Population Ecology Dynamics of Ecosystems
I. Ecological Hierarchy Individual Population Community Ecosystem Biome Biosphere
II. Population: same species living in an area } Species = group of similar organisms that can interbreed } Example: all the Giant pandas in a forest III. Community: group of different populations living in same area } Example: All the different plants & animals in a forest with the panda
} Definitions } Population Ecology: major sub-field of ecology that deals with dynamics of species populations & how these pops interact with the environment } Population Dynamics: studies short- and long-term changes in size, density & age distribution of pops, and the biological and environmental processes influencing those changes Birth and death rates Immigration and emigration Pop decline
Population Distribution aka Dispersion: Clumped helps w/ protection Uniform helps reduce intraspecific Random seen in some plants
Population Size o Changes with 4 variables: 1. Births 2. Deaths 3. Immigration 4. Emigration Pop change = (Birth + Immigration) (Death + Emigration) Age structure also influences pop change o = Numbers of prereproductive, reproductive, & postreproductive individuals
Biotic potential = Populations vary in their capacity for growth o Intrinsic rate of increase (r) = rate of pop growth w/ unlimited resources A pop with few resource limitations will grow exponentially (J-shaped curve): o *Humans
} Most pops grow < intrinsic rate of increase (r) b/ c of environmental resistance } Environmental resistance: all factors that act to limit pop growth } Can be Abiotic or Biotic } Can be Density-independent or Density-dependent https://www.youtube.com/watch?v=qi2ixjeixeu Serious Science Biological Carrying Capacity
} Density-independent factors = Any factor in the environment that does not depend on the number of members in a population per unit area Weather events Fire Human alterations of the landscape Air, land, and water pollution
} Density-Dependent Factors Any factor in the environment that depends on the number of members in a population per unit area Predation Disease Competition Parasites
Biotic Potential vs. Environmental Resistance o Generally come to some equilibrium:
Carrying Capacity (K) = max number of individuals of a given species that can be sustained indefinitely in a given space o = equilibrium b/w biotic potential and environmental resistance Populations w/ a carrying capacity show logistic growth (Sshaped curve): o Start off with rapid exponential growth o Followed by a steady decrease at K
Logistic Population Growth:
} Some organisms overshoot carrying capacity à results in a pop crash (dieback) } Due to reproductive time lag (period needed for birth rate to fall & death rate to rise in response to resource overconsumption) Tasmanian Sheep Alaskan Reindeer
There are 4 Types of Population Change Curves
} 4 Types of Population Change Curves 1. Stable: stay generally around K } Seen in consistent environments like tropical rain forests 2. Irruptive: stay stable except for occasional peaks & crashes } Seen in insects & algae (in temperate climates); raccoon & house mice 3. Cyclic: regular fluctuations } Seen in lemmings; lynx & hare 4. Irregular: no pattern
Predator & Prey Population Cycles o Pop cycles of predator influence pop cycles of prey & visa-versa o Examples: Lynx & Hare; Wolf & Moose** (**worksheet)
Sexual Strategies & Patterns: Asexual reproduction: does not require sex cells (gametes). Aka Mitosis cloning. o Bacteria reproduce this way. Only 3% of all species use this form Sexual reproduction: requires gametes à results in genetic recombination Disadvantages ½ pop doesn t give birth Increased chance of genetic defect/error Courtship and mating rituals can be complex Advantages Genetic variety/diversity!! Parents can divide responsibilities
Sexual Strategies & Patterns: o Reproductive Patterns: 2 types Classification of species reproductive pattern depends on their position on the population growth s-curve o r-selected species o K-selected species https://www.youtube.com/watch?v=bu6oukt9zhs Bozeman Science
r- selected species/ Opportunists o Capacity for high rate of pop increase o Reproduce early o Many, small offspring Most don t survive o No/ little parental care o Generalist niche o Examples: Algae Bacteria Rodents Insects Annual plants
K-selected species/ Competitor o Show lower pop growth rate o Reproduce late in life o Few, larger offspring o More parental care o Specialist niche o Do well in competitive situations, with stable env conditions o *Prone to extinction o Examples: Large mammals Birds of prey Large, long-lived plants
Different reproductive strategies have different types of survivorship: o = percent of individuals surviving to certain ages 3 Types of Survivorship Curves:
3 Survivorship Curves: Type I: Late Loss o Low infant mortality & long life spans o Tend to be K-selected species o Examples: humans (in developed countries); large mammals (elephants, big cats, etc.) Type II: Constant Loss o Death rate even among all ages o Examples: some birds, some invertebrates, rodents Type III: Early Loss o High infant mortality and then constant mortality for few remaining o Seen in most r-selected species o Examples: annual plants, small fish, marine invertebrates, insects
Community Ecology How do organisms interact?
Community Ecology Community Structure is based on: 1. Physical Appearance: size & distribution of its populations 2. Species Diversity: combination of o Species richness: # of different species o Species evenness: abundance of individuals within each species 3. Niche structure: # of niches and species interactions
Species Equilibrium Model (E.O. Wilson) aka Theory of Island Biogeography o Balance b/w 2 variables determines the number of different species found on an island : rate at which new species immigrate to the island rate at which existing species become extinct on the island 3 factors must be taken into account: 1. Immigration and extinction rates 2. Island size 3. Distance from mainland Useful when protecting wildlife on habitat Islands a.k.a areas surrounded by development
Remember the Major Roles that Species Can Play within Ecosystems cont.: 1. Native 2. Nonnative (Invasive) 3. Indicator 4. Keystone 5. Foundation species
SE Asia Durian Fruit & Bats (a.k.a Flying Foxes) Mutualism (+, +) Endangered due to 1. hunting for their meat 2. Deforestation 3. Targeted to keep them from eating commercially grown fruit Keystone 1. sustains tropical community 2. pollinates many plant species 3. disperses seeds in droppings & therefore maintains forest biodiversity https://www.youtube.com/watch?v=69igcip-azg
Invasive Species 1957 Brazil imported African Bees for honey production, instead they displaced domestic bees and reduced honey supply They have since moved north & reached the United States They are aggressive & unpredictable, kill 1000 s of domesticated livestock and about 1000 people due to allergies So far winter stops them from spreading farther north https://www.youtube.com/watch?v=y7c--cv4gpw
Indicator Species Species What do they Indicate? Trout Water Quality; require clean water w/high D.O. Birds & BuAerflies Chemicals & habitat loss; found everywhere Amphibians (frogs, salamanders, & toads Pollutants in air, water, & soil, UV light, habitat loss (filling in wetlands), drought, overharvesting; Live in water as herbivores & as adults on land as carnivores, thin permeable skin, eggs have no protection, https://www.youtube.com/watch?v=bvidpapf1bg Sci Show https://www.youtube.com/watch?v=1q5oe33m15q Scary Bat Die off http://www.smithsonianmag.com/videos/category/wildlife/saving-amphibians-from-deadlyfungus/ Amphibian Chytrid Fungus
Keystone & Foundation Species: American Alligator hunted for meat, skin, and/or for sport 1950-1960 90% decline in LA 1967 put on endangered species list 1977-1987 upgraded to threatened list in 8 states Keeps areas free of vegetation, digs deep depressions that fill with water & serve as refuge for aquatic life, feed on predatory gar https://www.youtube.com/watch?v=_iww8ruz8uo Keystone Species and their Role 3:59 https://www.youtube.com/watch?v=0-pe3ve3w2w Bozeman Science 7:35
Species Interactions: Competition= occurs between two species for resources (food, space, etc.) Gause s principle states that no 2 species can occupy same niche at same time à 1 species must relocate, die out or change niche Over a time scale long enough for natural selection, Resource Partitioning can occur:
Species minimize competition by filling specific niches within an ecosystem (traits allow them to utilize resources at different times, locations or ways) Ex: North American warblers hunt for insects in same spruce trees, but at different parts & times Symbiotic Relationships An interactive association between two or more species living together Predation (+, -) Interaction b/w organisms in which one organism (predator) captures and feeds upon another (prey)
Preys Defense Mechanisms: Physical adaptations: highly developed sight & smell; shells; spines; thorns; Camouflage & mimicry Chemicals: poisons, irritants, odors, ink clouds Behaviors: puffing up, mimicking a predator, playing dead Cuttlefish Hognose snake Praying mantis
Parasitism: when one organism (parasite) feeds on or otherwise harms another organism (host) in close association (+,-) Different from predation in that parasite is generally smaller than host and doesn t kill host, but harms over time Tick (Ectoparasites) Mistletoe Brood parasitism Video: https://www.youtube.com/watch?v=xukjbibbal8 David Attenborough Parasites
Commensalism: benefits one species but has little or no effect on other species (+, 0) Whales & Barnacles Epiphytes (Bromeliads & some Orchids)& Trees
Mutualism: interaction benefitting both species (+, +) Pollination Mutualism Nutritional Mutualism: Lichen (fungi & algae) Gut Inhabitant Mutualism
All communities change their structure & composition over time in response to each other & changing environmental conditions Disturbances: change in environmental conditions that disrupts a community or ecosystem. These disturbances can range from mild to catastrophic and can be caused by natural occurrences or human activities: Ecological Succession = gradual change in species composition Two Types: Primary Succession Secondary Succession
Primary Succession: the gradual establishment of biotic communities on lifeless ground (rock) Pioneer Species start soil formation process: trap soil particles & detritus in wind, secrete acids to break down rock Pioneer Species (Lichens, Algae, Bacteria, Moss) Mid successional species Late successional species End in Mature Community (long-lived hardwoods)
Secondary Succession: when biotic communities are established in an area where some type of biotic community is already present Occurs after disturbance (burned forest, polluted stream, abandoned farmland)
Intermediate Disturbance Hypothesis: communities that experience fairly frequent but moderate disturbances have the greatest species diversity
Succession Model Online http://www.mrphome.net/mrp/succession.swf
Measuring Biodiversity o Shannon s Diversity Index (H): range from 0 to 5 (more diverse) o Simpson Diversity Index (D): range from 0 (zero diversity) to 1 (infinite diversity)
Shannon s Diversity Index s H = - (P * ln P ) i i i=1 H = the Shannon Diversity index P i = fraction of the entire population made (n i /total) S = numbers of species encountered = sum from species 1 to species S up of species i
Simpson Diversity Index s D = 1 - [(n / N) 2 ] i i=1 D = the Simpson Diversity index n i = number of individual per species N = total number of individuals S = numbers of species encountered = sum from species 1 to species S
Shannon s Diversity Index Birds N i P i ln P i - (P i * ln P i ) Pigeon 96.96 -.041.039 Robin 1.01-4.61.046 Starling 1.01-4.61.046 Crow 1.01-4.61.046 House Sparrow 1.01-4.61.046 H = 0.223 High values of H would be representative of more diverse communities. If the species are evenly distributed then the H value would also be high. So the H value allows us to know not only the number of species but how the abundance of the species is distributed among all the species in the community.