Blog Post Week 1
Elizabeth Chambers
Full citations: Gouezo, M. et al. 2019, “Drivers of recovery and reassembly of coral reef communities.” Proc. R. Soc. B 286: 20182908.
http://dx.doi.org/10.1098/rspb.2018.2908
http://dx.doi.org/10.1098/rspb.2018.2908
Clements, F. E., “Nature and Structure of the Climax.” Journal of Ecology, Vol. 24 No. 1 (Feb. 1936), p. 252-284.
https://www.jstor.org/stable/2256278
https://www.jstor.org/stable/2256278
Lead Author Background:
Frederic Clements was a plant ecologist who worked extensively in studying plant community ecology and the nature of succession in plants. He obtained a doctorate from the University of Nebraska and taught at the University of Nebraska and University of Minnesota before moving to the Carnegie Institute in Washington, D.C. He was key in introducing the idea of an ecological climax as the result of successional change in ecological systems.
The recent paper’s lead author, Marine Gouezo, holds a Master’s in Marine Conservation and currently conducts research at the Palau International Coral Reef Center, which is associated with the Khaled bin Sultan Living Oceans Foundation. In addition to this paper, she has published four other papers dealing with the topic of coral reef ecology and was lead author on one such paper. Ms. Gouezo’s research concentrates on studying the dynamics of populations of corals growing in the Western Pacific Ocean, focusing largely on the Palau island group located in Micronesia.
Paper Background:
As outlined in Clements (1936), ecological systems in a climax community state have reached a point of stability, or a steady state equilibrium. He notes that this concept had been introduced in the decades prior to this paper, and seeks to outline the specific details and mechanisms of succession and climax. He explains that over time changes occur through the process of succession and the community shifts and changes until it reaches a climax—the point of stability where it has the best community make-up for the given climate in which it exists. This equilibrium state can be disturbed by various factors, and disturbances result in the community entering a non-climax stateof disequilibrium. Under Clements’s concept of an ecological climax, when given adequate time to recover, the community will undergo succession and reassemble itself, eventually returning to its steady climax state.
In the case of the coral reefs in Palau that Gouezo et al (2019) studied, a disturbance occurred during the 1998 El Niño event, which caused widespread coral bleaching in the Pacific. The authors studied the reefs of Palau after the bleaching event in order to track the community over time and study the transition from the early successional colonists (in this case, algae) to the climax community reached after the coral had recolonized the area. Because of a lack of previous such studies on reefs combined the difficulty in studying an ecological community type that experiences disturbance so frequently, the authors noted an under-studied area of ecological research and this project aimed to describe the process of recovery in the unique coral reef community.
Methods:
In his 1963 paper, Clements reviews the past work he and others have done on climax communities, as well as describing the observations made in the field in various community types across different climate zones. From this compiled data, heexamines the community structures that have been observed anduses that analysis to define numerous terms to describe the characteristics of a climax community as well as to describe thesuccessional stages and stages in the process of climax.
Because coral reefs have been shown to take years to decades to recover, Gouezo et al used a long-term dataset from a survey monitoring Palau starting in 2002 and tracked the recovery and climax until the reefs experienced another disturbance in 2012 in the form of a tycoon hitting the islands.
Using transects of the reef, the authors measured benthic cover, fish abundance, and the density and size of coral. The abundance of parrotfish was used to determine the level of herbivory being experienced. The study included surveys taken from different habitats within the Palau reef area—western and eastern outer reefs, inner reefs, and patch reefs, with each habitat studied at two different depths. To analyze the data, a generalized additive mixed model (GAMM) studying the effect of time, depth, and habitat on the community was utilized. The authors defined stability as occurring when the GAMM did not show statistically significant differences in coral coverage between two or more time points. An instantaneous growth rate (IGR) calculation was used to study the recovery of each major coral group.
Results:
Clements describes numerous classifications of stages in the process of succession and climax. He defines a climax as “a more or less permanent and final stage of a particular succession and hence one characteristic of a restricted area” (p. 253), that is: climax communities represent the stable end-point of succession. He identifies the species with the greatest abundance and greatest influence on the community as the “dominants.” Relatedly, he defines the subdominants as being highly important species in their communities but with less of an influence than the truly dominant species. He uses plants in determining both the dominant and subdominant species in a given system and categorizes climax communities based on their dominants. The term “influents” is used to refer to animal species having an important impact on the communities, though Clements does not stress the impact of animals as much as he does for the influence of plants.
In addition to climax itself, Clements identifies proclimax as a community at a sort of potential climax state which has some, but not all, characteristics of a true climax community and which may gradually undergo succession and become replaced by a true climax over time. The proclimax classification is further separated into four distinct types: subclimax, disclimax, preclimax and postclimax. He defines subclimax as the period in succession when the community is nearing climax but has not yet reached it—it is a prolonged slast successional stage before climax has been reached. In order to account for the effect of humans on an ecological system, Clements introduces the term disclimax, which is a stable man-made community. In the case of disclimax the community is at a steady state that has been reached because of the influence of humans and/or their domestic animals rather than being any equilibrium that would be reached in nature. Preclimax refers to a stable community with organisms ‘lower’ than those that would be expected in a climax, and postclimax refers to a stable community with organisms ‘higher’ than what would be expected. Additionally, he defines a panclimax as two or more related climaxes with similar features, and eoclimax as an ancestral climax. He determines that the eoclimaxes formed the modern biome zones seen on earth.
In Gouezo et al, the study period began three years after the major bleaching event and at this starting point, the outer reefs both had moderate coral cover, inner reefs had high cover, and patch reefs had low cover. The western outer reefs reached a climax in 2010, indicated by a lack of statistical difference in years beyond 2010. At this point, an equilibrium had been reached and the community returned to its climax state. Similarly, the patch reefs and inner reefs both ceased to show significant differences from year to year from 2007 onwards, indicated that they had also reached a stable ecological climax. In the eastern outer reefs, the population dynamic continued to change and did not show stabilization occurring and therefore had not reached a climax.
Of the coral taxa studied, Montipora had the greatest IGR and had a positive response to higher levels of wave exposure. Acropora IGR had the greatest positive effect with higher levels of larva and juveniles and had a negative response to greater wave exposure. The Porites IGR exhibited a negative response to algal cover.
Summary of the Discussion:
Clements’s paper outlines in detail the path that communities take toward reaching a stable equilibrium. In a given undisturbed community system, succession will gradually occur and the system will reach a climax point. Deviations from this climax result when a system is still in the process of succession and has not yet reached the climax or as the results of a disruption altering the community away from its climax state. When left undisturbed from natural disaster, human influence, or other disruption, Clements argues that a given community will follow a reliable trajectory of succession, eventually reaching an ‘end point’ at the climax state and will remain at this equilibrium indefinitely until disruption does occur.
The authors of the 2019 paper determined that it is possible for coral reefs to reach and remain at a stable climax state and that shallow-water reef communities like that of Palau require a minimum time span of 9-12 years to recover from bleaching events and return to their climax community states and that the reefs will remain stable and abundant in coral when they are free from disturbances. They stress the importance in taking into account the ability of coral communities to achieve reaching a steady climax community state and the need to take this into account when studying coral recovery. Because climate change increases the frequency and severity of major weather events, they warn that it will be increasingly difficult for reefs to return to a climax state following disturbance.
The authors noted a number of different factors affecting the recovery of coral reefs post-disturbance. The IGR data indicated that recruitment values, or the number of new individuals in a population, were important for recovery, as shown by the positive effect that higher larval and juvenile densities had on Acropora corals. Algal cover reduced the amount of coral growth as the two organisms were forced to compete for available substrate on which to grow. This interspecificcompetition effect was mediated by the parrotfish, which are herbivores that consume algae and thus reduce competition for substrate for corals. The effect of wave exposure varied depending on the specific coral taxa.
Thoughts and Comments:
I found the discussion section highlighting Guezo et al’sfindings of a stable climax to be interesting. The authors note that reefs are frequently called “disturbance-driven systems” implying that disturbances are a normal part of reef ecology, but despite this they can still reach a steady state. This opens up interesting possibilities for further long-term studies of coral communities in other areas investigating the community dynamics and their abilities to reach a climax.
Clements’s paper did seem largely theoretical for modern ecology given the increasing level of disturbance and human impact on ecological communities; however, the indication of coral reefs reaching a climax state indicates that the ideas from Clements’s work are not entirely theoretical and that it is possible for a community to go without disturbance for a long enough period to actually reach a climax.
The Gouezo article is an interesting complement to the Clements paper because of the settings in which each observed climax communities. Clements studied strictly terrestrial communities and noted that "plants constitute the fixed matrix of the biome in direct connection with the climate" (p. 254). The corals in Gouezo’s study had functionally the same type of ecological role in their marine setting. In both the terrestrial and the marine settings, the stability of the community was determined by the amount of the dominant species (plants and corals, respectively).
ReplyDeleteAlthough Clements provided a detailed overview of succession states and achieving a climax community, I think Gouezo was accurate in her assessment that “there is no universal theory that encompasses all concepts” of succession and community recovery (p. 8). Gouezo’s statement also seems to align with Elizabeth’s comment that Clements’s paper is “largely theoretical for modern ecology.” Clements provides a framework for understanding succession and climax communities, but given the increased frequency of anthropogenic ecological disturbances, his original ideas may need to be rounded out with additional support from more recent studies of modern ecosystems.
Clement used a lot of detailed classification to describe different climax stage (subclimax, preclimax, postclimax, and disclimax) along the succession and different groups within a given communities (e.g. association, faciation, consociation, etc) that can reflect the species composition. I think sometimes the margins of these climax are not quite clear. For example, since climax describes an “equilibrium stage”, then community A (preclimax) wouldn’t change into community B (postclimax) until environmental factors change, which overlaps the definition of disclimax. For example, a shrubland communities could be a postclimax to a grassland due to climate change (increased precipitation) or the human control of natural fire.
ReplyDeleteThe coral reef paper studies the community climax in a less known environment. Like the author discussed in the paper, coral reefs are “disturbance-driven environment” and they still have steady state. In my opinion, this resembles the “subclimax” described by Clement, as the coral reef is ongoing to the “real climax” but periodically disturbed by waves and winds. The author also mentioned the significant loss of corals caused by El Nino, and it took a long period to recover. However, I think it is difficult to discriminate “climax” and “disclimax” for coral communities, compared with terrestrial ecosystems.
The Gouezo paper fits well with the Clements paper, highlighting how the concept of ecological climax has progressed since Clements discussed the idea in the 1930s. Interestingly, Clements focuses primarily on plants, defining "climax" as only referring to plants and "biome" as referring to both plants and animals. He mentions that this is because plants are "fixed" and connected only to the climate, while animals are connected to both climate and plants (as consumers). In the paper by Gouezo et al., it seems that the corals act as the "plants" in Clements paper in that they are fixed, although they are not the primary producers in coral reefs. It would be interesting to follow the re-assembly the primary consumers in coral reefs, such as phytoplankton and algae, following disturbance.
ReplyDeleteAnother piece of Clements' paper that stood out to me was this statement, "Man alone can destroy the stability of the climax during the long period of control by its climate". Exactly this is happening in reef systems now. Climate change is stressing ecosystems with strengthened typhoons, ocean acidification, and warmer temperatures. Climate change is partially what motivated the recent study by Gouezo. It seems that understanding climax stages and ecological succession is more important than ever, given the massive ecological shifts we are currently experiencing and expect to see in the future.
While these papers do fit well together, there are distinct differences. The one that caught my attention was something we mentioned in class on Wednesday. Clements is very focused on stability, what that looks like, and how it is reached. He also views stability as the default stage that systems infrequently stray from. Gouezo, like many modern ecologists, is very aware that all systems exist in a dynamic and changing world.
ReplyDeleteI find Clements's idea of plant communities being super organisms interesting in light of recent research. While Gleason's individualistic community idea has been more accepted in recent history, Clements core idea also hold some truth. We are now aware of microbiomes and vast below ground fungal networks that in a way create a super organism.
Not sure why its doesn't show my name. This comment was made by Miranda Salsbery
DeleteThe papers definitely compliment each other, yet accomplish different goals. Clements' (1963) paper lays down a foundation, and mainly focuses around defining terminology he and other scientists used at the time. I am unsure how much of the defined terminology are used today. For example, distinctions between "climax" and "sere" confuse me a bit. As I was reading, I was thinking back to previous ecology papers I have read (all written from 1980 onwards). I have not seen a distinction like this before and was wondering if terms such as these are used more when discussing flora rather than fauna. I claim to know very little about how plants and plant communities are studied, so perhaps some to of the terminology in this paper (e.g. dominant, influent, proclimax, etc.) are still used today but only in this field? Regardless of this, Clements (1963) paper is a good source of information on succession in different biomes (a biome being the end result of a climax after succession has occurred as I took it from this paper).
ReplyDeleteOn the other hands, Gouezo et al. (2019) is an excellent recent paper that discusses coral colonization after a major disturbance event. The study, unlike the Clements (1963) paper includes both models and statistical tests to determine multivariate interactions between organisms and environmental effects. Animals (specifically invertebrates involved in reef composition) were the primary focus of this study, although the effect of algae on coral recolonization was also taken in account. Interestingly enough, this paper provided a number of years needed for coral reefs to recolonize without disturbance (i.e. 9-12 years). This differed from the Clements (1963) paper where succession and biome formation appeared to be discussed in longer stretches of time (i.e. thousands to millions of years). The models used the in the Gouezo et al. (2019) demonstrate the refinement of new ecological techniques when discussing succession events.
Huh, mine also excluded my name. This post was written by Kat Jordan.
DeleteI thought that Clements (1936) was interesting in a historical sense, but it didn’t seem particularly relevant to how people currently study the dynamics of ecological communities. It seems that the language and conceptual framing of modern studies (e.g., Gouezo et al. 2019) draws more from the C. S. Hollings’ work on alternative stable states and resilience. To me, the major difference between modern ecological thought and Clements’ views is the modern recognition of alternative stable states and thinking about the duration and path of transients which differs from Clements’ insistence that there was a “true climax” that existed for communities in specific climates without disturbance. The Gouezo et al. study is an excellent illustration of modern thought, e.g., their statement that the recovered coral communities may be different than the pre-bleaching communities (alternative states), in their visualization of the time-parameterized trajectories of the recovering coral communities (fig. 4), and their demonstration that coral dominated communities could persist even in the face of disturbance.
ReplyDeleteThe comment in Gouezo et al. that “the time needed for community re-assembly is habitat specific and drivers of recovery are taxa specific” made me wonder if there are possible generalizations that could be made about recovery. For instance, could we make generalizations about recovery time from knowledge about the generation times and/or dispersal rates of species in recovering communities?
Something that I didn’t notice in either papers is the potential challenges in distinguishing between transients and equilibria. I don’t know if long transients (see Hastings et al. 2018) would happen/are relevant to the coral systems considered by Gouezo et al., but I do think that recognizing the possibility of long transients may be important in studies of how communities respond to disturbance.
- David
While I was reading the Clements paper, one fundamental question kept coming back into my mind: under the current and largely human-driven climate change scenario, can plant communities (and really, ecosystems) today ever return to a “steady climax state”? I found his discussion of the interactions between the preclimax-climax-postclimax vegetative transitions to be very fascinating, but I think the scale of human-caused disturbances today (e.g., large-scale deforestation, infrastructure building and development, mining) is much larger than it was in 1936 and may significantly impact how long (if, at all) it takes for communities to reach a new stable climax post-disturbance. Thinking about the rates of habitat/biodiversity loss, the anticipated human population growth, and the continued pace of urban development, it seems that the majority of terrestrial plant communities might not be able to transition out of the sub-climax stage as they recover following a disturbance. In other words, the climate-driven transition back to historical vegetative climaxes that Clements discusses may not be possible in the current epoch of climate change.
ReplyDeleteNevertheless, the framework that Clements introduced for thinking about shifting community structure and succession was useful as a reference when reading about the recolonization and regrowth of coral reefs in the Gouezo manuscript. I was surprised to learn that the time-scale for succession to the climax state for reef communities can occur in only 9-12 years post-disturbance; coming from a terrestrial plants background, I am used to thinking about community succession happening gradually over much longer periods. I thought that the article was very well-written overall and included informative figures that helped reinforce my understanding, particularly the conceptual model (Figure 1) and the temporal dynamics within each of the reef communities (Figure 3). Additionally, Gouezo et al. did a good job of combining ecological theory with robust, quantitative data-driven modeling to contextualize and support their conclusions.
This was posted by Bailey McNichol - sorry I forgot to include my name!
DeleteI think that current theory about community assembly encompasses more of the complex interactions in a system than Clements' (1936) foundational paper on the climax. I admit that I may be biased as someone with interest and background in animal ecology and little to no experience with plant ecology, but I questioned Clements' notion that animals play lesser roles in defining a community assembly (p. 66). This seems contradictory with what I have read about community structure, especially in classic examples of trophic cascades (e.g., Estes et al. 1998). However, Clements did briefly acknowledge that mammals play an important role in climaxes and that events such as mass migration could change the stage of the climax. Still, I thought it was strange that Clements only mentioned mammals in passing and completely disregarded other animal clades. I was pleased that Gouezo et al. applied the same basal theory to a system that is largely dominated by animal forms because it expanded on Clements' work in a way that both complemented and transformed the original theory.
ReplyDeleteOn another note, according to Clements' climax theory, communities return to a steady state after disturbance except in the case of the disclimax. I wonder how arbitrary it is to define the disclimax, considering that many ecologists now generally regard communities as dynamic and adaptable. This disclimax concept seems synonymous with the idea of a pristine ecosystem, in that we assume a single steady state of the system and manage systems with the goal that it returns to that state. Likewise, Gouezo et al. (2019) orient the recovery of the coral reefs to a previous state, and I wonder how realistic it is that the system will return to that state or if it will need to change and adapt to new conditions. For example, will the coral populations be replaced by a new dominant species?
-Annie
Clements (1936) is a fascinating window into how culture influences science. The culture at the time Clements was working would still have been heavily infused by an authoritarian form of religion, especially the idea that there exists a kind of predetermined “natural order.” This is evident in Clements singular focus on each biome having a singular equilibrial climax state, and the dynamic interactions between plants, animals, and climate constituting a deviation from that equilibrium. I found it particularly fascinating that he reached these conclusions in part by considering the North American Great Plains, which as we now know are extremely dependent upon fire and herbivores to maintain their grassy vegetation. Otherwise, they undergo woody encroachment and become juniper woodlands. Clements, in contrast to seeing herbivores and fire as essential aspects of maintaining a grassy biome, sees them as disrupting the climax state:
ReplyDelete“The general habit of migration among the animals further insured that serious effects from overgrazing and trampling were but local or transitory, while the influence of fires set by the Indians was even less significant in modifying the plant cover.”
In contrast, as others have noted (I particularly like David’s take), Gouezo et al (2019) take a much more modern approach and emphasize the likelihood of alternative stable states in their system. I think alternative stable states are one of the most fascinating things to think about in ecology, and indeed one of the most challenging from a conservation and communication perspective. Gouezo et al.’s finding of how long a coral reef might take to reacquire a given structure demonstrates the challenges inherent to making informed management decisions in an increasingly dynamic environment.
-Lyndsie