Species abundance, diversity and interactions

Species abundance, diversity and interactionsDr Shuhaida Shuib5.5.2015lecture 1DefinitionsCommunity:Various interacting species living in a defined area (ecosystem)From various taxonomic groups microbes, fungi, plants, animals

Community structure comprise:Number of species Relative species abundance Species diversityWhat is a guild?

Source: http://www.slideshare.net/raiuniversity/b-sc-micro-biotech-biochem-i-es-u-2-ecologyIn 1948, Frank Preston published a seminal paper, "The Commonness, and Rarity, of SpeciesCharacterized distributions of species abundance by lognormal curvesThe concept of species abundance

LOGNORMAL DISTRIBUTION: PRESTONSpecies diversity: FundamentalsTwo factors define species diversity:Species Richness (Margalef)Number of species in the community.Species Evenness (Pielou)Relative abundance of species.

Quantitative Index of Species DiversityShannon Wiener Index s H = -pi logepi i=lH = Value of SW diversity index.Pi = Number of individuals of species/ total number of samples.Loge = natural logarithm of pi.S = Number of species in community.Rank Abundance CurvesRelative abundance and species diversity in a community shown by plotting:Relative abundance of species against Rank in abundance.

Greater evenness indicated by lower slope.Rank Abundance Curves

A steep gradient : low evenness, high ranking species have higher abundances than low ranking species. A shallow gradient indicates high evenness as the abundances of different species are similar.Habitat complexity and heterogeneity Theoretically: Species diversity increases with increasing complexity What is habitat complexity?The presence and arrangement of PHYSICAL structures in spaceFor example:In tropical rainforests: Foliage heightIn coral reefs: Reef structuresIn mangroves: Roots, trees, leavesWhat then, is habitat heterogeneity?Patchiness (irregularity) of complexityEg: A small patch of habitat in a forest may be extremely complex, but can be homogeneous. If it is heterogeneous, the distribution of complex structures will vary over multiple spatial scales (August, P. 1983. The role of habitat complexity and heterogeneity in structuring tropical mammal communities. Ecology. 64 (6): 1495-1507).

Mac Arthur & Mac Arthur 1961: Positive association between bird species diversity and foliage height diversity. More complex habitat offers more potential nichesNiche: Tolerances and requirements defining conditions and resources by individuals/species to survive.Hutchinson (1957): Niche is made up of dimensions therefore the real niche of a species is multidimensional.

Mangroves: Habitat complexity and heterogeneityExample of a complex and heterogeneous habitat with various potential niches: Mangroves.Highly complex physical structures comprising roots (pneumatophores), tree bark, leaves, detritus on floor All create different niches for different animal species to colonizeIn scales of cm to km, the arrangements of these physical structures differ significantly (patchy)

How does complexity affect species abundance and diversity in mangroves?1. Reduced predationThe presence of roots, example Avicennia marina reduces predation. Some predators could not access smaller prey hiding in between narrow root mats. This increases the abundance and diversity of prey hiding in structures in mangroves.2. Protection from harsh conditionsDetrital matter on the forest floor and shade provided by mangrove tree canopy shelter macrofauna (example crabs) from mortality caused by increases in temperature and desiccation. Increased abundance and activity have been found under areas that are sheltered compared with exposed areas.3. Food Mangroves are extreme habitats, macrofauna that forage need to find food in time while avoiding predators and environmental stress. Food particles are trapped in between roots, microbes on surfaces of detritus and algae growing on root structures and trees provide increased availability of different types of food. This can be exploited by different species which may feed on different sources of food.4. ProductivityThe various niches available in mangroves cater to different species, each with specific requirements. Mangroves are highly productive, similar to tropical rainforests despite being categorized as a low nutrient system. This is because the use of resources by each animal is efficient in mangroves all available resources are used and then cycled back internally in a more enriched form to be used by fauna and plants. This is why some species of crabs and molluscs are highly abundant in mangroves.5. Solid foundations The presence of physical structures: provides a solid foundation for the building of animal habitats. Example, crabs have been found to build burrows near roots, so that the sediment does not collapse. Barnacles have been found to colonize the underside of leaves. In one mangrove tree, macrofauna of different species and abundance were found on roots, under leaves, on tree barks and in between detrital matter on the forest floor. Disturbance and diversityGrime (1977): Any process that removes biomass from the community, which significantly influences species coexistence and maintenance of biodiversity Connell (1978) . (Source: Hughes,A.(2010)Disturbance and Diversity: An Ecological Chicken and Egg Problem.Nature Education Knowledge3(10):48))

White and Pickett defined disturbance:Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment.Major characteristics: frequency and intensity

Sousa (1979) : High and low levels of disturbance would reduce diversity, intermediate levels promote higher diversity.

Species diversity is low on small, frequently disturbed boulders, inhabited by: primarily of fast-growing colonizer species;Large boulders are dominated by competitively superior algae, leading to low diversity;Diversity is maximized on intermediate boulders, with a mix of colonizers, competitive dominants, and species that lie in between these two extremes. Source: Hughes,A.(2010)Disturbance and Diversity: An Ecological Chicken and Egg Problem.Nature Education Knowledge3(10):48)TheIntermediate Disturbance Hypothesis(IDH) states that local species diversity is maximized when ecologicaldisturbanceis neither too rare nor too frequent. At high levels ofdisturbance, due to frequent forest fires or human impacts like deforestation, all species are at risk of going extinct.

Source: www.nature.comSpecies: InteractionsSpecies interactions : basis for manyecosystem properties and processessuch as nutrient cycling and food webs. Variability of interactions these interactions: dependent on evolutionary context and environmental conditions. Can be either intra-specific or inter-specific interactions.Intra-specific interactions: interactions that occur between individuals of the same species, Inter-specific interactions: interactions that occur between two or more species

Source: Lang,J.M.&Benbow,M.E.(2013)Species Interactions and Competition.Nature Education Knowledge4(4):8Types of species interactions: Direct interactions: Feeding activities affecting food web structureIndirect interactions: Trophic cascades, indirect commensalism, apparent competitionIndirect CommensalismOne species indirectly benefits another species (through a third species) while it is neither helped or harmedExample: Martinsen, Driebe, Whitham (1998)Beavers fell cottonwood trees which then produce stump sproutsBeetles prefer consuming high nutrition sprout leaves Beetles grow larger, faster and utilize defensive compounds found in leaves Apparent CompetitionNegative effects between two competitors who share a predator or herbivoreOne species may facilitate the presence or increase the abundance of the predator which suppresses the second speciesOrrock, Witter, Reichman (2008)Exotic plant Brassica nigra sheltered mammals which increased herbivory on native bunchgrass Nassella pulchraIndirect Interactions

Therefore, Keystone species exert strong effects on community structure large contribution to ecosystem functions

Negative effects of keystone species loss:

Akeystone speciesis aplantoranimalthat plays a uniqueandcrucialrole in the way anecosystem functions.Increase in several predators/consumers when one keystone predator is removed. The ecosystem cannot support an unlimited number of animals, and the prey will soon compete with each other for food and water resources.Failure of reproduction and recruitment of certain plantsNew plants or animals could also come into the habitat and push out thenative species.Loss of a modifier (ecosystem engineer) results in loss structure/materials affecting energy flow and resources.

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