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Lecture 31
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biological community – an assemblage of populations of various species living close
enough for potential interaction
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a carrier crab carrying a sea urchin on its back for protection
interspecific interactions – relationships between species in a community
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§ these species often cannot coexist in the same environment
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o herbivory (+/-) – an herbivore eating a plant
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tick)
§ mutualism (+/+) – both species benefit
• obligate – one species can’t survive without the other
• facultative – both species can survive alone
§ commensalism (+/0) – one species benefits and none are harmed
o facilitation (+/+) or (+/0) – species interactions that benefit at least one participant
and harm neither
ecological niche – the sum of a species’ use of biotic and abiotic resources
o “ecological role”
o ecologically similar species can coexist in a community if there are one or more
significant differences in their niches
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resource partitioning – differentiation of ecological niches, enabling similar species to
coexist in a community
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prey display various defensive adaptations:
o behavioral
o morphological
o mechanical
o chemical
mimicry can also be used by predators to approach prey

Lecture 32
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species diversity – the variety of organisms that make up the community
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A, B, C are the species
p is the relative abundance of each species
ln is the natural log

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communities with higher diversity:
o more productive; more biomass – the total mass of all organisms
o more stable in productivity
o better able to withstand and recover from environmental stresses
o more resistant to invasive species – organisms that become established outside of
their native range
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o ex
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adding pike to a Finnish Lake to control roach populations that were
overeating zooplankton and causing the formation algae blooms
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Yellowstone National Park
intermediate disturbance hypothesis – moderate levels of disturbance can foster greater
diversity than either high or low levels of disturbance
o high levels exclude many slow-growing species
o low levels allow dominant species to exclude less competitive species
ecological succession – the sequence of a community changes after a disturbance
o primary succession – occurs where no soil exists when succession begins
o early-arriving linked with later-arriving:
§ early arrivals may facilitate the appearance of a later species by making
the environment favorable
§ they may inhibit the establishment of later species
§ they may tolerate later species, but have no impact on their establishment
o secondary succession – begins in an area where soil remains after a disturbance
§ ex
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𝑆 = 𝑐𝐴3
# of species

how many species should be
found as habitat area increases
area

constant
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species richness on islands depends on:
o island size
o distance from the mainland
o immigration
o extinction
pathogens – disease-causing microorganisms, viruses, viroids, and prions
o zoonotic pathogens – transferred from other animals to humans
o vector – an intermediate species in the transfer of pathogens

Lecture 36
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conservation biology – seeks to preserve life
o several fields:
§ ecology
§ physiology
§ molecular biology
§ genetics
§ evolutionary biology
biodiversity has three main components:
o genetic diversity
o species diversity
§ endangered species – in danger of becoming extinct throughout all or a
significant portion of its range
§ threatened species – likely to become endangered in the foreseeable
future
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acid rain
ecosystem services – encompass all the processes through which natural ecosystems and
their species help sustain human life
o purification of air and water
o detoxification and decomposition of wastes
o cycling of nutrients
o moderation of weather extremes

Lecture 37
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species recovery may be possible with cloning technology
biologists focusing on conservation at the population and species levels follow two main
approaches:
o small-population approach – studies processes that can make small populations
become extinct
§ prone to inbreeding and genetic drift which draw it down in an extinction
vortex
§ minimum viable population (MVP) – minimum population size at which
species can survive
§ effective population size – based on populations breeding potential
𝑁5 =

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4𝑁7 𝑁8
𝑁79 𝑁8

# of
effective
males
# of
population
females
size
o declining-population approach – focuses on threatened and endangered
populations that show a downward trend, regardless of population size
§ steps:
• confirm the population is in decline
• study the species’ natural history
• develop hypotheses for all possible causes of decline
• test the hypotheses in order of likeliness
• apply the results of the diagnosis to manage for recovery
managing habitat for one species may have positive or negative effects on the other
species

Lecture 38
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conservation biology has attempted to sustain the biodiversity of entire communities,
ecosystems, and landscapes
ecosystem management is part of landscape ecology which seeks to make biodiversity
conservation part of land-use planning
edges or boundaries between ecosystems are defining features of landscapes
o and edge has its own set of physical conditions which differ from those on either
side of it
movement corridor – a narrow strip of habitat connecting otherwise isolated patches
o promotes dispersal
o helps sustain populations
o in areas of heavy human use, artificial corridors are sometimes constructed
biodiversity hot spot – a relatively small area with a great concentration of endemic
species and many endangered and threatened species
o good choices for nature reserves
o can change with climate change
nature reserves – biodiversity islands in a sea of habitat degraded by human activity
zoned reserves – include relatively undisturbed areas and the modified areas that
surround them and serve as buffer zones
urban ecology – examines organisms and their environment in urban settings
o ex
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o accumulation of toxins
§ biological magnification – concentrates toxins at higher trophic levels
where biomass is lower
• PCBs and many pesticides
• pharmaceutical drugs enter freshwater through human sewage and
agricultural runoff
o climate change
§ greenhouse gases - gas in an atmosphere that absorbs and emits radiation
within the thermal infrared range
§ greenhouse effect - 𝐶𝑂< , water vapor, and other greenhouse gases reflect
infrared radiation back toward Earth
§ many organisms may not be able to survive rapid climate change
§ assisted migration – the translocation of a species to a favorable habitat
beyond its native range
§ solutions:
• reducing energy needs
• converting to renewable sources of energy
• stabilizing 𝐶𝑂< emissions
• reduced deforestation
o ozone depletion
§ Earth is protected from damaging effects of UV radiation by a layer of
ozone molecules in the atmosphere
§ chlorofluorocarbons (CFCs) produced by human activity are destroying
atmospheric ozone
§ causes DNA damage in plants and poorer phytoplankton growth

Lecture 40
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sustainable development – development that meets the needs of people today without
limiting the ability of future generations to meet their needs
Sustainable Biosphere Initiative
o define and acquire basic ecological information for responsible development,
management, and conservation of Earth’s resources

A – tertiary consumer
B – producer
C – primary consumer
D–
E – carnivore/secondary consumer



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