Evolution, Ecology, and Genetics
Evolution, Ecology, and Genetics BIOCORE 301
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This 6 page Class Notes was uploaded by Miss Camden Hauck on Thursday September 17, 2015. The Class Notes belongs to BIOCORE 301 at University of Wisconsin - Madison taught by Staff in Fall. Since its upload, it has received 45 views. For similar materials see /class/205305/biocore-301-university-of-wisconsin-madison in Biology at University of Wisconsin - Madison.
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Date Created: 09/17/15
Response and recovery pattern similarities between mangrove forests and Caribbean coral reefs after hurricane activity When the destructive power of a natural disaster is revealed to the general public damage is conveyed in human terms in the losses felt by the civilized world following each catastrophe While cameras capture the obvious damage often characterized by leveled neighborhoods submerged cars and boardedup shop windows the injury to biological systems underlying modern society is usually ignored When recent hurricanes ravaged the southern Gulf States they not only sent entire cities packing but also toppled the delicate balance organisms maintain with their environment Reefs and mangrove forests two of the region s major coastal habitats are like rainforests of the sea representing a huge amount of diversity When these communities are disrupted by outside forces more is harmed than their external structures The repercussions of a disturbance as large as a hurricane may still be observed years after the most dramatic and immediate changes are noted Longitudinal studies of tropical storm damage in a variety of habitats have revealed how the complex yet interconnected nature of individual environments contribute to their recovery Despite the obvious physical attributes that separate aquatic and terrestrial biomes a strong connection can be made between the two concerning their response to a devastating storm Recovery and regeneration of the biomass studied in these two spatially disconnected ecosystems Caribbean coral reefs and coastal mangrove swamps in the continental US follow a strikingly similar path that is not yet fully understood Despite the mystery surrounding the complex nature of survival and competition in this unique situation research teams have begun working towards characterizing the long and shortterm response to substantial damage of these rich habitats TERRESTRIAL IMPACT AND RESPONSE Mangrove forests are typical around the mouths of large rivers where sediment levels in the water are high Their unique roots trap debris and organic material which over time help to gradually slow the river s ow and protect the coastline from erosion Groves where sediment buildup has been relatively undisturbed may actually facilitate the extension of coastal terrain Mangrove root systems are also specially adapted to the brackish conditions in which they are usually found deep saltfiltering tap roots preserve a stable cycling of usable water while aerial roots rise above water levels providing lateral stability and oxygen transport In addition the tree s seeds have adapted to this unique landsea environment by developing a tough outer layer that ensures buoyancy creating the opportunity for germination either on the parent tree between limbs for example or wherever tidal waters carry them Due to this unique opportunity for dispersal a mangrove forest may have substantial species diversity Tan 2001 Each type of tree depending upon its age height or species may respond differently to hurricanes Entire forests made up of this mosaic of traits employ very dynamic mechanisms to deal with the life and death of their components The initial and most apparent change that occurs in a mangrove forest after a storm is the large decrease in biomass due to wind and wave action Sherman et al 2001 Even in cases where the hurricane passes by at a considerable distance removal of the forest canopy can be devastating In the Dominican Republic Hurricane Georges traveled fifty kilometers south of a grove of mangroves killing 42 of the basal area a measure of regional occupation by a particular species defined as the sum of all trunk crosssectional areas Sherman et al 2001 Trees that did survive suffered considerable damage the consequences of which were not fully apparent until later a mortality rate of 9 by density was observed between seven and eighteen months after the hurricane an increase of 7 over the typical prehurricane amount Differences in mortality can depend on site factors such as tree age rooting methods soil conditions and general forest structure as well as specific adaptations that species have developed over time to reduce their susceptibility to damaging winds Sherman et al 2001 One of the primary trends noted in large expanses of mangrove forest is that unevenaged stands with canopies of varying heights are more prone to injury due to increased wind turbulence caused by a rougher canopy surface As a result of heterogeneous defoliation and a general decrease in biomass understory light levels increase dramatically Sherman et al 2001 A typical mangrove swamp will have minimal shrub and small tree growth but in the months following a hurricane light penetration is no longer hindered The exposure of the understory can facilitate regeneration of trees as saplings no longer have to compete with established mangroves for crucial resources like light However the opportunity also arises for other plant species to begin ourishing in the newly created gaps The mangrove fern is a common example of a destructive competitor during reforestation densities as high as 3000 plants per hectare 1 plant every 3 m2 after hurricane activity have been recorded At such a substantial concentration ferns may reduce light levels enough to inhibit mangrove sapling growth and hinder future steps in the recovery process Sherman et al 2001 Successful regeneration of mangrove forests is often due to speciesspecific adaptations in foliage morphology Researchers have offered the theory that a tree s ability to go through rapid defoliation followed later by equally fast refoliation may actually be a helpful adaptation reducing wind resistance on the entire organism and therefore decreasing the possibility for further stem and trunk damage Sherman et al 2001 While researchers continue to develop hypotheses surrounding the mystery of forest recovery it is important to note that nature is not a static system favoring tranquility Repeated major storm systems and other disturbances may in fact be an important factor in the maintenance of the distinctive structure of mangrove forests and their continuing evolution as keepers of the landsea frontier AQUATIC IMPACT AND RESPONSE With a level of nutrient richness similar to that found in mangrove forests the Caribbean coral reef system serves as habitat for a multitude of other life forms and depends signi cantly on dramatic change and often damage to preserve its diversity Hurricanes in combination with other stressors may either establish mortality as a routine and beneficial event in the reef environment or promote the total degradation of the region depending upon intensity and timing of these external events Bythell et al 2000 In a 2000 study ofa US Virgin Islands reef site the effects of two weeks of intense hurricane activity following several decades of mass epidemics in primary reefbuilding coral species were observed Mortality was significant following the storms as is common across the Caribbean where coral cover is typically reduced by N 17 in the year after a hurricane impact Gardner et al 2005 Despite the sheer destruction that powerful waves caused below the water s surface the region eventually saw sustained increases in overall coral cover and species richness Interestingly the areas of the reef most severely damaged exhibited the most dramatic improvement in community structure and diversity Successful recruitment of coral heads was dominated by species new to the area and appeared to be related to the elimination or reduction of some competitor or predator that previously limited such growth Bythell et al 2000 In the absence of competition just as in stands of damaged mangrove trees the establishment of new colonies becomes less of a struggle Broken fragments of neighboring colonies have a greater chance of successfully attaching to the skeleton of the damaged reef and creating a new community Due to this new mosaic of surviving species the reef studied in the Virgin Islands actually demonstrated relative stability with respect to community composition Although individual sections of the reef may experience very different effects due to hurricane forces and other stressors such as disease the overall dynamic remains essentially unchanged Further evidence of the importance of hurricane activity in coral reef evolution involves the observation that in sites unaffected by storms in the previous decade coral loss was more than three times higher than in recently impacted sites Gardner et al 2005 Hurricanes therefore prompt a form of rapid natural selection reducing the amount of susceptible corals present in the reef and leaving space for survivors to proliferate In future disturbances storms will have less opportunity to damage the reef if only the strongest have continued to succeed in the environment While recovery in most cases promotes optimism in casual observers it should be noted that prestorm levels of almost every aspect of reef health may not be reached even eight to ten years after impact Gardner et al 2005 The highly variable nature of an organism s response to storms diseases human pressures and overall climate shifts of different intensities and frequencies forces researchers to note that not one single factor is central to a reef s diversity Bythell et al 2000 While clearly in uential in the life of a coral reef hurricane impacts remain a relatively mysterious intermediate in the ever evolving struggle between maintaining species diversity and avoiding extinction of reef inhabitants In their attempts to define the complex relationships and mechanisms present in nature that determine if a species will fail or not researchers have identified common elements present in the recovery processes of different coastal landscapes In both mangrove forests and coral reefs individual species appear to have developed certain adaptations to either avoid reestablishment in the same environment buoyant seeds for example or minimize damage during future storms It has also become obvious that while the destruction brought on by a hurricane may be extensive the absence of a dense and established population of organisms may actually promote the introduction and success of new species and contribute to the overall richness of the region Considering the additive effects of other ha1mful factors both biotic and abiotic such as deforestation or reef vandalism by humans it may be difficult to determine the precise role of natural disasters However it is clear that hurricane activity is a vital component in the promotion of competition and succession in these two distinct habitats that allows them to remain so exceptionally diverse References Bythell JC HillisStarr ZM Rogers CS 2000 Local variability but landscape stability in coral reef communities following repeated hurricane impacts Marine Ecology Progress Series Vol 204 p 93100 Gardner TA Cote IM Gill JA Grant A Watkinson AR 2005 Hurricanes and Caribbean coral reefs Impacts recovery patterns and role in longterm decline Ecology 861 174184 Lauri Bob and Gibson Judy 2000 San Diego Natural History Museum September 20m 2005 lt httpwwwoceanoasisorg eldguidemangroveshtmlgt Sherman RE Fahey TJ Martinez P 2001 Hurricane impacts on a mangrove forest in the Dominican republic Damage patterns and early recovery Biotropica 333393408 Tan Ria April 2001 Mangrove Trees Info Fact Sheet September 20m 2005 lthttpwwwnaturiapersgbulohplantsmangroveitreeshtmgt
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