Ecology: Biodiversity and interspecific
interactions
Part 1: What is ecology…biodiversity and
interactions?
What is ecology?
• Ecology is the scientific study of the interactions between organisms and the environment (interactions determine the
distribution of organisms and their abundance)
Ranges from single organism to entire planet
Even a simple system comprises many (potential) interactions (e.g., on an island with 5 species = 120 interactions)
Few ecological “laws” exist - some general patterns exist, but there are often exceptions (e.g., theory island
biogeography)
Requires an interdisciplinary approach
Study of:
• Life processes, interactions, and adaptations
• The movement of materials and energy through living communities
• The successional development of ecosystems
• Cooperation, competition and predation within and between species
• The abundance, biomass, and distribution of organisms in the context of the environment.
• Patterns of biodiversity and its effect on ecosystem processes
Relevance of ecology:
• An ecological understanding allows prediction and informs management
• development of sustainable fisheries and forestry
• rangeland management (e.g., bush encroachment and stocking rates)
• control of alien species (i.e., invasion biology) and crop pests (i.e., integrated pest management)
• infectious disease management (epidemiology - ecology of diseases)
Species/community richness vs diversity
Diversity = richness + evenness
What is biodiversity?
The term biodiversity (from “biological diversity”) refers to the variety of life on Earth at all its levels, from genes to
ecosystems, and can encompass the evolutionary, ecological, and cultural processes that sustain life.
It has 3 components:
1. Genetic diversity (within and between populations)
2. Species diversity (number, and evenness, of species)
3. Ecological diversity (unique combinations of species and environments)
Abundance vs biomass:
, Interactions between species:
• Relationships between species in a community are inter-specific interactions
• affect the survival and reproduction of each species,
• summarized as positive (+), negative (–), or no effect (0)
Example: A Namaqua rock mouse (Aethomys namaquensis, Muridae) getting dusted with pollen of the Pagoda Lily
(Whiteheadia bifolia, Scilloideae) while lapping nectar at the flowers = pollination
Biotic interactions:
Community Ecology
• A community is a group of populations of different species living in the same area at the same time, that may all
potentially interact
Competition
• Interspecific competition (–/–) occurs when organisms (from different species) compete for a shared limited resource,
with negative consequences for both
• Strong competition can lead to competitive exclusion (i.e., local elimination of a competing species)
= Gause’s competitive exclusion principle:
• two species competing for the same limiting resources cannot coexist in the same place
• an invasive species is an introduced organism that becomes overpopulated and negatively alters its new
environment
Competitive exclusion
An experiment with two species of floating duckweed, which are tiny angiosperms found in ponds and lakes. One species
grows more rapidly in pure culture than the other species. But another has tiny air-filled sacs that enable it to float on the
surface, and when the two species are grown together (3) shades (1) and is the victor in the competition for light.
Predation and herbivory
• Predation (+/–) refers to interaction where one species, the predator, kills and eats the other, the prey
• Herbivory (+/–) refers to an interaction in which an herbivore eats parts of a plant or alga – does not always result in
death
Symbioses
Symbiosis is a relationship where two or more species live in direct and intimate contact
• In parasitism (+/–), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in
the process. Pathogens and parasitoids (+/–) can cause the death of their hosts, while reproducing in their host
• Commensalism (+/0) is where one species benefits, and the other is unaffected (e.g., transport, nesting sites)
• Mutualism (+/+), is an interspecific interaction that benefits both species (e.g., pollination, mycorrhiza, parasite removal,
ants, and acacias)
Facilitation
• Facilitation (+ / +) or (0 / +) occurs when the presence of a species increases the survival and/or reproduction of other
species by changing environmental conditions
Interactions can vary
• Interspecific interactions are not constant
interactions
Part 1: What is ecology…biodiversity and
interactions?
What is ecology?
• Ecology is the scientific study of the interactions between organisms and the environment (interactions determine the
distribution of organisms and their abundance)
Ranges from single organism to entire planet
Even a simple system comprises many (potential) interactions (e.g., on an island with 5 species = 120 interactions)
Few ecological “laws” exist - some general patterns exist, but there are often exceptions (e.g., theory island
biogeography)
Requires an interdisciplinary approach
Study of:
• Life processes, interactions, and adaptations
• The movement of materials and energy through living communities
• The successional development of ecosystems
• Cooperation, competition and predation within and between species
• The abundance, biomass, and distribution of organisms in the context of the environment.
• Patterns of biodiversity and its effect on ecosystem processes
Relevance of ecology:
• An ecological understanding allows prediction and informs management
• development of sustainable fisheries and forestry
• rangeland management (e.g., bush encroachment and stocking rates)
• control of alien species (i.e., invasion biology) and crop pests (i.e., integrated pest management)
• infectious disease management (epidemiology - ecology of diseases)
Species/community richness vs diversity
Diversity = richness + evenness
What is biodiversity?
The term biodiversity (from “biological diversity”) refers to the variety of life on Earth at all its levels, from genes to
ecosystems, and can encompass the evolutionary, ecological, and cultural processes that sustain life.
It has 3 components:
1. Genetic diversity (within and between populations)
2. Species diversity (number, and evenness, of species)
3. Ecological diversity (unique combinations of species and environments)
Abundance vs biomass:
, Interactions between species:
• Relationships between species in a community are inter-specific interactions
• affect the survival and reproduction of each species,
• summarized as positive (+), negative (–), or no effect (0)
Example: A Namaqua rock mouse (Aethomys namaquensis, Muridae) getting dusted with pollen of the Pagoda Lily
(Whiteheadia bifolia, Scilloideae) while lapping nectar at the flowers = pollination
Biotic interactions:
Community Ecology
• A community is a group of populations of different species living in the same area at the same time, that may all
potentially interact
Competition
• Interspecific competition (–/–) occurs when organisms (from different species) compete for a shared limited resource,
with negative consequences for both
• Strong competition can lead to competitive exclusion (i.e., local elimination of a competing species)
= Gause’s competitive exclusion principle:
• two species competing for the same limiting resources cannot coexist in the same place
• an invasive species is an introduced organism that becomes overpopulated and negatively alters its new
environment
Competitive exclusion
An experiment with two species of floating duckweed, which are tiny angiosperms found in ponds and lakes. One species
grows more rapidly in pure culture than the other species. But another has tiny air-filled sacs that enable it to float on the
surface, and when the two species are grown together (3) shades (1) and is the victor in the competition for light.
Predation and herbivory
• Predation (+/–) refers to interaction where one species, the predator, kills and eats the other, the prey
• Herbivory (+/–) refers to an interaction in which an herbivore eats parts of a plant or alga – does not always result in
death
Symbioses
Symbiosis is a relationship where two or more species live in direct and intimate contact
• In parasitism (+/–), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in
the process. Pathogens and parasitoids (+/–) can cause the death of their hosts, while reproducing in their host
• Commensalism (+/0) is where one species benefits, and the other is unaffected (e.g., transport, nesting sites)
• Mutualism (+/+), is an interspecific interaction that benefits both species (e.g., pollination, mycorrhiza, parasite removal,
ants, and acacias)
Facilitation
• Facilitation (+ / +) or (0 / +) occurs when the presence of a species increases the survival and/or reproduction of other
species by changing environmental conditions
Interactions can vary
• Interspecific interactions are not constant
