Vocabulary:

• Population: a group of individuals of the same species, that inhabit a given area
• Population dynamics: patterns of continuous change over time
  • Takes into account birth, death, and migration
• Genet: a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor.
• Ramet: an individual that does not contribute to the sexual diversity of a population.
• Metapopulation: local subpopulations, connected by movement of individuals
• Age structure: graphs showing the distribution of males and females of specific age ranges within a population
• Epidemiology: dispersal of pathogens
  • Active vs. passive
• Density Dependent Growth: the number of organisms in the population directly affects the growth rate
  • Example: Resource allocation
• Density Independent Growth: the number of organisms in the population does not have an effect on the growth rate
  • Example: Natural disasters
• Minimum Viable Population (MVP): “smallest isolated population having a 99% chance of remaining extant for 1000 years despite the foreseeable effects of demographic and environmental stochasticity, and natural disasters”  
• Minimum Dynamic Area (MDA): area of suitable habitat necessary for maintaining the minimum viable population

Outline of Notes:

Population Structure:

• Population: a group of individuals of the same species, that inhabit a given area

• Population structure includes features such as:
  • Density
  • Age
  • Distribution

• Age Distribution/structure: the distribution of age groups across males and females in a given population, represented by age structure graphs:

Population Dynamics:

• Population Dynamics: patterns of continuous change in a population over time
  • Takes into account:
    • Births
    • Deaths
    • Movement (immigration and emigration of individuals)
      • Movement between populations is imperative to maintain a healthy gene pool and allow for population growth
• Population growth can be density-dependent or density-independent:
  • Density Dependent Growth: the number of organisms in the population directly affects the growth rate
    • Example: Resource allocation

• • Density Independent Growth: the number of organisms in the population does not have an effect on the growth rate
    • Example: Natural disasters

Biorender

• Sexual genet gives rise to asexual ramets:

• Genets are groups of genetically identical individuals such as plants, fungi, or bacteria, that have grown in a given location that have all originated vegetatively (not sexually) from a single ancestor.
• Ramets are individuals
  • Do not contribute to the sexual diversity of a population

Biorender?

Population Distribution:

• Geographic range vs. population distribution:
  • Geographic range: the area a population inhabits
    • Niche requirements at different spatial scales
    • Examples: worldwide, continental, region, physiographic area, cluster, locality, colony, or clump
  • Population distribution: how individuals in a population are distributed in a given area
    • Takes into account habitat suitability and geographic barriers
    • Population density is crude
    • Examples: random, uniform, clumped
• 3 different patterns of population distribution:

1. Random: no relationship (neutral interactions between individuals and the environment)

• • Most common when movement is dictated by other factors
    • Ex: wind dispersed seeds

2. Uniform: negative interaction (antagonistic relationship between individuals or local depletion of resources)

• • • Ex: Canopy trees competing for light in a forest

3. Clumped: occur in groups (attraction between individuals and/or to a common resource)

• • • Ex: Fish schooling to deter predation

Population Density:

• Crude density: includes all of the land within an organism’s range
  • Can be improved by maintaining habitats and ensuring connectivity between habitats/populations
  • Biorender
• Ecological density: includes only the portion of land that can actually be colonized by the species
  • Ecological density = # individuals ÷ unit suitable habitat
  • Accounts for patchiness
• Estimating population abundance and density:
  • Can be done by visually identifying animals of interest, listening for their calls, or identifying skat or footprints or through mark and recapture:

Dispersal and Migration:

• Plants often produce seeds with traits that enable them to take advantage of a particular dispersal mechanism; these can include fruits to attract animals or structures that allow them to be picked up by wind or attach to animals.

• Modes of dispersal for seeds:
  • Wind: random distribution
    • Ex: Milkweed (A) 

• Animal feces: clumped distribution
  • Ex: Mulberries (B) 

• Water: random and/or clumped distribution
  • Ex: Coconuts (C)

• Locomotive dispersal (attach to animal fur): clumped and/or random distribution
  • Ex: Burdock (D)

• Dispersal vs. Migration:
  • Dispersal: one way movement of individuals from their place of birth to a new environment
  • Migration: movement of individuals between habitats; can occur seasonally or daily and can occur over the course of multiple generations.

• Epidemiology: dispersal of pathogens
  • Active vs. passive
    

Exponential Growth:

• Exponential growth can be expected when:
  • A major disturbance event has occurred
  • A species is introduced to a new region
• Example: Invasive plants experience exponential growth when first introduced into a new environment that meets their needs.
  • Introduction phase (EDRR)
  • Colonization phase (Control)
  • Naturalization phase (Restoration)

The Human Effect:

• Humans have a variety of effects, both beneficial and detrimental, to the populations of plants and animals. These effects can include:
  • Decreased survivorship
    • Organisms with long life histories may not live long enough to reproduce
  • Increase survivorship
    • Organisms with short life histories may experience overcrowding due to rapid population growth
  • Decreased available habitat
    • Species may be restricted to a smaller than necessary range, decreasing their available resources.
      

      

• • • Ex: Smaller ranges can negatively affect the social behaviors of animals that hold territories, such as large carnivores.
• How does territoriality affect population growth?
  • Territorial species hold territories to control access to limited resources such as food, breeding grounds, and lookouts.
    • Territoriality can increase population stability by maintaining a uniform distribution pattern
• Conservation Implications:
  • Minimum Viable Population (MVP): the smallest isolated population that has a 99% chance of staying extant in the next 1000 years, despite the effects of demographic and environmental stochasticity and natural disasters.
  • Minimum Dynamic Area (MDA): the area of suitable habitat necessary for maintaining the minimum viable population

 Blog Style Summary:

When you hear the word population what is the first thing that comes to mind? The number of people in your city? Or even just a group of people? In ecology, the word population is related to those meanings, but has a more concrete definition. A population is defined as a group of individuals of the same species that all inhabit a given area. Furthermore, all the individuals in a population have the biological potential to interbreed and produce offspring, as well as inhabiting the same area, which can vary in scale from a microhabitat to the entire globe. For example, humans can generally all interbreed with each other so they have the potential to be viewed as a population. The given area changes the population at a fundamental level. For instance, the population of humans across the globe is definitely different from the population of humans in the Democratic Republic of Congo, and similarly is different from the population of humans in your local CVS pharmacy. All three of those populations are similar in that they include humans, but what defines those populations – density, age, and distribution of humans – are very different across the three. An ecologist would call these factors that define a population the population structure.

        A population structure is made up of characteristics that help better define a population. These characteristics are: the number of individuals in the population, the population density, or how many individuals inhabit a unit area, the population distribution, or how the individuals are arranged in the given area, and the age or sex of each individual. Each of these factors are helpful in learning more about a population. Population density is sometimes a fairly crude way of telling the density of a population because the population might be dispersed unevenly – for example, there could be a lot of land that is unusable to the population. We can adjust this crude density by calculating an ecological density that only takes into account the usable land for the population. This helps to account for the patchiness that we could sometimes see from a standard population density. This ecological density would take into account the variability of the actual habitat of the population. We can estimate population abundance, or the number of individuals in an area, with a mark and recapture technique. Scientists can mark individuals in an area, and then release them and recapture more of the population at a later time. The total number of individuals in that population can be estimated by multiplying the number of individuals marked with the number of individuals that were marked and recaptured. This number is then divided by the number recaptured to give an estimate of the population abundance.

        
Population dynamics are the patterns of continuous change, which can be separated into 4 categories: Births, Deaths, Emigration, and Immigration. Birth introduces new members to the population, which is essential for the population’s survival while death takes away members from a population whether it be old age or getting eaten by a predator. Emigration is when individuals of a population leave a given area for another area, which decreases the initial population while immigration is the opposite, where individuals join the population from another area. Movement, such as emigration and immigration, between populations plays a large role in population growth because it allows populations to maintain a healthy gene pool. Each of these 4 factors is important in determining the number of individuals within a population. We can compare and contrast the four population dynamics. For example, dispersal within a population is one way and only occurs once in an individual’s lifetime, whereas migration occurs in semi-regular intervals, and is usually a round trip. 

Another factor to consider is how the population reproduces. If a population reproduces asexually it could be called a genet. A genet is a group of genetically identical individuals, and the individuals that make up the genet would be known as ramets. While ramets can be considered individuals, they do not contribute to the sexual diversity of a population because they all have the same genetic makeup. This makes these populations very susceptible to changes in the environment, as there is no genetic variation that would allow for adaptation. Geographic range and population distribution can often be confused with one another, but they have distinct differences. Geographic range is where the population inhabits, whether that be the tropical island of Hawaii or the freezing cold Antarctic. The geographic range can often tell you some information about the life history traits of a specific species, such as how adaptive they are to different environments. Population distribution however is how the specific members are distributed within a given area. There are 3 types of distribution:
random, uniformed, and clumped.

Random distribution is when there is no relationship between individuals and the environment. Random distribution is most common when movement is dictated by other factors, such as wind-carrying plant seeds. Uniform distribution is when there is a negative relationship between individuals. This can be due to a lack of resources or competition that is causing individuals to stay away from one another. An example of this could be tree canopies; individual trees have a uniform distribution to maximize the amount of sunlight they receive. Clumped distribution is when there is an attraction between individuals and/or a common resource. An example of this could be a common water source or the need to stay in a group, such as a school of fish.

Overall when looking at population dynamics we must consider the additional factors that play a role in population survival. Human effects include an increase or decrease in a population’s survivorship. A decrease in survivorship is common in species with long life histories, as they are not able to live long enough to reproduce. On the other hand, species with short life histories may experience overcrowding. Additional factors, such as decreased habitats, play a major role in species’ life histories.

Spotlight on NC:

When considering any ecosystem, it is important to examine the populations of organisms that make up the system. Populations
are groups of organisms of the same species that live within a certain location. The way that individuals in a population are distributed can usually be described in one of three ways: randomly, uniformly, or clumped. Random distributions are where there is no pattern in the way that a species is found in an area. Populations that have a uniform distribution have individuals found in equal proportions throughout a given range. Finally, there are clumped distributions, where individuals of a species tend to be clustered in areas that have the resources that meet their needs. This last type of distribution is the most common, as resources typically are not found in the same quantities and proportions throughout a geographic region. Because of this, some populations can sometimes be divided into metapopulations that connect with each other via dispersal routes [1].  

There are innumerable cases of different types of population distributions across the state of North Carolina, and the wild horses are a prime example. Wild horses have lived on North Carolina’s barrier islands for around five hundred years, descending from Spanish mustangs brought by early explorers. They once occupied most of the island chain, but starting in the early 1900s the National Park Service took over a majority of the islands and moved most of the horses onto more remote, isolated islands [2]. Today, the NPS protects the horses, but there are only four populations of wild horses left on the islands, each with a clustered population distribution [2]. They roam together in herds, one cluster in each area. Herds can be found on the Rachel Carson Nature Preserve, Ocracoke Island, Shackleford Banks, and the Currituck Banks (see figure 2) [2]. However, these herds don’t make up a metapopulation, as a metapopulation is multiple subpopulations
 that interact with each other. The four remaining herds never come into contact with each other because they’re separated by the ocean.  

        Another wildlife species that has interesting population dynamics is the Virginia big-eared bat (Corynorhinus townsendii virginianus), a subspecies of the Townsend’s big-eared bat. This bat has a small geographic range in western North Carolina; it is only found near Grandfather Mountain and Beech Mountain [3]. Much of the population mates and hibernates in a cave on Grandfather Mountain every winter, and in late spring females move to a nursery colony on Beech Mountain to give birth to just one pup [3]. Virginia big-eared bats stay clustered together in a clumped distribution because of a lack of suitable habitat in North Carolina and also to ensure warmth and security while hibernating [3].

        These bats are highly sensitive to human disturbance. A decrease in available habitat from deforestation and development has negatively impacted the survival of the species, most likely because they are carnivores and endemic to specific western regions in North Carolina [3]. Virginia big-eared bats roost in places with wide, open ceilings, rather than in crevices or cavities [3]. Roosting sites are highly vulnerable to light and sound since bats are nocturnal [4]. This species is not migratory; however, when roosting sites are disturbed, the bat colony may have to leave and change roosting sites, risking their health and survival as a result [4].

Featured Ecologists:

Rashidah H. Farid, PhD

Dr. Rashidah Farid is a professor at Tuskegee University where she also runs her own Ecosystem Sustainability and Ecological Resistance Lab. In the ESER lab, Dr. Farid and her students focus on southeastern conservation and sustainable agriculture. Dr. Farid is a well-rounded ecologist with many areas of study including water pollution, population ecology, the accumulation of heavy metals in soils and trees, and the life history of Gunnison’s Prairie dogs (Figure 1.) In her research, she wanted to find out how age, sex, and reproductive status affect the survival rate of the Gunnison’s Prairie dogs (Cynomys gunnisoni). In this study, the capture-mark-recapture technique was used to estimate populations. It was found that female prairie dogs had higher survival than males. Prairie dogs less than one year had the lowest survival whereas juveniles and adults both had fairly high survival. Unlike many other species of prairie dogs, Gunnison’s Prairie dogs can reproduce as yearlings (one year old). Their survival for yearlings was significantly lower than in other species of prairie dogs. This may be evidence to suggest that reproducing so young may be costly. Research like that of Dr. Rashidah Farid on Gunnison’s Prairie dogs is important because it can help us understand long-term population trends in different organisms.

Robin Wall Kimmerer, Phd

Dr. Kimmerer is one of the few well-known bryologists in the country and asks groundbreaking questions about mosses. She explores competition, symbiotic relationships, dispersal limitation, and reproductive variability in sex.  She invokes concepts such as population density, competition mode, isolation on boulders, and the role of disturbance on a population. Her research is mostly based in the Adirondack Mountains in New York.

Dr. Kimmerer explores the integration of traditional and scientific knowledge to strengthen land management practices and restore ecosystems. She has been writing about this integration since 1998, with calls to action and several examples in published articles. In addition to journal articles, Dr. Kimmerer publishes essays and books combining these concepts, which is a delightfully approachable way for general citizens to learn about science topics. This may be the impactful and important work of Dr. Kimmerer, as she is paving the way for traditional knowledge in the academic scientific community.

She also works on the ecological restoration of culturally and ecologically significant plants such as sweetgrass and goldthread, as these plants have an evolved relationship with humans. Her research on revegetation is focused on abandoned mining areas, with bryophytes sometimes playing a role in revegetation.

Gloria Tom

Gloria Tom dedicates her life to wildlife conservation and has served on many projects regarding environmental issues. As a wildlife biologist and environmentalist, she has developed multiple wildlife management programs which encompass big game management and native recreational fish management. Together with the Arizona Game and Fish Department, she has collaborated on law enforcement policies and endangered species management. She also provided significant support to the Arizona condor program that strives to rehabilitate condors and downlist them from their ‘endangered’ status. In 2019, she appeared before the Subcommittee on Water, Oceans, and Wildlife to spread awareness about tribal wildlife conservation efforts and the challenges tribes have faced concerning their involvement in conservation. She also emphasized her support for the Recovering America’s Wildlife Act and the Wildlife Corridors Conservation Act. Within her 36-year career with the Navajo Nation, she also worked with the National Indian Youth Leadership Program which encourages youth to become capable, caring, and resilient individuals through outdoor leadership training and nature-centric activities. Gloria Tom’s desire to bring others into nature also takes form in her diligence to promote responsible and ethical behavior. In particular, she continues to deliver hunter education and collaborate on environmental issues for the residents of the Navajo tribe. Her leadership promotes the unity of traditional knowledge within the scientific community.

Student contributors:

Note Outline: Raven Yurtal, Anna Nelson, Alison Plumley, Mayla Ngo, Kolby Altabet

Blog Style Summary: Ben Meyer, Andrea Padilla, Nick Reenan, CJ Dierking

Spotlight on NC: Kyla Marze, Trey Jeffers, Nick Terwilliger

Featured Ecologists: Vanessa Schaefer, Em Trentham, Rebecca Olson