5. Populations Fluctuate in Abundance Flashcards
What concept is emphasized in literature on the environment and ecology?
balance
What is the reality of most population growth/size?
most populations fluctuate, others have periodic cycles, others have wild fluctuations in numbers
What are examples of populations that fluctuate wildly in numbers?
locusts and ciacadas
What are 2 truths of population fluctuation and extinction?
populations will go extinct at some time → populations, not species
small populations will go extinct more than large populations
What circumstances make it more likely for populations to go extinct?
more variability
less resources
What is the unit of evolution?
populations, a species will only go extinct when the last population does
Why should we analyze populations and not species when looking at extinction?
focusing on species is overly optimistic (because populations can still exist but be suffering)
extinction isn’t a good judge of the health of a species
What are good judges of the health of a species?
the range populations cover, number of individuals in populations
How does population size affect extinction risk?
the smaller the minimum viable population (MVP) the more likely they are to go extinct
MVPs are based on probability so they’re not guaranteed
How do populations persist?
any population will go extinct sooner or later
most populations are not isolated - meta populations! (populations that are linked by movement of individuals)
What is actually the unit of extinction?
meta-populations, should focus on them rather than isolated populations
What are sources and sinks?
sources: produce excess individuals, they’re exported to sinks
sinks: produce too few individuals
(sinks are important in case the source runs out)
What is the rescue effect?
the movement of individuals between sub-populations of a meta-population decreases the chances of extinction
sources stabilize sinks
sources stabilize sources
How does the rescue effect affect extinction?
the more isolated populations the less chance they both go extinct independently, BUT
meta-populations are way, way more likely to survive because they can rely on each other
How do humans affect the rescue effect?
humans fragment the landscape and disrupt the rescue effect
roads make meta-populations harder to facilitate, animals are shy to cross roads usually
