Cannibalism: Causes and Effects

Cannibalism: Causes and Effects CANNIBILISM IS RARE IN NATURAL SYSTEMS, IT IS GENERALLY NOT IMPORTANT FOR UNDERSTANDING POPULATION AND COMMUNITY DYNAMICS. DISCUSS. In ecology, cannibalism is defined as killing and consuming a conspecific individual. It can also be referred to as intraspecific predation. The key difference between cannibalism and other feeding acts such as necrophagy is that cannibalism relates only to conspecifics and includes the act of killing the prey or feeding on it whilst it is still alive. Cannibalism appears common in nature and has been recorded in over 1500 species. This essay will aim to highlight the fact that cannibalism is an important part of population and community dynamics in many natural systems. There are different types of cannibalistic behaviours that can occur. Size structured cannibalism is the consumption of a smaller or less advanced individual by a larger or more advanced individual. This is the most common type of intraspecific predation and takes place in a large variety of taxa including; 36 families of teleost fish (Smith and Reay 1991), crows (Yom-Tov), ground squirrels (Vestal 1991), dragonfly larva (Crowley et al 1987), isopods (Leonardsson 1991), reptiles (Keren-Rotem et al 2006) and salamanders (Rudolf 2006). Another form of size structured cannibalism is Infanticide cannibalism which is the consumption of the individuals own, or another conspecifics, offspring. Sexual cannibalism is when one member of a mating pair kills and eats the other member. This is restricted mainly to arthropods, insects and amphipods (Polis 1981). Cannibalism can even take place before birth as intrauterine cannibalism, where the largest embryos feed on smaller ones. It has been well studied in carnivorous sharks and teleost fish (Crespi and Semeniuk 2004). Sibling cannibalism can also occur amongst the newborns; this has been recorded in over 100 species (Polis 1981) and primarily occurs when the siblings differ in size or strength. Numerous studies have been carried out to discover if cannibalisms prevalence in nature relates to an important role in the dynamics of populations and communities. The majority of these studies have suggested that cannibalism may indeed have a large role in the regulation of many natural systems. When considering population dynamics, the components of the density dependent regulation of the population size is a major aspect. Cannibalism is of such importance in some species that it has been recorded as the main population regulating density dependent factor for them in their natural habitat. In young wolf spiders, this was tested using field and laboratory experiments (Wagner and Wise 1996). Field experiments showed that removing all natural enemies of the spiders did not reduce spider mortality as would have been expected if the population was regulated by predation. Also, increasing spiderling densities did not reduce the spiders prey density and only affected growth slightly, suggesting prey amount is not a key regulating factor. However, the effects of emigration could not be accounted for entirely which prompted more controlled experiments. These laboratory experiments showed that cannibalism and mortality rates amongst young spiders increased when prey availability decr eased, and higher densities exaggerated this effect (FIG 1.) Although this shows that cannibalism is sufficient to regulate the density of a population of wolf spiders, it does not confirm that in natural systems the enemies of wolf spiders are not the true cause of the mortality. It may only be when the natural enemies are removed that cannibalism takes over regulating the population density. In larval dragonflies it was shown that cannibalism was the main cause of mortality and that the amount of cannibalism was determined by density (Buskirk 1989). The mortality due to cannibalism was determined by comparing normal populations with populations that had their labial palps removed so they could not kill one another. It was found that non-cannibalism groups survived significantly better and this effect was greater at higher densities. The cannibalism groups showed reduced size distributions as only smaller instars were eaten. This meant that it was possible to fit the results to a predator prey model, that incorporated size structure, which indicated that cannibalism can affect size structure and result in a relatively lower number of young larvae. It is not uncommon for population structure to be affected by cannibalism; recruitment rate variations and biased age distributions have been accounted for by intraspecific predation in multiple species, such as teleost fish(Smith and Reay 1991), some polychaetes and molluscs(Polis 1981). Nevertheless, it has also being found that cannibalism can reduce fluctuations in recruitment rate by stabilizing population dynamics (Brownell 1985). Cannibalism in tribolium beetle populations was found to cause cycling in some life stages while stabilizing others (Benoit et al 1998). Separating the different stages of the lifecycle showed that the cycles in the larval and egg stages were due to larval cannibalism whilst cannibalism of eggs and pupa by adults stabilized the population structure and density. When adult cannibalism of pupa was stopped, the rate of population increase approached exponential. Although clearly an important factor in laboratory experiments, the effects of cannibalism in natural tribolium systems may be weakened due to many other factors influenced by density. Cannibalism can clearly have largely influential effects on the dynamics of individual populations, therefore any communities that these populations are involved in will also be affected. In IGP (Intraguild predation) systems, the predator, often omnivorous, and the prey share a common resource. Models not considering cannibalism designed to predict the structure of these food webs (Holt and Polis 1997) matched well with empiricial data found in studies with microbial systems (Morin 1999) but not others. The four main predictions of the non-cannibalism models were: For coexistence, prey must be more efficient at exploiting the common resource and predator must significantly gain from eating prey. The prey can survive at a lower amount of shared resource but in high enrichment conditions the predator will cause the extinction of the prey by apparent competition. A decrease in predator density will increase prey, therefore decreasing the resource. Only in a small area of the shared space is coexistence possible. However, the models which included cannibalism made predictions which differ from these but match better with empirical data and the observed fact that IGP systems are stable (Holyoak and Sachdev 1998) and widespread (Arim and Marquet 2004) in nature. These models, which considered cannibalism (Rudolf 2007), found that if the predator is cannibalistic it can exploit resources more effectively which may enable it to exist at lower shared resource levels. A change in the effect of enrichment will also occur so prey extinction does not happen at high resource densities. Furthermore, if the prey is cannibalistic, a decrease in predators will increase the shared resource density. This is due to less resource consumption by the predator stage and little or no change in resource consumption by the prey due to increased mortality and feeding from cannibalism from the lack of predators. This study showed that cannibalism was found to support the coexistence of the intraguild predator and prey. However, this only represents the findings of the predictions of a model which has not yet undergone a great deal of scrutiny. Nevertheless, it illustrates the necessity to account for cannibalism to enable accurate predictions of community dynamics as cannibalism effectively establishes an additional trophic level and population feedback loops. Consequently, it is incorrect for food web theory to view cannibalism merely as a contributor to density dependent mortality that has no effect on interacting species (Hart 2002). Incorporating interspecific and intraspecific interactions into food web theory which account for the size structure of the populations will undoubtedly improve understanding of community dynamics. Due to these inter-population feedback loops, nonlinear interactions within predator and prey systems can take place (Rudolf 2008). When the prey has cannibalistic individuals and the predator consumes these individuals, mortality in the prey due to cannibalism is reduced (FIG 2. A). This is a density mediated indirect interaction, just as if the predator consumed non-cannibalistic prey, increasing competition between the cannibals and the predators (FIG 2 B). Cannibalism can affect the behaviour of the smaller individuals of the population in multiple species (Crowley et al 1987, Persson and Eklov 1995, Keren-Rottem et al 2006, Leonardsson 1991) causing them to change their habitat or their activity. These general predation evading responses by the smaller individuals will reduce cannibalism and have a behaviour mediated indirect interaction by decreasing the interspecific predation rate (FIG 2. C). Higher interspecific predation rates causing a behaviour change, therefore reducing intraspecific predation(FIG 2 D) is also an behaviour mediated indirect interaction. These indirect interactions reduce the predators overall impact on the prey and can cause nonlinear relationships (Rudolf 2008). These nonlinear relationships have the potential to alter community dynamics significantly in predator prey systems with size structures. It is clear that to assert cannibalism as rare and unimportant in population and community dynamics is false. Cannibalisms regular occurrence in nature makes it undoubtedly a factor which must be considered as important. When cannibalism is considered within populations, both theories and empirical evidence have illustrated its varying impact on population dynamics. With this sort of influence at the population level, it seems surprising that an inclusion of cannibalism into general community dynamic theory is not common practice. Continued work by Volker Rudolf however, is showing cannibalisms role in predator prey interactions and trophic chains, yet empirical evidence of this is still lacking. Regrettably, until this has been collected, cannibalism may persist as possibly one of the most underappreciated factors that functions in community dynamics. The lack of studies investigating cannibalism in systems in which it appears scarce and unimportant is profound. Presumably, this is because it may seem meaningless to carry out or publish a study which proves cannibalism as non-existent or unimportant in a system that it was already previously assumed to be unaffected by it. For this reason, it is important to be vigilant when estimating the importance of cannibalism on a whole in understanding population and community dynamics. Nevertheless, to allow theories concerning population demography, predator prey interactions, trophic chains and other interactions to be implemented into natural systems, it would certainly be beneficial to consider cannibalisms role.

All Day Kindergarten Essay

After critically analyzing the current kindergarten scheduling trends, there is a shift in many schools from half-day kindergarten programs towards full day kindergarten programs. A full day kindergarten or all day kindergarten program is a program in which pupils attend school each weekday for approximately six hours. The growing number of all day kindergarten programs can be attributed to a change in the American society and education in general. To be specific the growing number can be attributed to the increase in single parents and dual employment households and finally a general belief that all day programs better prepare children for school. There has been a looming legislation, which is going to give powers to the local, state and federal governments to control standards of education. Kindergarten education is targeted by this piece of legislation because it promotes all day kindergarten programs at the expense of half-day programs. I fully support this piece of legislation that promotes all day kindergarten programs because of the benefits that are inherent with the program. It’s my prayers that the legislation is approved so that our schools can start churning out very competitive graduates. I believe all day kindergarten programs are the best because of the following: †¢ A research conducted in 1990s reported a consistent positive academic outcome for all children enrolled in all day kindergarten programs. A subsequent research also showed that children who attended all day kindergarten programs scored higher points on standardized tests than their half day counter parts. Hough and Bryde found out that there is more individualized instruction in all day programs when compared to half-day programs. Individualized training makes it possible for the teacher to understand each and every need of the pupil and therefore attend to them accordingly. A research carried out by Cryan and his friends found out that there was a positive relationship between participation in full day kindergarten program and later academic success. After comparing similar half day and full day programs in a nationwide study, Cryan found out that full day kindergarteners exhibited more independent learning, classroom involvement, and productivity in work with peers and reflectivity than half-day kindergarteners. †¢ Other researches pointed out that there is a clear relationship between the kind of kindergarten program and the children’s behavior. Teachers rated children in all day kindergarten higher. (Cryan et al, 1992). Other researchers who have studied social and behavioral outcomes found out those children in all day kindergarten programs were engaged in child-to-child interactions and this had a positive effect in building their learning, communication and social skills. (Elicker & Mathur, 1997). The full day kindergarteners were more likely to approach the teacher; they expressed less anger, shyness, withdrawal and blaming behavior than half-day kindergarteners. †¢ Both teachers and parents whose children were enrolled in all day kindergarten proved that all day programs better prepared children for their first grade. They also indicated preference for all day kindergarten because of the more relaxed atmosphere, more time for creative activities and more opportunity for students to develop their own interests. The teachers also concluded they had more time to know the children and their families thus enabling them to better meet the children’s specific needs. (Elicker & Mathur, 1997) It’s definite that there are more positives in all day kindergarten programs but it’s important to remember that what the children are doing during the day is more important than the length of the day. Experts are warning administrators and parents against full day kindergarten programs that are academically rather than intellectually engaging in tone. Some of the intellectually engaging activities that should be incorporated in all day kindergarten programs include the following: 1. Programs that emphasize language development. 2. Programs that offer balance of small group, big group and individual activities. 3. Programs that asses pupils’ progress through close teacher observation and examination of pupils’ work. 4. Programs that develop children’s social and interpersonal skills including conflict resolution strategies. 5. Programs that involve children in first hand experience and informal interaction with objects, other children and adults. (Rothenberg, 1995) To successfully implement this project, the government should commence creating space and teacher capacity. It should also set aside enough funds to make sure the schools can afford equipment necessary for all day kindergarten programs. References Cryan, J. R. , Sheehan, R. , Wiechel, J. , & Bandy-Hedden, I. G. (1992). Success outcomes of full-day kindergarten: More positive behavior and increased achievement in the years after. Early childhood research quarterly, 7(2), 187-203. EJ 450 525 Elicker, J. , & Mathur, S. (1997). What do they do all day? Comprehensive evaluation of a full-day kindergarten. Early childhood research quarterly, 12(4), 459-480. EJ 563 073. Hough, D. , & Bryde, S. (1996, April). THE EFFECTS OF FULL-DAY KINDERGARTEN ON STUDENT ACHIEVEMENT AND AFFECT. Paper presented at the annual conference of the American Educational Research Association, New York: ED 395 691.

Sat Essay Samples 6 - an in Depth Anaylsis on What Works and What Doesnt

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Supply Chain Management within the Healthcare Sector

Supply chain management With the aging of the population and the increasing developments of technology, healthcare facilities are more and more pressured to provide high quality medical services. This increasing stress associated with the changing needs of the population forces the healthcare providers to also develop and to adjust their operations. Specifically, they are informally required to place an increased emphasis on the administrative and business side of their operations. In this specific order of ideas, the role of supply chain management increases (Uzsoy, 2005). In a traditional setting, supply chain management would integrate the totality of operations and processes which ensure that the product is created and delivered to the end consumer (Handfield, 2011). Within the setting of healthcare provision, the supply chain management would refer to the totality of the operations which ensure that the medical act is created and delivered to the patient; this medical act includes both the services of the medical teams, as well as the medical products required, such as medical equipments, beds, MRI machines, or medicines. At a primary level, the supply chain would be formed from the primary manufacturers, followed by the secondary manufacturers, the distribution centers and the wholesalers. From the wholesalers, the medical equipments and pharmaceuticals would be transmitted to hospitals and clinics. 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