Ecology 2 Flashcards
Sigmoidal population growth curve
Population growth can’t be limitless – carrying capacity is the maximum population size that environment can support, it varies with abundance of limiting resources (water, space for breeding, food or territory for obtaining food and dissolved oxygen in water for animals and water, light, soil nitrogen and phosphorous for plants)
Factors that contribute to the change in population size – natality/mortality and immigration/emigration
Exponential growth phase – ideal environment (unlimited resources), little diseases, few predators, high natality and immigration (greater than mortality and emigration). Transitional phase – lack of resources, increased competition and mortality, natality still larger than mortality but less so than in exponential. Stabilization at the plateau phase (carrying capacity reached)
Limiting factor classification and their effect
- Density independent limiting factors – the same effect whatever the population size and they cause population sizes to fluctuate – e.g. population of plants not adapted to low T, frost kills them all – draught, wild fire, volcanic eruptions, hurricane, deforestation
- Density dependent limiting factors – have an increasing effect as population becomes larger, basis for negative feedback mechanism – they tend to bring pop size back to carrying capacity – three groups:
a) Competition (water, food, light)
b) Predation (pop of prey denser and easier to find)
c) Infectious disease, parasitism and pest infestation (increase with pop density because the transfer of pathogens, parasites and pests from host to host is easier if the hosts are closer together)
Intraspecific relationships and their examples
Competition and cooperation – exist between individuals of the same species and usually within the same population:
Competition exists unless a resource is abundant (natural selection): Duckweed and light, Gannets and nest sites, Creosote bushes and water (desert), Waxwings and berries on trees
Cooperation: Emperor penguin males huddle together, Chimpanzees hunt in groups, Mackerel swim in tightly packed, Elder duck parents take turns to care for groups of offspring
Interspecific relationships
Exist between individuals of different species, two categories:
1. Between species not living in close association:
a. Herbivory – primary consumers feed on producers
b. Predation – one consumer species kills and eats another consumer species
c. Interspecific competition – two or more species use the same resource
2. Between species living in close association:
a. Mutualism – both species benefiting from the association
b. Pathogenicity – one species lives inside another and causes disease in the host
c. Parasitism – one species lives in or on another species and obtains food from them, the host is harmed and the parasite benefits
Examples of mutualism/symbiosis
- Rhizobium bacteria and Fabaceae (legume) plant roots, bacteria fix N2 and convert it to NH4+ (enriching the soil with N-compounds) so plants use them to create proteins, the plant provides the bacteria with sugar
- Hard coral cells and Zooxanthellae algae, obtain shelter and light exposure while corals obtain energy/food through Zooxanthellae photosynthesis
- Fungal hyphae (Mycorrhizae) and orchid plant roots – hyphae act as an extension of plant roots, fungus obtains sugar from photosynthesis
When are alien species invasive?
When the limiting factors (density-dependent factors) of the habitat don’t limit their population growth and when they outcompete the endemic species (complete exclusion) – extensive eradication programs requires
Solve using Chi squared test
Fucus serratus and Fucus vesiculosus present together 2 times, Fucus serratus only present 1 time Fucus vesiculosus present only 3 times, neither present 0 times
Contingency table
E – expected frequency – calculated assuming independent distribution, calculated by formula:
Row total x column total / grand total (number of quadrats with one or another algal species/total no of quadrats)
Chi-squared value (X2) tells us how likely it is that H0 is correct, formula: (observed-expected)squared over the expected
p value = critical value
Assumption made – the degree of freedom is the number of different outcomes minus one – the significance level can be different, depending on how precise our measurement should be, acceptable percentage of chance events is usually p=0.05
Antibiotic and allelopathic agents – explain and provide example for each
They are secondary metabolites – products of metabolism that are not vital for growth/life but are essential for interaction with the environment (outcompeting rivals and protection)
Antibiotics secreted by microorganisms to kill, inhibit or prevent the growth of other species of microorganisms – Penicillium fungi are saprotrophic, compete with bacteria for food, penicillin interferes with peptidoglycan cell wall of Gram-positive bacteria
Allelopathic agents secreted into the soil by plants to kill or deter the growth or neighboring plants – Tree of heaven is invasive in North America, releases ailanthorne and inhibits germination, growth and survival of other tree species for up to 5 m from the trunk
Flow of matter and E in an ecosystem
Ecosystem = open system, matter gets recycled in closed systems, 60% of energy lost as heat
Food chain and web
- diagram that shows transfer of E in a (partial) ecosystem
- a more accurate and complete diagram (illustrates the feeding relationships among species within a community, reveals species interactions and community structure, one species can have multiple trophic levels in the same food web)
Producer -> primary consumer -> secondary consumer -> tertiary consumer -> all get decomposed by decomposers which bring back the nutrients back to producers that use them together with sun and water to produce C-compounds
Arrows show the direction of E flow
E loss in ecosystems – how does this affect the population density of apex predators
An average of 10% remains when E is transferred from one trophic level to another (the effectiveness of transfer varies between 5-20%, depends on the ecosystem, only one percent of UV radiation can be absorbed for photosynthesis) – lost as heat (through CR), E in form of nondigestible or non-edible parts of the producer’s/primary consumer’s body
(Apex) predators are the rarest, this is the biological law – their population size is controlled because they need the most E to maintain themselves (doesn’t apply to humans)
Control of populations in communities
Top down – overhunting, disease (animal viruses) – an increase in predator numbers will decrease the number of prey in lower trophic levels
Bottom up – temperature, pH of soil, available nutrients – reduce producer population size and thus population sizes of all consumers
How is dead organic matter generated?
- Death of whole organisms
- Defecation (removal of feces from the gut)
- Shedding of leaves, skin cells, hairs, arthropod exoskeletons (molting) and other unwanted body parts
Role of decomposers
Saprotrophic organisms and bacteria are decomposers because they break down insoluble macromolecules into small soluble molecules and ions (gradual breakdown of solid structures) – they return the nutrients to the ecosystem (provide other organisms with a constant supply of nutrients)
Autotrophs – types and mechanisms of production
Reduction reactions turn simple inorganic C sources into an initial C-compound (C fixation). E for further anabolic processes is obtained by light or chem E (substrate in reduced state and oxidize them, oxidation releases E). Chemiosmosis – excited electron accepted to chains of electron carriers in the plasma membrane of the bacterium, E is released – reduced NAD and ATP used to fix CO2
Assimilation
the process of absorbing C compounds and making them part of the body
Four main forms of E loss from food chains:
- Incomplete consumption – E in dead organisms passes to detritus-feeders and saprotrophs
- Incomplete digestion – indigestible material egested in feces and E passed to saprotrophs – detritus
- Cell respiration – CO2 and H2O from C-compounds – do not pass to next trophic level – also results in a loss of C compounds and therefore biomass in every trophic level (60% of E lost in each organism)
- Heat loss – E transfers never completely efficient (because E is lost, it cannot be recycled) – due to CR
Why don’t organisms in higher trophic levels need to eat a greater mass of food to gain enough E?
Connect this to how food chains are limited.
Because biomass is also lost between trophic levels – more energy contained in less mass in organisms in higher levels
Food chains are limited in length because of E loss – not enough remains to support another trophic level (max four or five) – animals in higher levels do not need to eat more food to gain enough E (prey contains large amounts of E per unit of mass), there is just not a lot of prey available
Energy pyramid
shows the amount of E stored at a specific trophic level (represented by level width) and the amount of E transferred between the levels. Width of bars is proportional to the amount of E per meter squared of area occupied by a community per year (kJ/m^2y)
Production – two types of production
accumulation of C compounds in biomass, both autotrophs and heterotrophs produce biomass by growth and reproduction:
1. Primary production (autotrophs), mass of C compounds is synthesized from CO2 and inorganic substances
2. Secondary production includes obtaining C compounds from organisms in lover trophic levels which results in an increase in biomass – secondary production is lower than primary and it declines with each successive trophic level
