Conservation Bio Exam 3: Reserve Design

making reserves as circular in shape as possible

minimizes edge effects

perimeter of a circle is much … than a square

less

do locations that are near multiple edges experience more intense edge effects than areas that are near a single edge

yes

example of edge effect intensity vs number of edges

fletcher’s study on bobolink (B. oryzivorus)

fletcher’s study on bobolink (B. oryzivorus)

the probability of bobolink occurrence was significantly lower in plots with multiple edges compared to a single edge

areas near multple edges experience significantly

more intense negative edge effects than areas near a single edge

soft edge

habitat fragment edge in which the difference in species composition, vegetation cover and abiotic conditions between the fragment and the neighboring patch are small

hard edge

habitat edge in which the differences in species composition, vegetation cover and abiotic conditions between the fragment and the neighboring patch are large

buffer zones create

“soft edges” around habitats to shield wildlife from harsh edge effects while allowing for sustainable human activities

buffer zones definition

managed areas that surround protected habitats to shield them from negative impacts

community

assemblage of species that occupy the same place at the same time

equilibrium model

interactions among the species that co-occur in a community determine the species composition of the community; community composition remains stable over time

non-equilibrium model

community composition is unstable over time because most communities are typically recovering recurring disturbances; disturbance regime, not abiotic interactions, is most important in determining species composition

disturbance

any unpredictable event that removes biomass from a community

disturbance regime

characteristics of the disturbances that is typical for a particular ecological community; includes type, frequency, intensity, and spatial extent of disturbance

examples of how communities can have the same type of disturbance, but very different disturbance regimes

taiga: large, deadly, rare fires coastal savanna: small, less intense, and frequent fires

landscape fire mosaic

quilt-like pattern of vegetation patches across a landscape that have burned at different times, frequencies, or intensities

succession

orderly natural progression of communities following a disturbance

primary succession

succession that occurs after a disturbance that removes the soil

secondary succession

succession that occurs after a disturbance that leaves the soil in-tact

traditional linear model of succession in forests of eastern North America

disturbance, lichens+annuals, larger perennials, coniferous trees, oaks+hickories, beech+maple (climax)

three hypotheses for the nature of interactions between early-successional and late-successional species

facilitation, inhibition, and tolerance

facilitation

early-successional species modify the ecosystem in a way that makes establishment of later-successional species possible

inhibition

early-successional species impede the establishment of later-successional species. Later successional species establish when earlier successional species start to die, releasing the inhibition

tolerance

there is minimal effect of early-successional species on later-successional species. Earlier-successional species are “early” because they can disperse to disturbed sites more quickly

revisions to the traditional linear model of ecological succession

arrested (cyclic) succession and alternate stable states

arrested (cyclic) succession

repeated disturbance that occur with a frequency less than the time required for a community to reach its theoretical climax produce a stable mid-successional community composition OR cause community to cycle through early and mid successional stages

alternate stable states

for an individual site, there is more than one stable community composition; which state is present may reflect events early in succession or perturbations that drive one stable community to another

many savannas are examples of

arrested succession

example of a community that depends on arrested succession due to repeated fires

black-capped vireo

why does the black-capped vireo depend on arrested succession

needs low, dense, ground-level shrubs for nesting, which naturally disappear as a habitat matures into a tall, open forest.