Landscape Ecology Notes

Landscape Ecology

Introduction

• Landscape ecology is the study of the composition, structure, and function of landscapes.
• It focuses on:
  • Spatial heterogeneity.
  • Broader spatial extents than traditionally studied in ecology.
  • The role of humans in creating and affecting landscape patterns and processes.

Landscapes

• A landscape is an area of land containing a heterogeneous mosaic of habitat patches that interact.

Mosaic

• A mosaic is a patchwork of different types of land cover.
• It is a function of:
  • Climate, geology (drainage, erosion, deposition).
  • Biotic processes.
  • Abiotic factors.
  • Species interactions.
  • Disturbance.

Disturbance

• Disturbance is a discrete event in time and space that alters the structure of populations, communities, and ecosystems, causing changes in resource availability or the physical environment.
  • Abiotic (e.g., fire, drought, flood, volcano).
  • Biotic (e.g., grazing, beaver activity).
  • Human initiated (e.g., croplands/pastures, timber harvesting).

Landscape characteristics

• Landscape composition: What land cover and vegetation types are present within the landscape, and the area occupied by each of them.
• Landscape configuration: How land cover and vegetation types are spatially arranged and distributed throughout the landscape.
  • Fragmentation
  • Shape irregularity
  • Connectivity
  • Edges

Disturbances and Succession

• Disturbances alter the landscape, giving way to succession.
• Shifting mosaic: The collection of patches, each in a phase of succession.

Shifting-Mosaic Steady State

• Shifting-mosaic steady state: Each patch is continuously changing, but the average across the landscape stays relatively the same.

Connectivity

• Connectivity: Proximity of patches to each other influences the ability for interactions among patches to occur.
  • Landscape connectivity: The degree to which a landscape facilitates or impedes the movement of organisms.
    • Among habitat patches.
    • Or across the habitat existing in that landscape patch.

Importance of Connectivity

• Connectivity is a major factor when considering the conservation of biodiversity and ecosystem function.
• Conserving and improving connectivity is a major part of land management worldwide.

Patches, Matrix, Boundaries, and Corridors

• Patches: Areas of more or less homogenous cover in relation to the surrounding environment.
• Matrix: Communities that surround each patch.
• Boundaries: The place where the edge of one patch meets the edge of another adjacent patch or surrounding matrix.
• Corridors: Routes that facilitate movement between patches.

Landscape Scale

• A landscape is not defined by size, but by scale relative to the organism or process of interest.
  • Could be a few square meters or a few square kilometers depending on the process or organism studied.

Boundaries

• Boundaries are transition zones between patches and can be:

  • Abrupt, usually a permanent part of the landscape (e.g., pond edge, forest edge).
  • Result of disturbance (e.g., wildfire, timber harvesting) and subject to successional changes over time.

• Boundaries:

  • Vary in length; can be straight, convoluted, or perforated.
  • Dynamic.

Transition Zones

• Also have vertical structure or height.

Ecotones

• Ecotone: transitional zone with wide borders between adjoining patches.

Boundary Characteristics

• Boundaries are blends of adjacent patches and offer unique habitats.
• Influenced by boundary area and contrast between two areas.
• Often populated by a rich diversity of organisms (edge effect).
• Greater contrast = greater diversity.
• Edge species are those that are restricted exclusively to edge environments.

Boundary Effects

• Boundaries also attract predators, which use edges for travel/hunting.
• Can facilitate/restrict dispersal.

Patch Size and Species Diversity

• Larger patches have:
  • Higher species diversity.
  • More individuals of each species.
• Body size related to:
  • Home range size; larger animals need larger home ranges.

Edge vs. Interior

• The ratio of edge:interior decreases as habitat size increases.
• Interior species: Require environmental conditions characteristic of interior habitats and stay away from the abrupt changes associated with boundaries.

Bird Species Distribution

• Some birds are edge species, interior species, or area-insensitive species.
• Study shows optimal woodland size is 24 ha. for maximum bird diversity.

Landscape Connectivity - Structural vs. Functional

• Landscape connectivity: The degree to which the landscape facilitates or impedes the movement of organisms among patches.
  • Structural connectivity: Physical arrangement of habitat patches on the landscape.
  • Functional connectivity: The degree to which the landscape facilitates the movement of organisms and is a function of both the physical structure of the landscape as well as the behavioral responses to the structure.

Corridors

• Corridors:
  • Function as travel lanes and interconnect to form networks.
  • Help facilitate species movement.
  • Offer dispersal routes for some organisms.
  • Filter effect: allows some organisms passage but restricts others.
    • Ex. Some butterflies are affected by hedgerows.
    • Butterflies needed gaps > 1 m to disperse.

Negative Effects of Corridors

• Corridors can have negative effects on some organisms:
  • Predators use them for hunting.
  • Can be areas of higher disease and increased spread.
  • Can increase invasive species.

Wildlife Corridors and Conservation

• Tracts of land or habitat that are linked and allow wildlife to travel from one location to another to find food, shelter, a mate, and a place to raise their young.
• Ensure genetic exchange between wildlife populations.
• Urbanization, highways, and agriculture are just some of the challenges that keep wildlife from dispersing and make them vulnerable to predators and many other dangers.
• Help wildlife travel to the places where they can find what they need.

Threats to Wildlife Populations

• Largest threat to wildlife populations in U.S. (NWF 2014).
• One of four greatest threats to effective management of National Lands (USDA Forest Service 2014).
• Key driver of species loss and a global biodiversity crisis (e.g., Sax and Gaines 2003).
• Linked with habitat degradation (e.g., invasive species and altered disturbance regimes (Didham et al. 2007)).

Ocelot

• The U.S. ocelot population teeters on the brink of extinction. Today, these cats are found only in
  the southernmost part of Texas. Biologists estimate that fewer than 50 remain in the wild.

Ocelot Mortalities

• Ocelot Mortalities Reported from June 2, 2015 to April 22, 2016

Ocelot Facts:

• Ocelots are federally listed as endangered in the United States.
• \< 80 Ocelots remain in the country
• Unlike most other cats, ocelots can turn their ankle joints around, allowing them to climb down a tree headfirst.
• Ocelots once ranged from South Texas up
  into Arizona, Arkansas, and Louisiana
• They are now found only in
  South Texas ranchlands and the Laguna
  Atascosa National Wildlife Refuge.
• Top predators in the thorny brush forests of Texas
• Ocelots mostly prey onrabbits, mice, rats and birds.
• In Texas, ocelots relyon thorny brush for shelter and protectionand require a lot of space: male needs 25 square milesof territory.
• 95\% OF THE OCELOT'S THORNYBRUSH HABITAT HAS BEEN LOST.
• 40% of the ocelots studied over the past 30 years have been killed by vehicles.

Saving the Endangered Ocelot

• THE U.S. FISH AND WILDLIFE SERVICE AND PARTNERS WORK TO PROTECT OCELOTS IN SOUTH TEXAS BY:
  • Monitoring ocelots living on the refuge and private lands
  • Protecting, restoring and connecting thorn forest habitat.
  • Working with the Texas Department of Transportation to install under road
    wildlife crossings that help keep ocelots off the road.
  • Planning to translocate (move ocelots within Texas and from Mexico to bring much needed genetic diversity to the small remaining population.