noc21-bt21-lec10

Threats to Wildlife: Push and Pull Factors

Introduction to the Module

• The module focuses on "Threats to Wildlife" and consists of three lectures covering push and pull factors, species threats through ecotoxicology, and developmental hazards.

Biogeography: Understanding Species Distribution

• Different organisms inhabit specific regions; for example, polar bears are found in Arctic areas while elephants reside in Tamil Nadu. This raises questions about the factors influencing their distribution.

• The field of biogeography studies the geographical distribution of life on Earth, exploring not only where organisms are located but also why they are found in those locations.

• Biogeography seeks to explain patterns observed across continents, islands, and oceans regarding species' presence or absence in certain areas. For instance, it examines why polar bears do not exist in India or why elephants are absent from Siberia.

Range of Species

• The range or distribution of a species refers to the geographical area where it can be found; for example, Uttarakhand is within the range of elephants while Siberia is not.

• Understanding a species' range helps clarify its habitat preferences and ecological requirements. This concept is crucial for conservation efforts aimed at protecting wildlife populations.

Major Habitats Overview

Alpine Meadows

• Alpine meadows are cold grasslands located in mountainous areas like Jammu & Kashmir and Himachal Pradesh; they support various species dependent on grasses such as tahr and smaller mammals like rats and rabbits.

Alpine Forest

• Found at lower elevations than alpine meadows, alpine forests typically consist of coniferous trees adapted to cold climates with small leaves that prevent snow accumulation on branches. These adaptations help trees survive harsh weather conditions.

Deciduous Forest Types

• Moist Deciduous Forest: Characterized by high moisture levels with dominant Sal trees; these forests shed leaves seasonally to conserve water during dry periods or protect against extreme cold during winter months. An image from Uttarakhand illustrates this habitat well.

• Dry Deciduous Forest: Dominated by teak trees; these forests exhibit significant leaf shedding during dry seasons as seen in an image from Madhya Pradesh where the forest floor is covered with fallen leaves due to seasonal changes.

Scrub Forest

• Scrub forests thrive in regions with limited water availability characterized by warm climates and low rainfall; these habitats support unique flora adapted to arid conditions but face challenges due to environmental stressors such as drought.

Habitat Diversity in Arid Regions

Open Forests and Vegetation Types

• In areas with less rainfall, large trees cannot thrive, leading to the formation of open forests characterized by a sparse canopy.

• The vegetation typically includes short plants such as grasses, shrubs, and smaller trees that adapt to dry conditions.

Sand Dunes and Endemic Species

• Sand dunes are found in extremely dry locations, exemplified by Jodhpur's clear skies and minimal cloud cover.

• Despite limited vegetation, these regions host endemic species like the spiny tail lizard, which is adapted to intense sunlight and scarce water.

Estuaries: A Biodiversity Hotspot

• Estuaries occur where rivers meet the sea, creating a gradient of salinity from freshwater to brackish water.

• This salinity gradient supports diverse species that can thrive in varying saline conditions.

Rann of Kutch: Unique Ecosystem Dynamics

• The Rann region experiences seasonal flooding during rains but becomes parched in other seasons; it features flat terrains with some grasses.

• Endemic species like the Indian wild ass inhabit this area alongside organisms such as flamingos that thrive in brackish waters.

Lagoons: Chilika Lake Example

• Lagoons like Chilika Lake allow seawater to mix with freshwater from rivers, creating unique habitats with varying salinity levels.

• Shallow depths (less than 60 meters) promote high productivity due to sunlight penetration throughout the water column.

Flood Plains: Seasonal Growth Patterns

• Flood plains near rivers flood during rainy seasons; post-flooding leads to vacant wet grounds ideal for grass growth.

• These areas support large herbivorous populations including endemic species like rhinoceroses.

Shola Forest Ecosystems

• Shola forests found in Tamil Nadu and Karnataka exhibit a balance between grasses and trees without one type invading the other.

• This dynamic equilibrium allows animals to graze safely while having access to forest cover for protection against predators.

Equatorial Forest Characteristics

Equatorial Forests and Biodiversity

Characteristics of Equatorial Forests

• Equatorial forests exhibit profuse vegetation growth, leading to complete canopy closure where tree canopies touch each other.

• The trees in these forests are notably tall, with height comparisons made to elephants for scale.

• These forests support a vast amount of biodiversity due to abundant food production.

Mangroves: A Unique Habitat

• Mangroves are found at the intersection of land and sea, featuring trees adapted to both environments.

• They possess specialized adaptations like pneumatophores (exposed roots for aeration) and vivipary (fruits germinate while still on the tree).

• Mangrove roots provide shelter for various fish species, contributing significantly to biodiversity.

Distribution of Species

Snow Leopard Habitat

• The snow leopard is primarily found in mountainous regions, as illustrated by its distribution map showing specific habitats.

• Adaptations such as camouflage and a thick fur coat enable snow leopards to thrive in snowy environments.

Coral Reefs: Environmental Requirements

• Coral reefs are located in oceans with moderate temperatures and clear waters; they do not thrive in muddy conditions.

• Climate plays a crucial role in determining the locations where organisms like coral reefs can be found.

Impact of Climate on Species Distribution

Altitudinal Zonation

• Moving from the equator towards the poles reveals distinct forest types: tropical forests transition into subtropical and temperate forests based on altitude.

• At higher altitudes near the equator, subtropical forests appear despite being geographically close to tropical regions.

Commonalities Across Regions

Understanding Vegetation Distribution: Push and Pull Factors

The Role of Climatic Conditions in Vegetation

• Similar climatic conditions lead to similar vegetation types across different latitudes, prompting the question of why certain species thrive in specific areas.

• The concept of pull factors is introduced, which are conditions that attract organisms to an area, such as abundant food and a suitable climate.

• Conversely, push factors drive organisms away from areas due to unfavorable conditions like food scarcity or inhospitable climates.

Case Study: Polar Bears and Their Habitat

• Polar bears find pull factors in the Arctic due to sufficient food availability and lack of predators; however, regions like Madhya Pradesh present push factors with high temperatures unsuitable for them.

Analyzing Vegetation Patterns in Shivalik Hills

• Observations reveal stark differences in vegetation on steep slopes versus less steep areas, raising questions about the underlying reasons for these patterns.

• Steep slopes often lack soil due to erosion during rains, acting as a push factor preventing plant growth. Additionally, south-facing slopes experience higher evaporation rates leading to moisture scarcity.

Soil and Moisture: Key Determinants for Plant Growth

• Areas with gentler slopes retain soil better and have more moisture available, serving as pull factors that support plant life.

Liebig's Law of the Minimum Explained

• Liebig's law states that biological processes are limited by the least available factor relative to requirements; this principle applies directly to plant growth.

• Essential nutrients like nitrogen (N), phosphorus (P), and potassium (K) are critical for plants; if one nutrient is deficient compared to others, it becomes the limiting factor for growth.

Implications of Nutrient Availability on Plant Growth

• In a scenario where nitrogen is 80% available but phosphorus only 50%, phosphorus limits plant growth according to Liebig's law.

Understanding Environmental Factors and Species Distribution

The Role of Phosphorus and Shelford's Law

• The lack of phosphorus acts as a push factor for species distribution, influencing their geographical presence.

• Shelford's law of tolerance states that the distribution of a species is controlled by the environmental factor with the narrowest range of tolerance. This concept highlights how specific conditions dictate where organisms can thrive.

Changing Environmental Conditions

• Recent observations indicate that changing environmental conditions allow organisms to extend their range, even if their tolerance remains unchanged. This adaptability is crucial in understanding species migration patterns.

• Global warming serves as a prime example, affecting insect distributions based on temperature tolerances, particularly in mosquitoes which are limited by low temperatures at higher altitudes.

Impact of Global Warming on Species Range

• As global temperatures rise, previously inhospitable areas become suitable for certain species like mosquitoes, leading to an increase in their altitude range and potential spread of diseases such as malaria.

Allelopathy: A Push Factor in Ecosystems

• Allelopathy refers to the phenomenon where certain organisms release chemicals that inhibit or kill other organisms, exemplified by antibiotics like penicillin produced by Penicillium fungi. This interaction showcases competitive dynamics within ecosystems.

• In dry deciduous forests dominated by teak trees, fallen leaves secrete chemicals that inhibit ground cover vegetation growth, demonstrating allelopathic effects beyond microorganisms to larger plant communities.

Experimental Demonstration of Allelopathy

• An experiment illustrates how grass inhibits apple tree seedling growth through allelopathic secretions; water runoff from grass-soil mixtures shows reduced growth compared to control groups without grass influence. This method effectively isolates the chemical impact on plant development.

Predation and Its Impact on Species Distribution

Understanding Predation

• Predation is defined as the phenomenon where one species hunts or consumes another for food, influencing population dynamics.

• A classic example involves sea urchins regulating algae distribution; high sea urchin populations lead to low algae presence.

• An experiment demonstrated that removing sea urchins allowed algae to thrive within a year, confirming their role as predators affecting prey abundance.

Prey-Predator Dynamics

• The relationship between predator and prey can be reciprocal; prey availability can influence predator distribution.

• For instance, tigers are found in areas with deer (prey), while Drosophila pachea relies on a specific cactus for survival, showcasing how prey can dictate predator locations.

Competition and Its Role in Species Distribution

Interspecific Competition

• Interspecific competition occurs when two species compete for resources like food or space, impacting their distributions.

• An example includes red-winged blackbirds displacing redwings from central territories due to competitive aggression observed in March 1959.

Effects of Competition

• The displacement of redwings illustrates how one species can act as a push factor against another, altering habitat occupancy without environmental unsuitability.

Behavioral Factors Influencing Habitat Selection

Habitat Selection Explained

• Habitat selection refers to behavioral responses leading organisms to prefer certain habitats over equally suitable alternatives.

Case Study: Chipping Sparrows

• Research on chipping sparrows shows they exhibit preferences for pine trees over oak trees despite both being viable habitats.

Habitat Selection and Dispersal Mechanisms

Habitat Preference in Chipping Sparrows

• Chipping sparrow chicks show a strong initial preference for pine foliage, spending 67% of their time there compared to only 33% in oak.

• When raised in an environment with oak leaves, these chicks gradually develop a preference for oak, eventually spending 54% of their time on it after release into the forest.

• This shift indicates that habitat selection has both innate and learned components; birds can adapt their preferences based on environmental exposure.

Understanding Dispersal

• Dispersal is defined as the movement of individuals away from their birthplace to new habitats for survival and reproduction, crucial for species distribution.

• Various mechanisms facilitate dispersal, such as wind or water aiding seed movement, and animals consuming fruits that carry seeds to new locations.

Types of Dispersal

Diffusion

• Diffusion involves gradual movement over generations across hospitable terrain; an example includes lions moving through the Gir landscape.

Jump Dispersal

• Jump dispersal refers to rapid movement over large distances often across unsuitable terrain. An example is rats hitching rides on ships between islands.

• Zebra mussels also exemplify jump dispersal by traveling via ballast water in ships, allowing them to cross inhospitable environments quickly.

Secular Dispersal

• Secular dispersal occurs slowly enough that populations diverge significantly from their original groups; this is seen in human migration out of Africa.

Factors Influencing Species Distribution

• The presence or absence of species in certain locations depends on successful dispersal. For instance, if rats disperse from one island to another where conditions are suitable (space and food), they will establish a population there.

Anthropogenic Effects on Habitats

Understanding Organism Distribution Through Transplantation Experiments

The Role of Transplantation Experiments

• Transplantation experiments help elucidate why certain organisms are found in specific regions, revealing insights into their abundance and distribution.

• In these experiments, organisms are moved from a site where they thrive (green zone) to areas where they do not exist (yellow and red zones), allowing researchers to assess survival rates.

• If organisms survive in the new area (yellow zone), it indicates that dispersal limitations may be the reason for their absence; however, if they die in another area (red zone), it suggests environmental factors preventing their survival.

Factors Influencing Distribution

• The outcomes of transplantation experiments can indicate whether distribution is limited by physical barriers, habitat preferences, or biotic interactions such as predation and competition.

• Observations from these experiments can clarify if an organism's localization is due to dispersal issues or behavioral aspects related to habitat selection.

Analyzing Biotic and Abiotic Factors

• If accessibility is not an issue but there’s no preference for habitats, then biotic factors like predation or disease might limit distribution.

• Further experimentation can determine if other species regulate distribution through competitive interactions or parasitism.