| Are species rich communities more stable than species poor communities? | Empirical and theoretical studies show that increased richness makes the community more stable at the ecosystem level but less stable at species level.
Increasing diversity stabilizes ecosystem functioning. Having multiple species in a plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations. |
| Are species rich communities more stable than species poor communities? | Empirical and theoretical studies show that increased richness makes the community more stable at the ecosystem level but less stable at species level.
Increasing diversity stabilizes ecosystem functioning. Having multiple species in a plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations. |
| Parasitism | The parasite obtains nutrients from one or a few host individuals. It causes no harm, death is not caused immediately. They are widespread and are important regulators of their host pop. |
| Ecological effects of parasites | Affect the fitness of their host: Survival, reproduction and substantial energy cost to fight off infections.
Manipulate their host to enhance parasite survival, reproduction and transmission. It can affect the abundance and distribution of the host. |
| Types of life cycle | Direct, Intermediate host, transmission by a vector, brood parasitism (in birds), parasitoids (larvae develop, eat host) |
| There are outcomes for the host when it is attacked by a parasite | Susceptibility: continuum of responses. Virulence: Continuum of responses from being killed |
| Outcomes for the parasite | Response of host has a direct effect on parasite's fitness. The host can: grow, spread the parasite and actively fight the infection |
| Disease dynamics and cycles. | Basic reproductive number: R0=SxβL
S= # suscepribles in a pop
β= transmission rate
L= average time to become infectious. |
| Importance of co-evolution of host and parasite | Coupled pops dynamics of both host and parasite works to maintain existence of both pops. |
| The Red Queen Hypothesis | Co-evolutionary dynamics in which the host and parasite struggle forever with no long term reduction in extinction probability. The parasite is more likely to evolve more rapidly than the host. |
| Virulence and fitness | Virulence: The damage caused to a host. A parasite affects host's fitness by: using host's resources to grow and reproduce. The parasite increases its fitness the same way + manipulating host's behaviour to increase transmission. |
| Three phases to parasite evolution | Phase 1: Accidental infection. Virulence does not follow evolutionary principles, rare and less virulent than established infections
Phase 2: Evolution of virulence after infection
Phase 3. Evolution of optimal virulence |
| The Trade-off Hypothesis | 1. NS favours traits in transmission 2. Increase replication, increase transmission and increase mortality 3. transmission. reproduction and virulence is constrained by mortality. |
| Zombie Fungi | Ophiocordyceps unilateralis – a fungal pathogen of forest ants Camponotus leonardi in Thailand. This ant lives in the forest canopy.
1. Fungal spores germinate on the insect cuticle and grow into the haemocoel.
2. The fungus grows into ant heads, near the brain.
3. The ant behaviour is modified to a stereotypical pattern |
| Zombie Fungi (pt. 2) | 1. Infected ants descend from canopy nests to understory vegetation. 2. Show repeated convulsions that
make them fall down and stop them climbing back up to the canopy. 3. Bite into abaxial leaf veins before
dying. Get locked onto plants. 4. Ants die in patches 25cm above soil surface, where conditions for parasite development are optimal 5. Spores are released from dead ants to continue the fungus life cycle. |
| Mutualism = reciprocal exploitation | A relationship between 2 species in which there is a net benefit for both parties. It involves direct exchange of goods and services eg plants and microbes |
| Endozoochory | Seed dispersal via ingestion by animals. Animal pollination more effective than passive pollination. |
| Pollination : competition & conflicts | Plants competing with each other for pollinators. Pollinators compete with each other for flowers. Evolution: greater rewards from plants to pollinators and the development of specialized flower structures. But mutual exploitation: plant exploits pollinator, pollinator exploits the plant. |
| Mycorrhizas and Three main types | Hyphal network created by the mycorrhiza captures mineral nutrients (P, N) and water from the soil. Given to the plant in exchange for C. Can also protect against disease. Arbuscular Mycorrhizas (AM), Ectomycorrhizas and Ericoid Mycorrhizas (6k species, form sheath around roots, in forests ). |
| Fixation of atmospheric N | N is limiting in many environments. Rhizobia – bacteria fix N in root nodules of leguminous plants. Where nitrate is limiting in soil, legumes can obtain competitive advantage. |
| What determines species richness | R - range of available ecosystem resources
n - niche breadth
o - niche overlap |
| Factors affecting species richness (SR) | 1. Geographic factors: Latitude, physical disturbance, isolation. 2. Biotic factors: Predation increases SR by predator-mediated co-existence. Competitive exclusion can reduce SR. 3. Climatic Variations: seasonality, niche specialization, more resources exploited. 4. Island Biogeorgaphy: SR decreases as area decreases. |
| Why are lower latitudes more diverse? | Environmental characteristics: Energy availability, Age, Harshness, Productivity. Potential Evapotranspiration (PET): amount of water which would evaporate or be transpired from a saturated surface |
| “Paradox of enrichment” | Species richness declines with productivity. Competitive exclusion could provide an explanation. |
| Equilibrium Theory of Island Biogeography | Predictions: Number of species on an island becomes constant through time. Continual turnover of species due to immigration and extinction. Large islands support more species than small islands. |
| Intermediate disturbance hypothesis | Disturbance maintains an intermediate successional stage, potentially enhancing species richness. Prevents competitive exclusion from developing. |
| Why does richness affect function? | 3 Hypothesis: Complementarity – niche differentiation permits greater use of available resources. Facilitation – some species have positive effects on the ecosystem role played by others. Sampling Effect – increased function due to increased likelihood of encountering a particularly productive or competitive species. |
| Threats to Biodiversity | Habitat loss, degradation and fragmentation. Invasive alien species. Pollution. Overexploitation of resources. Global environmental change. |
| Ecological Genetics | A study of fitness related traits and underlying genetic loci in natural pops. Offers insights into: Molecular ecology, co-evolution, local adaptation, extended phenotypes. |
| Molecular Ecology | Uses molecular genetic techniques to investigate ecology, evolution, behaviour and conservation. It may address: population structure and phylogeography, conservation genetics, speciation genetics, ecological interactions. |
| Tools for Molecular Ecology | Restriction Enzymes. PCR. SSR markers: Highly polymorphic, reproducible, co-dominant, have multiple alleles, seq. tagged. SNP markers: Most abundant class, 4 possible variants at each locus. |
| Markers and Technology Development | Next Generation Sequencing: Whole genome sequencing, resequencing, genotyping by sequencing. Helps us understand species boundaries and pop differentiation, estimate migration rates, track reproductive success. |
| Population Genomics | Uses data from multiple loci in different populations to infer those underpinning adaptive traits and to identify outlier loci. |
| Regulation and determination of abundance | Regulation: tendency for population to return to a certain level if it is above / below it because of density
dependent processes. But precise abundance will be determined by combined effects of all factors and all processes affecting a population. |
| Four different patterns of long term population dynamics in nature | 1. Phases of pop growth after disasters. 2. Dynamics are controlled by the env carrying capacity k= high 3. Same as 2 but k=low 4. Habitable sites are dominated by pop decay after sudden episodes of colonization. |
| Foundation species (kelp forests) | The “bedrock” of a community. Usually primary producers. Highly abundant or have large biomass. Modify the environment to produce habitats that benefit other organisms. |
| Keystone species | Influence community structure disproportionately to their numbers. Function in a significant manner through
their activities. Their removal changes community structure and leads to loss of diversity. |
| Keystone species engineers | Autogenic engineers: Modify the environment by modifying themselves. Modify the environment by modifying themselves. Top predators.
Allogenic engineers: mechanically change living or non-living materials from one form to another. |
| “Trophic cascades” | An action at one trophic level will propagate through the food chain. This influences community structure and
composition. |
| “Bottom up” | Nutrient availability controls plant numbers. This controls herbivore numbers. Which controls predator numbers. Test by adding fertilizer to an ecosystem. |
| “Top down” | Predators reduce herbivores. Which results in an increase in plant abundance. Test by removing predators to an ecosystem. Top down manipulations propagate down the food chain very strongly in most ecosystems. |
| “Top down” wins | An analysis of 121 community studies that: Added fertilizers to ecosystems, Removed predators. Nutrient availability affects plant abundance and diversity: But bottom up manipulations do not propagate up the food chain in most ecosystems. |
| Grazing interaction | Interaction of predation (grazer) and competition; grazing increases plant species richness, Reduce plant densities so comp is not intense (inferior comp. increased). No grazers: Completely superior species dominate |
| Response of a community to disturbance | Resilience: The speed with which a community returns to its former state after a perturbation.
Resistance: The ability of the community to avoid displacement in the first place. |
| Are species rich communities more stable than species poor communities? | Empirical and theoretical studies show that increased richness makes the community more stable at the ecosystem level but less stable at species level.
Increasing diversity stabilizes ecosystem functioning. Having multiple species in a plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations. |
