Ecology Lec | Population Distribution and Abundance

What is a population?

A group of individuals of a single species inhabiting a specific area

What are the characteristics of a population

Number of individuals, density | Additionally could be age distributions, growth rates, distribution and abundance

What are Distribution Limits?

Physical environment limits geographic distribution of a species

Why do distribution limits exist in organisms?

1. Organisms can compensate only so much for their environmental variation

   1. Organisms have their own specific tolerances

      1. extremophiles

      2. stenohaline

What is a niche, and what does it explain?

1. Niche is the set of all possible conditions in an environment which would allow a population to sustain itself

   1. Summarizes environmental factors that influence growth, survival, and reproduction of a species. Set of factors that allows a population to sustain itself.

What are the 2 types of niches

1. Fundamental Niche

2. Realized / Actual Niche

What is a fundamental niche and its characteristics

1. Broad, → set of conditions a species can occupy in an ideal condition → e.g. no competition and no predators

What is a actual / realized niche and its characteristics

1. Narrow subset of the fundamental niche, that may overlap with other niches of other species → which makes competition 

What is niche divergence?

1. Evolutionary process where closely related species or populations adapt to distinct ecological roles or environments, reducing competition for resource

2. Usually the environment favors this → if too much competition, eventually the get taken out 

What is the competitive exclusion principle?

1. No 2 species can occupy the  same niche at the same time indefinitely → only 1 species can hold a niche indefinitely 

What does the competitive exclusion principle illustrate in organisms?

Shows how abundance leads to diversification → which could lead to speciation

What is an example of the competitive exclusion principle in land mammals?

Kangaroo Distributions and Climate

1. Kangaroo species in Australia would compete for the same resources → now they moved around and now occupy their own niches

Are limited distributions always directly influenced by climate, explain why

No.

1. Climate often influences species distributions via 

   1. Food Production

   2. Water Supply

   3. Habitat

   4. Incidence of parasites, pathogens, and competitors 

Climate may not necessarily affect the species itself, but it can affect the stuff that the species is reliant on like its resources. 

What generalization does the experiment on Tiger Beetle of Cold Climates explain?

1. Supports generalization that the physical environment determines survivability which in turn limits species distribution 

How are plants distributed based on a moisture gradient

Encelia species distributions correspond to variations in temperature and precipitation 

What would organisms which live in intertidal zones be evolved to do, and what is an example of this?

1. Organisms living in an intertidal zone have evolved to different degrees of resistance to drying

   1. Barnacles show distinctive patterns of zonation within intertidal zone

Explain an example of zonation within an intertidal zone from Barnacles

1. Connell found Chthamalus stellatus restricted to upper levels while Balanus balanoides is limited to middle and lower levels 

   1. note : as larvae, barnacles typically have more choices

Summarize the barnacle experiment by Connell

1. C. Stallatus : small, and are better in dry environments

   1. Biotic : competition in B. Bela 

2. B. balanoides : big, and are bad in dry environments

   1. Abiotic : dryness of the environment 

3. Note : C Stellatus does not compete with B. Balanoides because of competition, and the likelihood of being outcompeted by B.

How do Balanus, and Chthamalus exclude each other?

Balanus appears to be more vulnerable to desiccation (extreme drying), hence they are excluded from the upper intertidal zone.

1. Chthamalus adults appear to be excluded from lower areas by competition with Balanus 

What are the 3 types of distribution of individuals on the small scale?

1. Random

2. Regular

3. Clumped

What is random distribution and its processes?

1. Equal chance of being anywhere (equal chance of being found in any spot)

2. Uniform distribution of resources (if u can find resources anywhere, u can find organisms anywhere)

3. Neutral interactions between individuals and between individuals and local environment

What is regular distribution and its processes?

1.  Uniformly spaced (evenly spaced apart)

2. Individuals avoid each other (biotic)

   1. Competition spaces these organisms away from each other

3. May do allelopathy

4. Antagonistic interactions between individuals or local depletion of resources

What is allelopathy

1. Mechanisms where plants leech toxic chemicals into the soil to outcompete other plants 

What is clumped distribution and its processes?

1. Unequal chance of being anywhere 

2. Individuals live in areas of high local abundance which are separated by areas of low abundance 

3. Mutual attraction between individuals (biotic)

4. Patchy resource distribution 

5. Process

   1. Attraction between individuals or attraction of individuals to  a common resource 

What is the Distribution of Tropical Bee Colonies?

1. Hubbell and Johnson predicted aggressive bee colonies would show regular distribution while non-aggressive species would show random or clumped distributions

2. As predicted, 4 species with regular distributions were highly aggressive

   1. 5th was non-aggressive and randomly distributed 

   2. Prospective nest sites marked with pheromones (type of competition) 

What is the Distribution of Dessert Shrubs 

1. Traditional theory suggests desert shrubs are regularly spaced due to competition

2. Phillips and MacMahon found distribution of desert shrubs changes from clumped to regular patterns as they grow

Why would dessert shrubs typically grow in clumped systems?

1. Seeds germinate at safe spaces (when enough water is found)

2. Seeds not dispersed far from parent areas

3. Asexual Reproduction 

As plants like dessert shrubs grow what did Phillips and MacMahon find? Additionally what was the findings of Brisson and Reynolds in dessert shrubs.

1. Competition among remaining plants produces higher mortality

   1. Eventually it creates regular distributions 

2. Brisson and Reynolds found competitive interactions with neighboring shrubs appear to influence distribution of creosote roots, Larrea tridentitata.

How do Distributions of individuals on large scales work?

1. Bird populations across North America 

   1. Root found at continental scale, bird populations showed clumped distributions in Christmas Bird Counts. 

2. Clumped patterns occur in species with widespread distributions

3. Brown found a relatively small proportion of study sites yielded most records for each bird species in the Breeding Bird Survey. 

How are Plants Distributed along Moisture Gradients 

1. Whittaker examined distributions of woody plants along moisture gradients in several North American mountain ranges

   1. Documented moisture gradient from moist canyon bottoms up to the dry south-west facing slopes

In moisture gradients what kind of distribution do trees typically show, and why is this?

1. Tree species showed a highly clumped distribution along moisture gradients, with densities decreasing substantially towards the edges of their distribution 

2. Note : trees survive when their environment is ,most suitable to them

What is dispersal?

1. Movement of an individual from one environment to another → could be the movement of in and out of a population 

2. Movement of individuals either through range expansion (over continuous favorable habitat) or jump dispersal (past a barrier)

What are the major factors which dictate and influence dispersion

1. Island species are characterized by high dispersal abilities

2. Endemicity (explained by lack of dispersal) is high in areas not characterized by opportunities for dispersal

3. Most island species are clearly related to species on the earnest mainland 

   1. Bc most of the species come from a common ancestor

Why are island species characterized by high dispersal abilites?

Since its harder to get o islands compared to land —> meaning for you to have arrived in an island you may have needed greater dispersion such as wings for birds

Why is Endemicity high in areas where no dispersal occurs?

Organisms dont typically move far, which means that they can’t get farther away from where the disease is for example.

Where did Galapagos Finches from the mainland likely originate from?

The Caribbean

What is Biogeography, and what are the factors which affect Biogeography

1. Biogeography : movement of a population

2. Factors that affect Biogeography

   1. Dispersion

   2. Extinction 

What is immigration and emigration

1. Immigration : movement of individuals into a population

2. Emigration : movement of individuals out of a population 

What are metapopulations?

1. type of population structure responsible for the stability of a population 

2. A metapopulation is made up of a  group of subpopulations living on patches of habitat connected by an exchange of individuals 

3. Examples

   1. Alpine Butterfly

   2. Lesser Kestrels

What are Alpine Butterflies a victim of

habitat fragmentation

Why does habitat fragmentation lead to Metapopulations?

Its due to the patchiness of the habitat → hence there are areas wherein the subpopulation resides

Is a subgroup a metapopulation?

1. each subgroup is NOT a metapopulation, every subgroup is a metapopulation 

What is the term for a one species / local extinction?

Extirpation

What are the characteristics of the Classic Metapopulation Model

1. Habitat occurs in discrete patches

2. All populations have a substantial risk of extinction

3. Dispersal occur among all patches 

4. Patch dynamics are asynchronous

5. Ignore population dynamics within a patch 

Why do populations in the classic metapopulation model have a risk of extinction

1. if patches stop exchanging → leads to local extinction due to resource scarcity 

What does asynch patch dynamics mean?

1. what happens in one patch is not the same in the other patches 

What is the source sink model?

1. Source only moves from one place to another

   1. Better to protect the source → bc this is where everything comes from hence is better to protect it 

What happens to population density when organism size increases, and why?

1. In general, population density declines with increasing organism size → bc density is about how many organisms fit in one area 

What did Damuth find about the population density of herbivorous mammals

Damuth found the population density of herbivorous mammals decreased with increased body size

What did Peters and Wassenberg find about aquatic invertebrates’s population density

1. Peters and Wassenberg found aquatic invertebrates tend to have higher population densities than terrestrial invertebrates of similar size

Do mammals and birds of the same size have similar population densities?

No, likely due to

1. Due to birds have narrow niches

2. Birds tend to live only in upper canopies of the trees vs mammals with free range 

What happens to plant population density overtime with increasing plant size

1. Plant population density decreases overtime with increasing plant size 

   1. Underlying details are very different 

      1. Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities. 

What are the 3 factors which influence the classification of rarity?

1. Geographic range of species / geographic distribution

2. Habitat Tolerance 

3. Local Population Size 

What are the characteristics of populations less likely to face extinction likely have

1. Populations that are least threatened by extinction, have extensive geographic ranges, broad habitat tolerances and some large local populations

In terms of survivability, what would happen to organisms that are highly specialized?

the more specialized a species is, the rarer it is → the more specialized = the narrow survivability 

What are the 3 types of rarity

1. Rarity I

2. Rarity II

3. Rarity III

What are the characteristics of Rarity I

1. Rarity I ( big range, broad tolerance, and small local populations)

   1. Extensive Range, Broad Habitat Tolerance, Small Local Populations

What are the characteristics of Rarity II

1. Rarity II (big range, large population, narrow tolerance)

   1. Extensive range, large populations, narrow habitat tolerance 

      1. Passenger pigeon 

What are the characteristics of Rarity III

1. Rarity III (small range, narrow tolerance, small populations)

   1. Restricted range, narrow habitat tolerance, small populations 

      1. California Condor