Lecture 6 - Landscape Ecology - PDF

LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH HABITAT FRAGMENTATION HABITAT FRAGMENTATION: the process during which a large expanse of habitat is transformed into a number of smaller patches of smaller total area isolated from each other by a matrix of habitats unlike the original...

LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH HABITAT FRAGMENTATION HABITAT FRAGMENTATION: the process during which a large expanse of habitat is transformed into a number of smaller patches of smaller total area isolated from each other by a matrix of habitats unlike the original ○ Naturally fragmented into small populations (think many lakes) ○ But human activities such as mining, logging,urbanization can cause habitat fragmentation Human impacts have caused larg continuous habits to be fragmented causing: ○ Total amount of habitat decreases ○ Number of patches increases ○ Average patch size decreases ○ Amount of edge habitat increases ○ Patch isolation increases ○ Each patch can support lower populations Real populations are affected by random chance ○ DEMOGRAPHIC STOCHASTICITY: random variation in both birth and death rate due to differences in individuals ○ ENVIRONEMNTAL STOCHASTICITY: random variation in birth and death rates due to changes in environmental conditions CORRIDORS CORRIDORS: small strips of habitat that increase connectivity between habitat fragments ○ Facilitate movement, allowing patches to remain occupies ○ Increased gene flow and genetic diversity ○ Corridors most important for organisms that require a a continuous connection to move between patches (e.g., non flying) Corridors can have negative impacts too! They can facilitate the movement of predators, competitors and pathogens of your conservation target species! WHAT IS A METAPOPULATION METAPOPULATION: a large population that is broken up into small, isolated patches, called subpopulations, that are connected by infrequent dispersion MODELING METAPOPULATION DYNAMICS At equilibrium, how do you calculate the proportion of occupied patches? LEVIN’S METAPOPULATION MODEL ASSUMPTIONS Births and deaths constant (so we can ignore) Subpopulations exist in two states: occupied or empty Only occupied patches produce dispersing individuals LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH Dispersing individuals equally likely to disperse into occupied or empty patches All patches equally accessible to dispersing individuals Empty patches get colonized, based on proportion occupied patches. Patches go extinct at constant rate, e (independent of proportion occupied patches) IMPLICATIONS Patches that are not currently occupied by a species are not necessarily unsuitable for that species. Should conserve both occupied habitat and unoccupied suitable habitat! Removing unoccupied patches will decrease the number of occupied patches at equilibrium! THEORY OF ISLAND BIOGEOGRAPHY Not all patches are created equally: patch size is important! Generally, larger patches support larger populations. ○ *Larger populations have lower extinction rates! Richness increases with patch size, because of lower extinction rate! LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH HOW DOES COLONIZATION RATE VARY WITH ISOLATION More isolated populations have a lower probability of colonization (less dispersal)! Lots of observations, but very hard to do manipulative experiments to test impacts of patch area and isolation on richness EQUILIBRIUM THEORY OF ISLAND BIOGRAPHY The number of species on an island reflects a balance between the colonization of new species and the extinction of existing species Due to limited resources/available niches, the rate of colonization of new species declines as the number of species on the island increases More species on island, more likely species are to go extinct due to sheer numbers as well as increased species interactions (e.g. competition) ←Due to limited resources/available niches, the rate of colonization of new species declines as the number of species on the island increases More species on island, more likely species are to go extinct due to sheer numbers as well as increased species interactions (e.g. competition) → LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH LECTURE 6 - LANDSCAPE ECOLOGY SEPTEMBER 30TH