Metapopulations

Question 1

Key terminology

Answer 1

• Metapopulation: a group of spatially distinct populations,
  distributed between discrete habitat patches connected by migration. They are often
  referred to as a population of populations
• Population: a group of individuals of the same species that interact with each other
  in the same place at the same time. This may be further divided into localised sub-
  populations
• Patch: A place where a population could exist. There are two main types source and
  sink (we will cover these later)
• Disperser: a term used to refer to an individual that migrates to another patch
  (University of Idaho, 2010)

Question 2

Why this is of interest to ecologists/ influence on conservation efforts

Answer 2

Land use change, characterised by urbanisation, agricultural expansion, and infrastructure development, has emerged as a significant driver of habitat fragmentation, profoundly impacting metapopulations and continues to be the main causative agent in driving species extinctions (Semper-Pascual et al., 2021)

As habitats both become more isolated and smaller in size, species encounter barriers that impede migration and limit access to suitable habitats, ultimately increasing the risk of local extinctions (Cheptou et al., 2017).

Human induced climate change exacerbates these effects, by altering the seasonality, temperature and precipitation ranges of areas, leading to altitudinal and latitudinal habitat shifts/ (Drechsler and Johst, 2017)

Question 3

Summary of 4 main models

Answer 3

Summary of models:

Levins (classical)
- Patches are prone to extinction
- However, patches are sufficiently connected for recolonization of unoccupied patches to occur and the metapopulation to persist
(Harrison,1991)

Non-equilibrium
- Small patches, highly isolated so no dispersal or recolonisation occurs.
- Each population is independently a metapopulation.
- So when a sub-population goes extinct, this results in the extinction of both the subpopulation and the entire metapopulation.
(Harrison,1991; Hanski, 1997)

Patchy
- Consists of both small and large patches
- Populations are highly connected by migration of dispersers
- Patches are united as a single population and metapopulation
- low probability of populations within patches going extinct
(Harrison 1991)

Mainland-Island
- A large ‘mainland’ patch interacting with smaller ‘island’ patches nearby.
- Dispersers from the mainland can reach all subpopulations, ensuring that as long as the mainland population persists, the metapopulation does not go extinct.
(Harrison 1991)

(see notes for diagram)

Question 4

Comparison of models by patch size/ isolation

Answer 4

Comparison of models by patch size/ isolation

Classical (or Levin’s - Connected small patches

Patchy - Highly connected small and large patches

Non-equilibrium - Highly isolated small patches

Mainland-Island - A large patch (sometimes more than one) connected to surrounding small patches
(Aycrigg et al., 2014; O’Neill, 2020; University of Idaho, 2010)

Question 5

Some models have vacant patches:

Answer 5

Some models have vacant patches:

Classical – vacant patches have the potential to be colonised

Patchy - No vacant patches

Non-equilibrium - When vacant patches occur they are rarely recolonised (due to low dispersal)

Mainland-Island - Vacant patches have the potential to become colonised
(Aycrigg et al., 2014; O’Neill, 2020; University of Idaho, 2010)

Question 6

A patch is a place where a population could exist.
There are two main types of patch:

Answer 6

A patch is a place where a population could exist.
There are two main types of patch:

• Source: migration is high from this patch TO other patches
  (generally a large population)
• Sink: population is in decline, this type of patch receives immigration but has little emigration
  (generally a small population)

Rate and direction of dispersal allows us to determine source and sink patches. This is most
clearly observable in the Mainland-Island model
Which has one source patch and many sink patches.
However in other models sources may become sinks and vice versa
(O’Neill, 2020; University of Idaho, 2010)

Question 7

Each metapopulation model has different population boundaries:

Answer 7

Each metapopulation model has different population boundaries:

Classical (or Levin’s) - Each patch a population

Patchy - All patches form one population due to being highly connected

Non-equilibrium - Each patch a population

Mainland-Island - Patches may be connected due to proximity to mainland
(Aycrigg et al., 2014; O’Neill, 2020; University of Idaho, 2010)

Question 8

Metapopulation models compared by dispersal rate and direction:

Answer 8

Metapopulation models compared by dispersal rate and direction:

Classical (or Levin’s) - Migration occurs between patches, some unoccupied patches are also present.

Patchy - Frequent migration resulting in flux between patches

Non-equilibrium - Almost no migration due to high isolation. Migration does occur – but at very low rates

Mainland-Island - Unidirectional dispersal from the mainland
(Aycrigg et al., 2014; O’Neill, 2020; University of Idaho, 2010)

Question 9

Metapopulation models compared by boundaries of metapopulations:

Answer 9

Metapopulation models compared by boundaries of metapopulations:

Classical (or Levin’s), Patchy and Mainland-island all patches make up one metapopulation

In Non-equilibrium – each patch is a metapopulation due to low levels of interaction between patches

Question 10

Levins model example: Black-Tailed Prairie Dog - background info

Answer 10

Metapopulations of the Black-Tailed Prairie Dog (Cynomys ludovicianus)
Prairie dogs are a key-stone species.
They positively influence their ecosystem in 3 main ways:
-burrowing
-grazing
- providing food for other animals
This positively influences:
- biodiversity
- nutrient cycling
- environmental heterogeneity
- hydrology
- landscape- level processes
(Burnaugh,2018; Mulhern & Knowles, 1997; Prairie Dog Coalition, no date)
(Young, 2018)

It is estimated that the population now occupies ~2% of its historic range

Question 11

Causes of Black Tailed Prairie Dog Range Contraction

Answer 11

Causes of Black Tailed Prairie Dog Range Contraction

Disease: - Sylvatic plague -Tularia

Culling: - intensive control programs -unregulated recreational shooting

Land use change: - conversion of habitat to agriculture - urbanisation

Climate change: - increase in droughts

Question 12

A study of the North Colorado Metapopulation (13 patches aka colonies) found that Black tailed Prairie dogs showed the 3 key traits of (Levins) model:

Answer 12

• Acting as one metapopulation
• Patches prone to extinction and recolonisation
• Patches are independent
  These traits were confirmed by genetic analysis.
  (Roach et al. 2001) (Roach et al. 2001)
  (Young, 2018)

Question 13

Limitations of the Levins Model

Answer 13

Limitations of the Levins Model

Patches are assumed identical -All vary in resource abundance, population growth rate etc.

Degree of isolation, immigration rate and habitat patch size are assumed constant
^These factors can be impacted by human interference, natural disaster or disease with temporary or permanent impact
(Etienne 2002)

Question 14

Patchy model example: Glanville Fritillary Butterfly metapopulation
Habitat patches have been created by:

Answer 14

• Naturally heterogenous landscape
• Land use changes
• Availability of larval host plants, and nectar

Question 15

4 key traits show the butterfly metapopulation is patchy:

Answer 15

4 key traits show the butterfly metapopulation is patchy:

Patches are well connected and often closely situated

Sub-populations can be extinction prone: 74% of sub-populations are below
the extinction threshold. Adults migrate a maximum of 3km in a lifetime, <1% of the total reserve area … but the metapopulation is rarely at risk of going extinct

Sub-populations are closely linked by migration dynamics: Can support 4248 patches and up to
30,000 adults. If a patch goes extinct, it does not significantly affect dynamics at the metapopulation level

The metapopulation is stable over time: e.g. Aland Island metapop has been stable for 17 years

^(Hanski et al 1995 and Ojanen et al 2013)

Question 16

Non-equilibrium model example: Desert Bighorn Sheep

Answer 16

• Small patches, highly isolated
• Very low dispersal rates (0.1-1%) so no recolonisation occurs
• Each population is independently a metapopulation
• Sub-population extinction means extinction of both the subpopulation and the entire metapopulation
  (Harrison,1991; Hanski, 1997)

Question 17

Desert Bighorn Sheep facts

Answer 17

Desert Bighorn facts:

Location: South West USA and northern Mexico
Habitat: Steep, rocky terrains and cliffs
Diet: Grasses such as catlaw acacia

Federally endangered species, at the beginning of the 19th century population was ~ 2,000,000
Today’s population is just 70,000
(Arizona Sustainability Alliance)
(Nevada Department of Wildlife)
(southwestdesertflora.com) (Creech et al., 2014)

Question 18

Causes and results of Desert Bighorn Range Fragmentation

Answer 18

Causes: Human developments such as highways, solar and wind farms and the US/Mexico border and climate change

Outcomes: Low level connectivity between metapopulations resulting in lower survival rate after infectious diseases (small gene pool due to small metapops = lack of tolerance variation), reduced diet quality and potential extinction. Climate change reduces food quality and rainfall as well as causing increased temperature.

Question 19

Possible solutions for Bighorn sheep and other non-equilibrium metapopulations

Answer 19

Additional protection: of occupied habitat patches + creation of dispersal corridors

Reintroduction or relocation

Removing existing barriers

Question 20

Mainland Island model metapopulation example: Fire Salamanders

Answer 20

Key features

Sub-populations act as one metapopulation

Sub-populations are not extinction prone

Sub-populations are not independent

see diagram in notes for island biogeography

Question 21

Methods of study

Answer 21

Mark-recapture and mark- release-recapture studies

Population size, survival rates, movement patterns and distribution within metapopulations
o N = (n1 + n2)/n3
o N = population size
o n1 = total caught in all samples (minus the first attempt)
o n2 = total marked (caught in first attempt)
o n3 = total recaptured

Habitat surveys - Key factors that influence distribution and persistence of metapopulations

Population monitoring - Information on population trends, potential threats, and management needs within metapopulations

Longitudinal ecological studies - Long-term trends and resilience of metapopulations

Radio telemetry - Spatial ecology, dispersal patterns and habitat use of individuals

Geographic information systems (GIS) - Maps habitat fragmentation, connectivity and land use changes

Genetic analysis - Potential for inbreeding or loss of genetic diversity for metapopulation viabilit

Population viability analysis (PVA) - Evaluating conservation status

Minimum viable populations (MVP’s)

Minimum population size required for a subpopulation to persist in a habitat patch

MVPID formula:
o Ne = (4NcNr)/(Nc +Nr)
o Ne = effective population size
o Nc = number of breeding individuals contributing to the next generation
o Nr = breeding sex ratio (number of contributing females / number of contributing males)
Mathboy321 (2023) Minimum viable population, Wikipedia:
https://en.wikipedia.org/wiki/Minimum_viable_population

Question 22

How can we conserve metapopulations

Answer 22

Example: Northern Spotted Owl (Strix occidentalis caurina)
Challenges:
* Highly fragmented habitat due to logging of ancient forests. 80% destroyed by 1980s.
* In 1995, ~8000 owls left - falling by 7% /year.
* One breeding pair occupies around 800ha and usually has only one fledgling a year.
Solutions:
* Spotted Owl Management Areas (SOMAs) were created. Same average size and distance apart.
* Further research showed the metapopulation could be kept viable with a network of areas of greater than 20 territories and less than 19.2 km apart. (McCullough et al., 1996)(McCullough et al., 1996)

Question 23

Problems we face: a new approach must be taken …

Answer 23

• Real world metapopulations exhibit a source/sink structure
• Habitat change is leaving patches unsuitable for colonisation or removing them entirely
• Habitat fragmentation makes traditional conservation methods unsuitable
• Processes occur over large scales of time and space
• Data can often be hard to collect and create applicable conservation strategies
  (McCullough et al., 1996); (Seiler, 2003)

Question 24

Conservation: Solution 1: Holistic landscape management

Answer 24

1. Human growth is inevitable, making infrastructure removal challenging. Management should prioritize optimal patches in the landscape.
2. Establishing border regions around reserves is crucial due to the sensitivity of many populations to external influences.
3. Implementing corridors for movement between patches or clustering them closely is essential in the design.
4. Regular monitoring and maintenance of the environment surrounding reserves are necessary

Question 25

Conservation: Solution 2: Reintroduction

Answer 25

Reintroduction is a conservation strategy that can aid in the preservation of metapopulations. By transferring individuals from a large source population to areas at risk, it can prevent extinction. Additionally, introducing individuals to uncolonized areas with suitable habitats can establish new metapopulations (Armstrong & Seddon, 2008).

(see diagram from Seiler, 2003)

Could allow us to:
- Ensure that individuals have access to the best possible patches.
- Allow colonisation of isolated patches.
- Re-open corridors between different patches, reestablishing gene flow.
(Armstrong & Seddon, 2007); (Seiler, 2003)

Raises questions about harvesting organisms from source populations, necessity of
translocation and quality of habitat.
(Armstrong & Seddon, 2007); (Seiler, 2003)

Question 26

The future of metapopulations?
Going forward with conservation methods we must consider that:

Answer 26

1. Metapopulation models should be used as a starting point for conservation strategy, as different metapopulations have different needs.
2. Reintroduction may be our best hope in keeping metapopulations viable due to human
   population growth.
3. Ecologists need to be able to demonstrate to policy makers and the general public the importance of metapopulations, not just environmentally but also economically.

(Nowosad et al., 2018)