Plant Communities PDF

PLANT COMMUNITIES 01/21/2025 SRZ AND QAMMIL  COMMUNITY An Association of Interacting Species Inhabiting Some-Defined Area. Ecologists may study the plant community on a mountainside, along a riverside, below a big gap or small ones, or afte...

PLANT COMMUNITIES 01/21/2025 SRZ AND QAMMIL  COMMUNITY An Association of Interacting Species Inhabiting Some-Defined Area. Ecologists may study the plant community on a mountainside, along a riverside, below a big gap or small ones, or after deforestation.  Communities generally consist of many species that potentially interact in all of the ways 01/21/2025 SRZ AND QAMMIL Community ecologists seek to understand how various abiotic and biotic aspects of the environment influence the structure of communities.  Community structure includes attributes such as the number of species, the relative abundance of species, and the kinds of species comprising a community. 01/21/2025 SRZ AND QAMMIL 01/21/2025 SRZ AND QAMMIL After Gap formation-Plant Community 01/21/2025 SRZ AND QAMMIL 01/21/2025 SRZ AND QAMMIL  Species Abundance Most species are moderately abundant; few are very abundant or extremely rare. The relative abundance of species is one of the most fundamental aspects of community structure. 01/21/2025 SRZ AND QAMMIL 01/21/2025 SRZ AND QAMMIL Notice that few species were represented by more than 8% cover or less than 0.15% cover. Most species had intermediate coverage. Distributions, are approximately "bell-shaped" or "normal. Since abundance is plotted on a log scale, Preston's curves are called "lognormal" distributions. 01/21/2025 SRZ AND QAMMIL  Species Diversity  Definition : A combination of the number of species and their relative abundance.  Species diversity Define on the basis of two factors:  (l) the number of species in the community which ecologists usually call species richness, and  (2) the relative abundance of species, or species evenness.  The influence of species richness on community diversity is clear.  A community with 20 species is obviously less diverse than one with 8001/21/2025 species SRZ AND QAMMIL ~Species diversity is higher in complex environments. ~ Intermediate levels of disturbance promote higher diversity. 01/21/2025 SRZ AND QAMMIL Species diversity Index - Shannon-Wiener index  s  H′ = －∑ p log p i e i  i =1  where:  H' = the value of the Shannon-Wiener diversity index  P = the proportion of the ith species i  loge = the natural logarithm of Pi  s = the number of species in the community  The minimum value of H' is 0, which is the value of H' for a community with a single species, and increases as species richness and species evenness increase. 01/21/2025 SRZ AND QAMMIL  Species diversity is higher in complex environments  How does environmental structure affect species diversity?  InGeneral, species diversity increases with environmental complexity or heterogeneity.  An aspect of environmental structure important to one group of organisms may not have a positive influence on another group.  Must know something about the ecological requirements of species to predict how environmental structure affects their diversity.  Must know something about their Niches. 01/21/2025 Stature of vegetation and number of warbler species Forest Complexity and Bird Species Diversity 01/21/2025 SRZ AND QAMMIL  The number of warbler species at the study sites increased with forest stature.  The study sites with greater volume of vegetation above 6 m supported more warbler species.  In other words, MacArthur found that warbler diversity increased as the stature of the vegetation increased.  These results formed the foundation of later studies of how foliage height diversity influences bird species diversity.  01/21/2025 SRZ AND QAMMIL  MacArthur was one of the first ecologists to quantify the relationship between species diversity and environmental heterogeneity.  Quantified the diversity of species and the complexity of the environment using the Shannon- Wiener index, H'.  Measured environmental complexity as foliage height diversity, which increased with the number of vegetative layers and with an even distribution of vegetative biomass among three vertical layers, 0 to 0.6 m, 0.6 to 7.6 m, and > 7.6 m.  MacArthur's foliage height diversity, like species diversity, increases with richness (the number of vegetative layers) and evenness (how evenly vegetative biomass is distributed among layers). 01/21/2025 SRZ AND QAMMIL Foliage height diversity and bird species diversity. 01/21/2025 SRZ AND QAMMIL Variation in vegetation along a gradient of soil and moisture conditions 01/21/2025 SRZ AND QAMMIL Fertilization and plant diversity at Rothamsted, England. 01/21/2025 SRZ AND QAMMIL  What does increasing nutrient availability have to do with environmental complexity?  Increasing nutrient availability, whether due to natural variation or fertilization, reduces the number of limiting nutrients.  Eventually, when or where all nutrients are abundant, light remains as the single limiting resource.  Under these conditions the algal or plant species most effective at competing for light will dominate the community and species diversity will decline.  Increasednutrient availability correlates with reduced algal and plant diversity. 01/21/2025 SRZ AND QAMMIL