s pet dog, is to blame for the collapse of a species. Santa Cruz’s population collapse was brought upon by the human introduction of pigs to the island, which facilitated the entry of yet another harmful invasive species. It is believed that in both instances, had humans not brought in these disturbances that such a collapse would not have occurred. Just as these collapses wouldn’t have occurred without human interference one can use Santa Cruz Island to “see” how different a landscape Catalina would have if it didn’t have the human introduced grazers still shaping plant communities on the island. As such these cases serve as a reminder that humans should exercise extreme caution when interacting with such isolated ecosystems, as they can be as fragile as they are unique and beautiful.
This post was written by Mariah Gill ’12 and Jefferey Nakashioya ’12 both seniors in Environmental Studies.
References:
http://www.catalinaconservancy.org
http://iws.org/species_islandfox_SCat.html” http://iws.org/species_islandfox_SCat.html
http://articles.latimes.com/2009/nov/20/local/la-me-catalina-bison20-2009nov20″ http://articles.latimes.com/2009/nov/20/local/la-me-catalina-bison20-2009nov20
Carlos de la Rosa, Personal Communication/ Lecture
I also thought it was interesting to note how skunk populations were affected by the hyper-predation of the foxes by the golden eagles. Prior to the introduction of eagles of Santa Cruz, the foxes outcompeted the skunks on almost all fronts. The eagles, as they colonized the islands relied heavily on pigs to sustain their diet because pigs offer enough substance to feed such large birds of prey. However, in 1994 when the gold eagles were arriving at the island they noticed much easier to catch abundant indigenous prey, the island foxes. Since the island fox was much more abundant than the island skunks, to reasonable prey species for the eagle, and since the island fox is much more active during the day than the nocturnal island skunk, the eagles tended to hyperpredate the foxes, causing the largest proportion of their diet to be composed of the island fox by the time of their removal. This led to the skunk population increasing in size dirastically since they did not have to compete with as many foxes. This goes to show how ecosystem dynamics are so fragile and how great of an effect small changes, introducing eagles and pigs, can have on an entire ecosystem.
The presence of tourists on Catalina Island is an interesting factor affecting the presence of native wildlife species and their potential endangerment. Not only can tourists transport new species via boat travel, but they can also have a huge effect on the conservation efforts taken against an invasive species, or to preserve a native one. It was clear after hearing from people that live/work on the island how loud the voice of one noisy island resident can be if given the right situation. For example, attempts to deal with the feral cat population was confounded by locals protesting without the adequate ecological knowledge of the problem. I feel a similar situation could arise if efforts were taken to eradicate an invasive plant species that was somehow attractive to a layperson who did not know of the species potential ecosystem effects.
In the cases of the invasive plant species, they surely would not get such a strong hold if it wasn’t for the humans who clear the land and create the disturbance in the first place. If you think about the places on Santa Cruz where we saw the most invasive plants, they were all around the human dominated places-on cleared lands that used to be the ranch and all along the roads. It definitely makes us feel better about restoring the land, but in some cases, restoration is impossible. To eradicate native grasses, filaree and scarlet pimpernel would not only be time intensive, but would take more money than anyone is willing to invest. Soon enough these ecosystems will evolve with these non-native species in place. We can help foxes restore their populations, but it makes me wonder about how hard it would be to not only eliminate non-native and invasive species of plants, but then assure that their regeneration efforts will be successful. There is a limit to the actions that we can undo, and, was said in the post, we must be very cautious and consider all possible outcomes of even small development projects we think will be harmless.
In addition to Mariah’s mention of anthropogenic impact differences on Catalina and Santa Cruz Island, It is important to note that it doesn’t a stop at the terrestrial and ocean boundary. As mentioned above, Catalina Island is subjected to much more human impact than Santa Cruz Island is. In fact, Avalon beach is the most populated area of all the Channel Islands, and because of this the National Resource Defense Council has called out the beaches of Avalon of being one of the dirtiest in the nation- failing beach water quality tests 73% of the time on a consistent basis. This is primarily caused by the out-dated and corroded sewage system that the city has still yet to update because of the surmounting economic toll it would have on tourism and the city. The system is flushed with corrosive sea-water to the point where untreated human sewage is seeping into the beach water and more importantly the groundwater that is relied on for drinking. As can be judged from common sense, the pollution that enters the beach does not just sit there. It greatly affects the surrounding marine protected areas that surround the perimeter of the island and could be detrimental to some of the endangered marine species that live in this unique ecosystem, including the kelp beds they count on to survive.
If Avalon wants to keep making its hundreds of millions of dollars in tourism revenue, it should start thinking about improving its infrastructure first.
Source: http://articles.latimes.com/2011/jul/10/local/la-me-avalon-water-20110710
http://www.catalinachamber.com/
Another factor about the differences between the two fox population declines that I find very interesting is the role of natural selection in the extinction process.
As mentioned in the blog post, the Catalina fox population decline was due to the introduction of canine distemper virus. Lucky, the presence of the isthmus and the human population of Two Harbors served as a natural shield from letting the virus spread to the other half of the island – the foxes carrying the disease did not cross the isthmus because the human population makes a barrier in the area.
The fox population on Santa Cruz Island on the other hand was in danger because of hyperpredation, involving the feral pig and the golden eagle.
Comparing these two situations from a natural selection point of view is interesting. If a Catalina fox contracts canine distemper virus, it basically has no other fate but to die. However, on Santa Cruz Island, natural selection plays a larger role. The foxes can outsmart the hyperpredation by changing their lifestyle – for instance if they were to become more nocturnal like the skunks, they could avoid getting hunted. As a direct example of natural selection, the faster and smarter foxes are the ones that would be able to survive in relation to the slower foxes. The faster and smarter foxes would live on to pass on their genes and the next generation has the potential to exhibit those genes as well.
In conclusion, I still believe that the hyperpredation was an awful occurrence for the Santa Cruz Island Fox population, but I also think it would be interesting to do research on the foxes that were left at the end in comparison to the regular population to see if this situation exhibits natural selection in any way.
Another interesting comparison that can be made is the differences between the number and types or Marine Protected Areas on both Catalina and Santa Cruz islands. Overall, among the Northern Channel Islands, there is a higher number of State Marine Reserves (the highest order of protection): 10 out of 14 protected areas; whereas only 3 out of the 11 protected areas of the Southern Channel Islands exist as State Marine reserves. What is more interesting however, is that Santa Cruz only has 3 protected area, 2 of which are SMRs. Catalina on the other hand, has 9 protected areas – 6 State Marine Conservation Areas (with limited catch), 2 no-take SMCAs, and only 1 SMR. I found this interesting considering how ideally, MPAs are best placed in the healthiest of current marine ecosystems. With such protection of the terrestrial land on Santa Cruz and so many anthropogenic pressures negatively affecting the land and adjacent waters of Catalina, one might expect to find a greater number of SMRs and SMCAs around Santa Cruz. With no permanent settlements on Santa Cruz, the marine environments are not subject to the associated pollutants, which is important to note, especially in light of what Sherwood mentioned about the corroded sewage system in Avalon that’s seeping into the ocean. This could have potentially harmful effects on the SCMA, “Casino Point,” along the northern shoreline adjacent to Avalon Bay, which a popular recreational diving area for tourists. I can’t imagine that the waters around Catalina are more suitable for establishing MPAs than the more pristine marine environments around Santa Cruz. As far as I’m concerned, increased efforts should be made to establish more SRMs around Santa Cruz Island.