A community consists of mainly 3 groups. Seasonal periodicity — temperature, rainfall and photoperiod determine the reproductive cycle of its inhabitants. Dial periodicity — animals of terrestrial community active during the day and inactive during night. Even within permanent and stable community, fluctuations in species abundance and numbers occur due to the interplay of biotic potential and environmental resistance. Environmental stability is the fluctuations in the abiotic factors of the ecosystem.
Both the types of stability are closely related. The structure of community has a major role in determining the degree of environmental variability. For e. A community is a self-sustained unit. It is the development of a community. Primary succession is the series of community changes which occur on an entirely new habitat.
A community is an aggregate of organisms, which form a distinct ecological unit. The size of community unit may be large forest community or small community of invertebrates.
Different community occurs in different habitats. The composition and character of a community is an indicator of the type of environment that is present. The structure of a community is dependent on: 1 the number of species. Species diversity indices give quantitative expression of community structure. Communities are constantly changing. The replacement of one community by another is called community succession. The final stage in community succession is a climax community.
On the whole a community is considered as a highly integrated self-contained organic unit. A biocoenosis is a biotic community, coined by Karl Mobius in Community concept is one of the most important principles in Ecology. Gleason American Ecologist , This hypothesis depicted a community as a chance assemblage of species found in an area because they have similar abiotic requirements.
The interactive hypothesis was proposed by F. Clements in Communities are stable, integrated, and orderly entities. Biologically they have a highlypredictable composition. The diversity and abundance of a species in a particular community will be the same before and after a disturbance. Communities develop by passing through a series of predictable stages, culminating in a stable climax community.
Communities are neither stable nor predictable. Plant and animal communities are ephemeral associations of species that just happen to share similar climatic requirements. It is largely a matter of chance whether a similar community develops in the same area after a disturbance occurs. Temperatures and rainfall are high and variation is low.
Plants grow all year long. High productivity, and high amounts of aboveground biomass. Extraordinary structural diversity. A multilayered tree canopy is intermingled with vines, epiphytes, shrubs and herbs. This abundance of moisture allows trees to dominate the landscape.
Plants experience a seasonal period of dormancy. Productivity higher than deserts or grasslands, lower than tropical forests. Biodiversity is moderate. Grasslands These areas are also called prairies or steppes. They are interdependent for food supplies and form a specific group. Species diversity affects the stability and productivity of communities.
A latitudinal gradient of species diversity exists for many taxa. Species diversity declines as latitude increases. High diversity in the tropics leads to high productivity. Diversity is positively correlated with stability. Each community type experiences a characteristic type, frequency, and severity of disturbance. Primary Community succession succession Secondary succession It takes place in barren areas It takes place in disturbed areas Forest Succession Pioneer Comm.
Climax Comm. Increase in Species composition And species diversity Increase in species density And heterogeneity Increase in Organic nutrients Metabolic stability in Community metabolism The species may be a strong interactor or a weak interactor. Strong interactors are fewer in number and critical to the ecosystem function.
Elimination of a keystone species may result in the loss of many other species in a community. Invasive species are non-indigenous species whose introduction can cause harm to the community and the environment.
An edge is where two or more different vegetational communities meet. Victor is a highly experienced postgraduate professor, retired from the reputed educational institution - St. He was the dean of sciences, assistant controller of examinations and coordinator several academic research workshops. He has more than 32 years of teaching and research experience He has taught a diversity of courses and published 45 research articles in reputed national and international journals.
Send your comments to : bonfiliusvictor gmail. Total views 18, On Slideshare 0. From embeds 0. Number of embeds 5. Downloads 0. Shares 0. Comments 0. Likes The most parsimonious model, according to the AICc criteria, was the model without any taxonomic component for all processes but litter decomposition Table 1. Then, we examined whether each of the three biodiversity components added a significant contribution to the explanation of ecosystem processes using generalized likelihood-ratio tests comparing nested models.
Conversely, functional identity and functional diversity added a significant contribution for, respectively, 3 and 5 processes. We found that all variance inflation factors were lower than the critical heuristic value of 10 suggesting that collinearity among explanatory variables did not strongly affect our results see Table S2 for values by predictor.
For each ecosystem process, we performed a multiple regression including the 8 indices as predictive variables with a backward procedure to select the minimal adequate model Table 2. In other words, the aggregated mean position of the community within functional trait space in combination with functional divergence accurately predicts the level of ecosystem multifunctionality.
A Multifunctionality performance against functional divergence FDiv. Circle sizes are proportional to performance of communities. See Table 1 for associated statistics. In the high functioning community a , all the dominant species are specialists i. Community a also has a higher mean value on the first PCoA axis of all communities indicated by the black triangle in Figure 3a. Conversely, the low functioning community b has a lower functional divergence value with some dominant species being generalists i.
This community has also a lower mean value on the first PCoA axis. Two 8-species communities of our experiment with the highest multifunctionality level a and the lowest b.
Positions of species are presented in the functional space first and third PCoA axes. The sizes of grey circles are proportional to species relative abundances. Full species names and trait values can be found in Table S1.
Using a structural equation model SEM for ecosystem multifunctionality models for other processes are provided in Text S2 , we confirm that taxonomic composition of communities had no direct significant influence on ecosystem multifunctionality Figure 4 ; only functional identity through first and third PCoA axes and functional divergence had a significant direct effect with functional divergence having the greatest influence positive.
Taxonomic diversity did have a significant influence on the functional structure of communities, but the greatest effect was the positive influence of species richness on functional richness, which had no significant effect on multifunctionality.
Functional indices were weakly related between each other and only two correlations were significant and positive functional divergence and first PCoA axis, functional richness and second PCoA axis. The SEM illustrates that despite the co-linearity between the first PCoA axis and functional divergence, both indices had significant independent effects on multifunctionality.
Numbers next to unidirectional arrows are standardized slopes and those next to bidirectional arrows are correlations. For detailed statistics and for each process, see Text S2. Our results demonstrate that biodiversity components differ greatly in their influence on ecosystem processes.
The taxonomic component, after removing the effects of functional identity and diversity, has no additional effect on processes with consistently low and non significant likelihood-ratio values Table 1. In addition, species richness and evenness were rarely retained in the minimal adequate model Table 2 or by the SEM Figure 4 for their direct influence on ecosystem processes Text S2.
This result can be partly explained by the positive relationship between functional richness and species richness Figure 4 [40] since communities with more species are more likely to hold a higher diversity of traits and thus perform more functions [47].
Therefore, the additional effect of species richness is likely to be weak after removing the effect of functional richness. Similarly, species evenness has no significant influence on ecosystem processes except litter decomposition but it influences the functional structure of communities as revealed by the SEM analysis Figure 4.
We conclude that while the influence of taxonomic structure on ecosystem processes is less important than that of functional identity and diversity, taxonomic composition mediates functional structure. This implies that the taxonomic composition of communities may have indirect effects on ecosystem processes since they are not their proximate, but partly their ultimate, drivers. While it remains difficult to provide a definite mechanistic explanation for the relationship between functional structure and multifunctionality, existing literature and our own observations may provide some clues.
Two of the key functional traits for explaining multifunctionality were leaf phenology evergreen vs. There is only very little evidence that increased phenological complementarity can have a positive effect on annual productivity in early successional forb communities, although such an effect might be stronger at low levels of species richness [48].
Evergreen species at our site might have some photosynthetic activity during mild winter days, but biomass production is very low until the onset of spring. Some of the evergreen or partly evergreen species, however, shown an early onset of growth in spring with an early peak in the season e.
Alopecurus pratensis , Plantago lanceolata , while the summergreen species have a tendency to peak later in the year e. Centaurea jacea , Geranium pratense. Thus, this temporal complementarity of growth might have induced higher productivity with higher functional divergence in leaf phenology.
Variability in leaf inclination is known to enhance the photosynthetic light capture of individual tree crowns e. In our model plant community, the influence of functional divergence on productivity may be due to temporal and spatial partitioning in light capture via complementarity in phenology and leaf inclination, respectively.
In a previous study on the same site, it has been shown that increasing functional diversity positively influences decomposition rates of plant litter, while species richness had no such effect [31]. These results suggest that this positive effect of functional diversity was due to improved microenvironmental conditions for decomposer fauna, and due to higher litter quality. With reference to functional identity, increasing dominance of species with more horizontal leaf inclination might enhance productivity by increasing total light capture relative to communities dominated by species with vertical inclination, which might partially explain the influence of PC1 on multifunctionality.
Supporting this mechanism, communities dominated by forb species with horizontal leaf inclination also had higher leaf area index than those dominated by grasses with a more vertical inclination.
In addition, all nitrogen-fixing legumes planted show a horizontal leaf inclination, partly confounding leaf inclination with N-fixation, the latter being known to positively influence productivity at our site [51]. However, it is unclear how aggregate mean phenology would affect multifunctionality. Perhaps summergreen species are able to grow faster since decreased leaf longevity is associated with increased photosynthetic rates [52]. Short lived leaves also have traits associated with more rapid decomposition rates e.
The higher nutrient content of summergreen leaves is supported by the negative relationship between PC3 and the amount of nitrogen in biomass in the minimal adequate regression. The predominance of variables linked to the functional structure of communities over taxonomic variables in predicting ecosystem processes is in accordance with the most recent findings obtained in experiments [20] or with empirical data [9]. Except for decomposition, we show that functional identity and diversity bring independent and additional explanatory power to ecosystem processes with consistently high likelihood-ratio values.
Overall, the results suggest that neither functional identity nor functional divergence was more important than the other in explaining ecosystem processes and particularly the multifunctionality. So, contrary to other studies, demonstrating the higher contribution of one component over the others [20] , [53] , we demonstrate that this differential contribution may depend on the process involved, and when considering multiple processes the magnitude of the two component effects is similar.
Thus, to reach high levels of predictability in modelling multiple ecosystem processes, functional identity and diversity components have to be taken into account in a common framework [54].
It has been suggested that, since different species often influence different functions, the level of biodiversity needed to sustain multifunctionality in ecosystems is higher than previously thought [15] , [16]. By integrating across four ecosystem processes in assessing the level of community multifunctionality, we show that both functional divergence and functional identity have a predominant role, while species richness has no direct effects Table 2 and few indirect effects Figure 4.
We suggest that this absence of a species richness effect is partly explained by the relatively high richness values considered in our study 4 to 16 species while past evidence for positive effects of species richness on ecosystem processes have often been due to the weak performances of monocultures or very species poor communities [2].
Indeed our results are not in contradiction with previous studies demonstrating positive species diversity effects on ecosystem functioning. Rather, they suggest that, except at the extreme low end of species richness gradients, the taxonomic structure of ecological communities is no longer the main driver of ecosystem processes, with the functional structure being the primary determinant. Our study reconciles two hypotheses that have been alternatively suggested to primarily underpin ecosystem processes: the complementarity and the mass ratio hypotheses.
We suggest that a combined effect of functional identity and functional divergence is the most parsimonious explanation for key ecosystem processes. Taken separately, each biodiversity component has weak explanatory power for ecosystem functioning [20] , [31] , [36].
Our finding is crucial since recent work has demonstrated that global gradients in decomposition rates, for example, are primarily driven by plant functional traits rather than climate [27] , emphasizing the need for better understanding of the interplay between functional structure of communities and ecosystem functioning. The predominance of functional divergence effects on most of ecosystem processes sheds light on the need to preserve specialist species sensu Elton i.
However, since under the combined influence of habitat degradation or global change, we are increasingly losing local specialist species [55] , [56] , the level of functional diversity held by communities is declining worldwide [57]. Our results show that modifying the functional structure of communities has a strong impact on ecosystem processes and should receive more attention in assessing and countering the global decline of biodiversity.
We are grateful to those colleagues that commented on earlier versions of this manuscript, including Michel Loreau, Andy Hector and Eric Garnier.
Conceived and designed the experiments: MSL. Performed the experiments: MSL. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract The accelerating rate of change in biodiversity patterns, mediated by ever increasing human pressures and global warming, demands a better understanding of the relationship between the structure of biological communities and ecosystem functioning BEF. Introduction Ecosystems are facing ever increasing levels of human pressures which imperil the goods and services they provide to humanity.
Ecosystem processes Among the ecological processes that were measured at the German BIODEPTH site we selected those that were relatively independent mean correlation over all selected processes was 0.
Functional traits The selected traits were growth form: caespitosa, reptantia, scandentia, semirosulata and rosulata; leaf size: nanophyllous 20— mm 2 , microphyllous 2—6 cm 2 , submicrophyllous 6—20 cm 2 and mesophyllous 20— cm 2 ; leaf seasonality: summergreen, partly evergreen and evergreen, CN ratio of plant litter [31] ; SLA based on measurements in another biodiversity experiment [38] ; and leaf angle: predominantly vertical leaf orientation, predominantly inclined leaf orientation and predominantly horizontal leaf orientation [38].
Indices for community structure We considered two independent variables related to taxonomic composition: species richness and the evenness of abundance distribution among species using the Pielou index [39].
Download: PPT. Figure 1. Geometrical presentation of functional diversity indices. Statistical analyses In order to disentangle the relative effect of each biodiversity component on ecosystem processes, several alternative nested models were tested.
Table 1. Summary of model comparisons for each ecosystem process as well as multifunctionality. Selection of the minimal adequate model and its explanatory power For each ecosystem process, we performed a multiple regression including the 8 indices as predictive variables with a backward procedure to select the minimal adequate model Table 2.
Figure 2. Relationships between community structure and ecosystem multifunctionality. Figure 3. Two species communities represented in functional space with contrasting multifunctionality levels. Structural Equation Model Using a structural equation model SEM for ecosystem multifunctionality models for other processes are provided in Text S2 , we confirm that taxonomic composition of communities had no direct significant influence on ecosystem multifunctionality Figure 4 ; only functional identity through first and third PCoA axes and functional divergence had a significant direct effect with functional divergence having the greatest influence positive.
Figure 4. Results of the structural equation model SEM linking the multifunctionality of ecosystems to biodiversity indices. Discussion Our results demonstrate that biodiversity components differ greatly in their influence on ecosystem processes.
Supporting Information. Table S1. Table S2. Text S1. Calculation of functional diversity indices. Text S2. Acknowledgments We are grateful to those colleagues that commented on earlier versions of this manuscript, including Michel Loreau, Andy Hector and Eric Garnier. References 1. Science — View Article Google Scholar 2. Ecological Monographs 3— View Article Google Scholar 3. Nature 79— View Article Google Scholar 4. View Article Google Scholar 5. Nature — View Article Google Scholar 6.
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