Lecture 3 Flashcards
What are the patterns of island biogeography?
. Large islands have more species than small islands (not just actual islands but fragmentation’s)
. Near islands have more species than far islands
What are the processes (immigration rate, extinction rate) island biogeography?
. The further the island the slower the immigration rate
. Extinction rate is higher on small islands
When is immigration rate higher?
If there aren’t many species
When will extinction rate be increased?
When there is more species/ more competition for resources
When is the number of species stable?
When the equilibrium between immigration rate of new species and the extinction rate of species is reached
What are the types of islands? Give examples
. Oceanic islands (volcanic origin) e.g. Seychelles, Lord Howe Island group
. Land-bridge islands (sea levels have changed at some point) e.g. Britain
. Habitat islands e.g. forest patches surrounded by farmland
What is a metapopulation?
A set of local populations occupying various habitat patches and are connected to one another by the movement of individuals among them (a group of populations that are linked)
Describe the classical metapopulation (island) model
. In this model, population persistence requires an adequate rate of migration
. Small populations are extinction-prone but are sufficiently close to neighbouring populations for recolonisation (so if one goes extinct there will be immigration)
. There are occupied and unoccupied patches
(Have a few habitats/ islands that are occupied and there is exchange between them)
Describe the Mainland-island metapopulation (island) model
. A system of patches or subpopulations located near a larger mainland patch or subpopulation
. Dispersers from the mainland can reach each of the small patches or subpopulations
. It is assumed the mainland population does not go extinct, therefore neither does the metapopulation
Describe the patchy metapopulation (island) model
. All subpopulations are sufficiently (all on the same island) close to migrate between subpopulations, so subpopulations are not at risk of going extinct
. The subpopulations are not independent, and their demographics are closely linked
. When a subpopulation goes extinct it is not noticed because it is part of a large continuous metapopulation
Describe the non-equilibrium metapopulation (island) model
. Each subpopulation acts as a separate metapopulation (no exchange between them). Each metapopulation is extinction prone because of its isolation and small size
. The subpopulations are completely independent, and their demographics are not linked because of large distances between them
. When a subpopulation goes extinct it does not get recolonised (because it is too far away for others to move in).
Describe what natural boundaries (edges) between habitats are
Ecosystem boundaries can have intermediate transitions, can vary in their severity and can provide unique habitats
Give 3 examples of natural boundaries (edges) between habitats
. Gallery forest, San Pedro River Valley
. Arabuko Sokoke Forest, East Coast, Kenya
. Coastal forests, South Africa
Describe what artificial boundaries (edges) between habitats are
Artificial boundaries vary and include: road-forest, forest plantation (varying ages)- natural forest, cropland- natural forest… (affects different species differently as some species will be happy to move through no others will not)
Give 3 examples of artificial boundaries (edges) between habitats
. Coastal forests, South Africa
. Mount Elgon NP, Kenya
. Malaysian Borneo
Give an example (Latin name) of a species that is a core forest species and so has to live in the middle of the forest and so is at risk from deforestation
Tupaia longipes (type of squirrel)
Give an example (Latin name) of a first species so is happy to move between fragmented habitat so isn’t at much risk from deforestation
Muntiacus muntjak
Explain what ecosystem functioning is, giving an example
The processes the species perform in the habitat/ ecosystem e.g. soil cycling, so you might want to focus on species that have more of an impact on that environment
What is a ‘driver’ species?
A species that has a big effect on the habitat
What is a passenger species?
A species that doesn’t have much of an effect on the habitat
Explain the difference between removing a driver species and a passenger species
Removing drivers causes a cascade effect but loss of the passengers leads to little change in the rest of the ecosystem
What is a keystone species?
A species that has a big effect on the environment (some people think wolves are)
Explain the Rivet-popping hypothesis
All species make a contribution to ecosystem functioning. You can lose some but if you lose too many the ecosystem will have catastrophic declines
Loss of species could lead to catastrophic declines in ecosystem functions as there is large uncertainty about the degree of redundancy and the size of future stresses in ecosystems
What does the insurance hypothesis suggest?
That increasing biodiversity insures ecosystems against declines in their functioning or against increased variability in their functions caused by environmental fluctuations (some species have different functions depending on what other species are present and the environment)
Explain the mechanism for the insurance hypothesis
Compensation among species- different species respond differently to environmental changes, and then environmental change, the contribution of some species to ecosystem processes may decrease while that of others may increase
Explain the Idiosyncratic hypothesis
Ecosystem function changes when diversity changes, but the magnitude and direction of changes are unpredictable, as the roles of species are complex and varied.
Matters in what sequence species are added or removed from that sequence
Explain what ecosystem/ ecological resilience concept is
The capacity of an ecosystem (social-ecological system) to absorb or withstand disturbance/ stresses without shifting to an alternative state and losing function and services- so stays within the same regime, essentially maintaining its structure and functions (how much disturbance an ecosystem can take without changing completely). Threshold- whole habitat changes (might just be part of a nature processes)
Give an example of a regime shift according to the ecological resilience hypothesis
The amazon rainforest- people cutting it down- climate change/ when trees are cut down it becomes dying- causing more forest fires
Explain what a tipping point is
When ecological systems (ecosystems, populations) pass a critical point, their shift from one system to another becomes inevitable
The shift may be to a system with reduced functions (e.g. carbon sequestration of forest versus Savannah)
The shift may be irreversible (e.g. population extinction)
There may be early warning signals
(Change in climate can lead to change in soil do not as simple as replanting the trees)
Explain what an extinction vortex is
The pull toward extinction: The tendency of small populations to decline toward extinction once caught in a downward spiral. External affected or abiotic factors will have a much bigger impact on a small population than a large
When can significant losses of genetic variability occur?
In isolated small populations, particularly those on islands and in fragmented landscapes
Give examples of when species going through bottleneck has caused harm
. Lions in Tanzania went through bottleneck and there were 15 left and compared with a population that had not gone through bottleneck there was a difference in viability so inbreeding depression did cause harm to that population
. Wolves in Scandinavian zoos showed reduced reproduction and survival of adults in these populations
Give an example of a species where there is no evidence that bottlenecking has an effect on the population
. Dwarf mongoose that live in African savannahs there is a lot of inbreeding going on, but no one has managed to measure any affect on the population (so depends on a species as to how much affect bottlenecking will have)
What is a minimum viable population?
The smallest size required for a population or species to have a predetermined probability of persistence for a given length of time (usually about 100 years)
Who proposed the classical island biogeography model?
MacArthur and Wilson (1963)
What does island biogeography suggested the difference between different sized islands are?
Large islands have more species than small islands Near islands (<500 miles from colonisation source) have more species than far islands (>2000 miles from colonisation source)
What does equilibrium on an island mean for the island?
That it is stable
What does edge structure of a forest determine?
The magnitude of change in microclimates and vegetation structure in tropical forest fragments (Didham and Lawton 1999)
What does ensured continued functioning of an ecosystem require?
Actions to focus on functional groups that are represented by only one or two species, i.e. groups in which there is little or no redundancy (the state of being not or no longer needed or useful)
