BISC530: Biology Conservation Kedong Yin Introduction Habitat fragmentation Demographic Processes on heterogeneous landscapes: Metapopulation dynamics

Demographic Processes: Population Dynamics on Heterogeneous Landscape What is population demography? Mechanisms of population regulation Habitat-specific demography Population viability analysis The landscape approach

1. What is population demography? The study of population fluctuations due to birth, immigration, death, emigration (BIDE) population structure such as age structure, sex ratio and life history. BIDE + Population structure: age and sex ratio + life history (e.g. insects, fish) Birth Popul. Size Structure Immigration Emigration Death

6 1945 1985 1940 Years

Hong Kong Age Structure in 1998

Hong Kong Sex Ratio Age 35 Female Male

District 81 86 91 81-86 86-91 81-91 Tuen Mun Sha Tin

Seal Population changes on two islands occupied by US Coastal Guard: Juvenile survival is important in conserving seal populations Tern Island Coastal Guard in Coastal Guard out Green Island Number of Seals 1980 1960 1970

2. Mechanisms of population regulation: Environmental Factors Abiotic: Habitats Light Temperature Precipitation Nutrients Biotic: Intraspecific competition Interspecific competition Grazing/predation Parasitism/disease

Population regulation: density-regulation Mortality Density-dependent Density-independent Rate of Birth or Death Survival Density-dependent Population Density

Population regulation: Survival Strategy Type I-Mammals Survival Rate Type II - Birds Type III - Fish Age

Population Regulation: prey-predator relationships Abundance Time

Mechanisms Allowing Species Diversity: Resource Sharing and Niche Partitioning Species 1 2 3 Relative Growth Rate Resource State Temporal or/and Spatial Variation e.g. Habitats, Precipitation Light, Temperature, Nutrients

Mechanisms Allowing Species Diversity: Predator control Predators Relative Abundance Species 1 2 3 Resource State

Mechanisms of Population Regulation: A Hierarchy Approach Land use change Climate change Succession Disturbance Landscape Level Birth rates Death rates Immigration Emigration Sex ratio Age structure Population Level Growth rates Feeding rates Habitat selection Predator Avoidance Individual Level

3. Habitat-specific demography Sources and Sinks: Metapopulation Concepts

Equilibrium Theory of Island Biogeography: Species richness is the balance between colonization and extinction rates Colonization Extinction Near: N Small: S Rate of Colonization or Extinction Large: L Far: F S-FS S-FL S-NL S-NS Low High Species Richness #

The key conservation legacies of the dynamic theory of island biogeography were: 1) Arriving at two most robust empirical generalizations of biology and ecology (1) Extinction rates decline with population size (2) Immigration and recolonization rates decline with increasing isolation 2) Species-area relationship 3) The metaphor of a refuge as an island 4) The interest in the fragility of the biota of individual refuges and causes of this fragility 5) The rules of refuge design

Metapopulation Sources and Sinks Sources: good habitats where local reproductive success is greater than local mortality and individuals disperse outside their natural patch to find a place to settle and breed. As little as 10% of a metapopulation in source habitats may be responsible for maintaining the 90% of the population found in the sinks Sinks: poor habitats where local reproductive success is less than local mortality and the subpopulations rely on immigrations to avoid extinction

Implications of Sink and Source Concept for conservation: 1. Critical habitats should be defined by habitat-specific reproductive success and survivorship not population density -- important (Until recently, critical habitats were defined as the places where a species was most common). e.g. Peregrine Falcon: two subpopulations (northern California and southern California): northern subpopulation acts as a source for southern population. 2. Reserve design: identify sources and sinks Management strategy for Peregrine Falcon focused on southern population (sink)

Metapopulation: A population of a species that consists of several subpopulations linked together by immigration and emigration.

Metapopulation, linked by local subpopulations Patch Size Spatial structure Linkage

Metapopulation: Note: Fragmented populations that is not linked are not considered to be a metapopulation. Rescue Effect: local extinction of a subpopulation can be prevented by occasional immigrants that arrive from neighboring patches

A fundamental assumption of the original metapopulation concept 1) Space is discrete 2) It is useful and possible to distinguish between habitat patches that are suitable for the focal species and the rest of the environment, often called matrix Three critical elements: 1) Density dependence in local population dynamics 2) Spatial asynchrony in local population dynamics (independent of other subpoulations) 3) Limited dispersal linking the local populations (migration has no real effect on local dynamics in the existing populations)

Sources and Sinks in a Metapopulation

Population Viability depends on: 1. Demographic uncertainty (stochasticity) 2. Environmental uncertainty (stochasticity) 3. Natural catastrophes 4. Genetic uncertainty (stochasticity)

Population Viability Analysis (PVA) PVA is the study of how these four factors interact to determine extinction probability of a population to estimate MVP. The MVP is the product MVP - Minimum Viable Population-imply some thresholds for the # of individuals that will insure (at some acceptable level of risk) that a population will persist in a viable state for a given interval of time Population persistence analysis

Population Viability depends on: 1. Demographic uncertainty (stochasticity) BIDE + age structure + sex ratio Metapopulation structure Fragmentation the immediate precursor for extinction independent of individuals

Population persistence in years Immigration rate (individuals/year)

% Extinction

Population Viability depends on: 2. Environmental uncertainty (stochasticity) A decrease in habitat quantity Habitat disturbance or deterioration in quality Realized via demographic stochasticity A species also depends on habitats: Types --- where a species is (distribution) Quality (suitability) --- population features: density (abundance), fecundity, body size Quantity (areas) --- survival of a species (big mammals) Pattern (arrangement) --- habitat distribution for a metapopulation

Population Viability depends on: 3. Natural catastrophes Sudden change in environments Infrequent In fact, they are large environmental changes Fires Storms Hurricanes Earthquakes Volcanoes

4. Genetic uncertainty (Stochasticity) Mutation: an alteration of an allele (or alleles) into a new allele (new alleles) due to changes in molecules, gene sequences or chromosomes Bottle neck: a sudden reduction in a population size causes a genetic drift Genetic drift: random changes in allele frequency due to chance alone, often occurring in a small population (so-called sampling error) Founder effect: a genetic drift occurs when a few individuals separate from a large population and establish a new one Gene flow: the change in allele frequencies due to immigration or emigration

PVA Model Biology of Individuals Environmental Factors Population Dynamics (demography) Population Survival or Extinction

PVA Model Environmental disturbance Biology of Individuals Environmental Factors --Growth --Population (P) --Distribution Population Dynamics (demography) Genetic effective P size Demographic uncertainty Extinction (Deterministic) Extinction

Deterministic extinction: extinction resulted from some inexorable change or force from which there is no hope of escape. E.g. -- Deforestation -- Glaciations -- Removal a food source from animals

PVA Model Major loss of habitat Biology of Individuals Environmental Factors Population Dynamics (demography) Extinction (Deterministic) Fragmentation -- Population size -- Distribution Extinction Demographic randomness

The case study of a bird: the Florida Scrub Jay 1. Metapopulation types 2. Biology of the bird 3. Spatial distribution of the bird 4. Metapopulation structure Dispersal distance Patch occupancy Population viability analysis Characterization of metapopulation 5. Conservation rules

Biology of the Bird, the Florida Scrub Jay Florida’s only endemic bird species Habitat specialist-scrub community on sandy infertile soils Strong preference for low, open habitats with numerous bare openings and few or no pine trees, which are caused by frequent fires Food: acorns in winter Territorial defenders 10 ha per family Juveniles dispersal after one year The bird was listed as threatened species in 1987 by the U.S. Fish and Wildlife Service (USFWS)

Distribution of Florida scrub jay groups in 1993 Distribution of Florida scrub jay groups in 1993. Note the discontinuous distribution and variability in patterns of aggregation

Dispersal Distance (km) A subpopulation buffer is the distance where occupancy rates remain high; Accumulative 97% Frequency 85% 3.5 km 6.7 km Dispersal Distance (km) From natal to breeding territories 1970-1993

The metapopulation buffer is the smallest interpatch distance where occupancy rates reach their minimum Proportion of occupied patches Interpatch Distance (km)

Distance between patches (km) Occupancy Proportions Pairs Distance between patches (km) Occupancy Proportions 1-2 1-3 1-4 1-7 1-8 1 1.9 1.5 4 13 2/5 7 8 1

Statewide jay distribution with dispersal buffers Statewide jay distribution with dispersal buffers. Shaded areas depict subpopulations within easy dispersal distance (3.5 km) of one another (191 separate subpopulations. Thick outer lines delineate demographically independent (42) metapopulations separated from each other by at least 12 km A metapopulation 12 km 3.5 km A subpopulation

Only Six subpopulations > 100 birds Total 191 subpopulations Frequency Only Six subpopulations > 100 birds Subpopulation Size (# of birds) Numbers above the bars indicate the number of jay pairs

Frequency Metapopulation Size Nonequilibrium metapopulations Total 42 metapopulations Frequency Metapopulation Size Numbers above the bars indicate the number of jay pairs.

Metapopulation Types A. Patchy B. Classical C. Nonequilibrium A dispersal buffer-an isoline of equal dispersal probability A subpopulation A. Patchy B. Classical C. Nonequilibrium D. Mainland-Island

Nonequilibrium metapopulation Functional subpopulation based on frequency of dispersal beyond them Separate metapopulations based on poorly likelihood of dispersal among them A set of small patches in which each has a high probability of extinction and among which little or no migration occurs. Local extinction are not offset by recolonization, resulting in overall decline toward regional extinction.

Classical metapopulation A set of small patches that are individually prone to extinction but large enough and close enough other patches that recolonization balances extinction.

Patchy metapopulation Patches so close together that migration among them is frequent; hence the patches function over the long run as a continuous demographic unit.

Mainland-island metapopulation A mixture of large and small patches close enough to allow frequent dispersal from an extinction-resistant mainland to the extinction-prone islands

Patch Size Highly connected Patchy Mainland- Mainland Patch isolation Island Classical High isolated Nonequilibrium Disjunct All small All large Patch Size Fig. 9.3.

Mn-Mainland Md-midlands I-islands Total of 4 island subpopulations with 2 pairs in 1 subpopulation Total of 8 island populations with 1 subpopulations of one pair

Examples of Nonequilibrium metapopulations Fig. 9.10 North Gulf Coast of Florida: each of the 6 metapopulations contains fewer than 10 pairs of jays, except for the centrally located system that contains a single, midland-sized subpopulation

Fig 9.11. Examples of a “classical” metapopulation from 3 counties in central Florida. Note the occurrence of jays in small islands of intermediate distance from one another.

Fig 9.12. Portion of the largest mainland-midland-island metapopulation in interior Florida.. The large central subpopulation (enclosed by the thin black line) contains nearly 800 pairs of jays. Small subpopulations to the south and east are within known dispersal distance of the large, central mainland. A small metapopulation to the west (in DeSoto County) contains a single subpopulation of 21 territories.

Conservation Rules for the Florida scrub jay Preserve the cores Preserve all potentially viable metapopulations Preserve or enhance existing persistence probabilities Prohibit the splitting of a metapopulation Maintain connectivity within a metapopulation

A comparison between island biogeography and metapopulation Equilibrium: Species richness vs Population Community approach vs population approach: Community conservation (species richness-area relationship) vs focal species conservation Island theory ignore the changes in the presence and absences of individual species Among-patch movement

Shift to Metapopulation paradigm in conservation: Metapopulation concept and approach is taking over the equilibrium theory of island biogeography in conservation biology Shift in the conception of nature as an equilibrium world to non-equilibrium one Population genetics – genetic drift and inbreeding in a small population, becomes important because conservation question like “what is minimum viable population?” needs to be addressed. Species protection: the role of demographic and environmental stochasticity Metapopulation concept incorporate spatial structure into population dynamics – most significant, linked to habitat fragmentation Metapopulation models rescued small sites from their devaluation by island biogeography theory.

Landscape Approach: Landscape: A mosaic of habitat patches across which organisms move, settle, reproduce and eventually die. Heterogeneous within a landscape Patchy distribution of individuals - patches

Landscape Approach Modeling - spatially explicit models Incorporate: heterogeneous habitats patchy distribution of organisms Depict: The landscape structure The population demography Project: the outcome when a disturbance to habitats occurs, thus provide a management tool

Spatially explicit model A metapopulation model incorporate the actual locations of organisms and suitable patches of habitat, and explicitly consider the movement of organisms among such patches. Case of the Northern spotted owl

Case of Northern Spotted Owl Habitat: mature, old-growth coniferous forests Old, dense, large-trunk forest stands: foraging, cover, nesting, breeding, fledging of young Life history: juvenile dispersal from their natal areas, in search for both a suitable site and a mate Timber harvest, fire, clearing for agriculture and urban development reduce the habitat to 10% of original Sparked the struggle between stakeholders Very intense, prolonged battle A petition for federal intervention under Endangered Species Act, -- given threatened status in 1990

Landscape simulation suitable habitat, randomly scattered Fig. 8 The results are based on 30 simulations.

Landscape simulation Suitable habitats, 3 small blocks Fig. 9. The results are based on 30 simulations.

Landscape simulation Suitable habitats, a large block Fig. 10 The results are based on 30 simulations.

Landscape simulation Suitable habitat, 1 large irregular block Fig. 11. The results are based on 30 simulations.

Landscape simulation Suitable habitats, irregular blocks like riparian corridors Fig. 12. The results are based on 30 simulations.

Suitable habitats, clusters with marginal habitat Landscape simulation Suitable habitats, clusters with marginal habitat Standard deviations Fig. 13 The results are based on 30 simulations.

Probability of Extinction Endangered Species -- in danger of extinction throughout all or a significant portion of its range Threatened species -- likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. Critical Species -- facing a very high probability of extinction and require special conservation measures. 200 Safe 150 Vulnerable Endangered Years 100 50 50 20 10 Critical 0.2 0.4 0.6 0.8 1.0 Probability of Extinction