Plant Ecology Lectures PDF

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Lecture notes for lecture 4 and 5 - Plant ecology...

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MODULE 2 – PLANT ECOLOGY Module Overview: Key Vocabulary - Community – group of two or species occupying the same geographical area at the same time - Richness – (species richness) is the number of different species in an ecological community - Rare – rarity is a group of organisms that are very uncommon or scarce - Common – group of organisms that exist in large numbers – regarded as being at low risk of extinction - Succession - is the process of change in the species structure of an ecological community over time. - Decomposition – breaking down and recycling of dead tissue and are converted into nutrients or simpler organic forms - Direct Interaction – deals with the direct impact of one individual on another when not mediated or transmitted through a third individual. - Indirect Interaction - the impact of one organism or species on another that is mediated or transmitted by a third. - Mutualism – interactions between species that has a mutual positive outcome or effects – e.g. reproduction or survival - Commensalism – an association between two organisms in which one benefits and the other derives neither benefit nor harm. - Contramensalism - parasitism and disease. only part of the prey/host is consumed, harmful but not necessarily lethal. pathogens. - Amensalism – association between organisms of two different species in which one is inhibited or destroyed and the other is unaffected. - Competition – the struggle between two organisms for the same resources within an environment. - Neutralism – the relationship between two species that interact but do not affect each other. - Density - the number of individuals of a given species that occurs within a given sample unit or study area

Lecture 4. Week 5 Topics: - Ecological community and its properties - Species richness - Species diversity - Rank-abundance curves - Species composition - Food webs - Community succession

 Communities – an assemblage of species’ populations that occur together in space and time Ecological communities – properties of individual organism (behaviour, physiology), properties of populations (density, sex ratio), properties of communities (richness, diversity)  Species richness – number of species in an area o Sub-sample: species richness estimates for communities depend on number of samples taken o Most common species represented in first few samples o More samples, rarer species discovered  Taxonomy – the science of classification of organisms o Bacteria, Archaea, Eukarya  Species richness and Taxonomy o Taxonomic issue for estimates of species richness in a region  Misidentification of species o In the hypothetical study region, how many species are there?  Antechinus: 4 species o Occupy space from south Australia to tropical Queensland – however each individual species range is small --- IMPORTANCE OF TAXONOMY  Rarity and Commonness o When a community is described only in terms of richness, an important element is ignored o Species are usually in different proportions (e.g. abundances)  Rare species  Common species o Rare and common used in many different contexts  Rarity – spatial occupancy has changed to become contracted from former (subjective)  Wombat distribution – faecal sampling, looked for active burrows (sticky tape – hair type and genetic variants)  Rare Species – classed as rare, smaller range, instability in numbers  Common Species  Over-abundant species – e.g. Undaria pinnatifida, Threskiornis Molucca  Species diversity - Important to include the rarity and commonness of species when describing ecological communities o Example: Same richness, different diversities  Simpson’s diversity index  Diversity and spatial scale: Alpha diversity, beta diversity and gamma diversity  Rank-abundance curves o A single number (index) is limited in describing community structure o Solution? o Looks at the number of times sampled, and then ranks the most common species to most rare – helps understand range o Community structure o Models: Broken stick, Log-normal, Log series, Geometrical series  Species composition o Species presence – the actual species comprising the community  E.g. the community contained Acacia falcata, Jacksonia scoparia, Persoonia linearis

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o Contribution (abundance) of each plant species to the community  E.g. Acacia falcata (58 individuals), Jacksonia scoparia (22 individuals), Persoonia linearis (10 individuals) Food webs o A food web is a summary of the feeding relationships within a community o The earliest work on food webs concentrated on simplified communities o 3D relationships, constantly evolving Community succession o Ecological Maxims: Evolution matters, time matters and space matters o Succession: A process of replacement over time of one community by another o Non seasonal, directional and continuous pattern of colonisation and extinction on a site by populations of species  Species richness and abundance change over time  Conditions, resources and other species vary through time Primary succession: o A temporal succession of species on an exposed landform that has not previously been influenced by a community  Lava flows from volcanoes  Craters from meteors  Substrate after glacial retreat Secondary succession: o Succession in an area where vestiges if a previous community are still present  Vegetation partially removed by:  Fire, storm, human activities, abandonment of farmland  Fire is an important factor that has influenced the evolution of the Australian flora and fauna o The effects of wildfires on small mammals in heathland communities o Initially, fires markedly reduce communities if small mammals o Changes in the distribution and abundance of mammal species after fire are strongly related to habitat requirements. Mammal succession: Mus domesticus o Mammals emerge after different times Degradative succession o Temporal succession of species that occurs on a degradable resource o Short periods of time o Degradation uses up some resources, making other available o Environmental conditions shift over time o Ends when the resource is completely metabolized and mineralized o Any packet of dead organic matter is exploited by decomposers and detritivores o Different species invade and disappear in turn Decomposition o Arrivals – over time of decomposition  Blow flies  Flesh flies  Ants (Muscidae)  Ants (Formicidae)  True flies (Piophilidae)  True flies (Fanniidae)

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Coleoptera – beetles Sepsidae

Lecture 5, Week 6  Species Interactions I Contents: - Direct vs Indirect Species Interactions - Direct Species Interactions - Mutualism - Commensalism - Contramensalism - Amensalism - Competition - Neutralism  Ecological Maxims: Life would be impossible without species interactions – all species are dependent on one-another for energy, nutrients and habitat  Direct and Indirect Species interactions  Direct species interactions: The direct impact of one individual on another when not mediated or transmitted through a third individual  Why do we care about species interactions? o Global declines in biodiversity have stimulated much research into the consequences of species loss for ecosystems and the goods and services they provide. o We don’t know much about how species loss will affect communities o Keystone species: species who have large impacts on the ecosystems they live in, comparative to other species – e.g. Tasmanian Devil  Direct species interactions o There are six main types of direct effects which are classified by the net effect of the relationship on each individual: positive, negative, or neutral o Dependent on biotic and abiotic factors  Intraspecific VS Interspecific interactions o Intraspecific – within species o Interspecific – between or among species  Mutualism o Facilitative, or positive, interactions are encounters between organisms that benefit at least one of the participants and cause harm to neither o Mutualism: Both species derive benefit (+,+) e.g. bees and flowers o Positive interactions occur when one organism makes the local environment more favourable for another either directly (i.e. shading or baffling) o Ecosystem engineering: can be viewed as a mutualistic interaction – e.g. kelp o E.g. Tree shrews and pitcher plants – Borneo = poop in plant \  Obligate vs Facultative Mutualism

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o Obligate mutualism – interaction is required to persist e.g. leaf cutter ants o Facultative Mutualism – interaction is not required to persist e.g. clown fish and sea anemones Commensalism (+, 0) o When one organism is positively affected by the relationship while the other organism is not affected, either negatively or positively, by the interaction o E.g. Barnacles and Whales o How do we test it? o Study: Looked at the development of agricultural societies  adapted  sedentary, human commensal = identified genes previously linked to a high starch diet – sparrows Contramensalism (+, -) o Positive self-effects for species 2; no positive self-effects for species 1 o Includes: Predation, Herbivory, Parasitism Predation o Predation takes place when one organism (the predator) consumes another (the prey) o Lotka-Volterra predator prey model = measures predation o Specialist predators occur in:  All vertebrate groups  Many invertebrates  Fungi  Plants Predation and co-evolution o Co-evolution: Two species  Consistent interactions  Gene pool changes o Essentially an “arms race” e.g. Moth and Bat Parasitism o Parasitism: a parasite consumes only part of ‘host’ organism and effects are not always lethal o Obligate Parasite: Restricted to one host species; dependent for fitness. Host = environment o Facultative Parasite: Does not entirely rely on host for fitness o Micro vs microparasites o E.g. Protozoan parasite – Toxoplasma gondii  Blood parasite introduced via cats o Endemic parasites = adapted to each other o Enzooic disease = chronic o Epizootic disease o Epidemic disease = short term impact (host), Major and fatal diseases

 Amensalism (0, -) o One individual is negatively affected by interaction with another individual who is not affected by the relationship i.e. penicillium o Hard to observe, e.g. Tadpole and Eucalyptus leaves o Measure o Cyanobacteria-dominant soil crusts in Australia’s semi-arid rangelands  Competition (-, -)

o Competition occurs when two organisms compete for the same resource (food, space, mates…) o Both individuals are negatively impacted by competition for the resource due to either:  Resource is limited  Or interference o Interspecific competition: For resources  selective force driving ecological character displacement o Measure? o Is competition important in natural systems? o Lab experiments – relevant to natural systems? o Patterns in nature attributed to competition often reassessed as being caused by other processes o Evidence of competition is best revealed by carefully planned field experiments  Neutralism (0, 0) o Interactions between the two individuals are neutral in regard to both species o Lactobacillus and Streptococcus o True neutralism is probably rare in nature o Coexistence?  Competitive Exclusion Principle o Gause’s Law: No two species can occupy the same niche  Competition would be too intense o Humans  outcompeting other species o  Competing related species often evolve distinguishing characteristics in areas where they both coexist  Competition and Niche o Fundamental vs realised niche o Fundamental: all the environmental conditions where a species is able to live o Realised: where the species actually lives...